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FEDERAL INSTITUTE OF EDUCATION, SCIENCE AND

SAO PAULO TECHNOLOGY
CUBATÃO CAMPUS

HIGHER COURSE IN AUTOMATION TECHNOLOGY

AND CONTROL OF INDUSTRIAL PROCESSES
CONTINUOUS

APOSTILLE OF

HIGHER COURSE IN TECHNOLOGY IN AUTOMATION AND

CONTROL OF CONTINUOUS INDUSTRIAL PROCESSES

ASSEMBLY:
PROFESSOR MARCELO S. COELHO

Revision 2 – JANUARY/2009
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SUMMARY
STANDARD: MODBUS ...................................................................................................................................... 1
MODBUS STANDARD ...................................................................................................................................... 11
EXERCISE ON MODBUS ..................................................................................................................... 12
STANDARD: HART .............................................................................................................................................. 13
TOPOLOGY ................................................................................................................................................... 14
COMMUNICATION MODES ....................................................................................................................... 16
CABLES ........................................................................................................................................................ 17 HART
COMMANDS ..................................................................................................................................... 18 DEVICE
DESCRIPTION LANGUAGE .......................................................................................................... 18
MULTIPLEXERS.................................................................................................................................. 18 EXERCISES
ON HART ..................................................................................................................... 21
DEFAULT: DEVICENET ................................................................................................................................................ 22
DEVICENET PHYSICAL LAYER AND TRANSMISSION MEDIUM ..............................................................................
23 GROUNDING ........................................................................................................................................ 31
ADDRESSING THE INSTRUMENT IN THE DEVICENET NETWORK: ........................................................... 33
INDICATORS OF DEVICENET DEVICES ..................................................................................... 34 DEVICENET
PROJECT DETAILS ........................................................................................ 35 SIZING THE VOLTAGE DROP
ALONG THE NETWORK .......................................................... 40 EXERCISE ON
DEVICENET ............................................................................................................... 44 DATA EXCHANGE METHODS
IN COMMUNICATION.................................................................................. 45
STANDARD: FIELDBUS FOUNDATION .......................................................................................................... 48
BASIC STRUCTURE ................................................................................................................................... 51
DETAILING PROJECTS WITH FIELDBUS ............................................................................................ 69 SOFTWARE
LEVEL .............................................................................................................................. 74
STANDARD: PROFIBUS ................................................................................................................................... 82
THE PROFIBUS FAMILY .............................................................................................................................. 82 BASIC
FEATURES ................................................................................................................... 85 TRANSMISSION
TECHNOLOGY ............................................................................................................ 88 PROFIBUS BUS ACCESS
PROTOCOL ................................................................................. 95 PROFIBUS-
PA ......................................................................................................................................... 106
STANDARD: AS-I .............................................................................................................................................. 121
AS-I NETWORK COMPONENTS.............................................................................................................. 124
TECHNICAL CHARACTERISTICS .............................................................................................................. 127
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STANDARD: MODBUS

The Modbus network is a relatively simple network, developed with the aim of
allowing the interconnection of control devices, such as programmable controllers
and computers, normally of the PC type.

Modicon, now Schneider Electric, introduced the Modbus protocol to the market in
1979. Schneider helped develop an independent user and developer organization
called Modbus–IDA, a non-profit organization of users and vendors of automation
devices to promote the adoption of the Modbus protocol suite and the evolution of
the addressing architecture for distributed automation systems in various
market segments. Modbus–IDA provides the infrastructure for obtaining and
sharing information about the protocols, their applications, and device certification
to simplify user implementation.

The Modbus network is intended for communication between control equipment.

The respective protocol defines a set of messages that allow reading and writing to
remote variables (bits/words of internal memory, input and output lines).

Figure 1.

MODBUS STANDARD is used for communication between PLCs and control devices.
data input and output, intelligent electronic instruments (IEDs) such as protection
relays, process controllers, valve actuators, energy transducers, etc. The physical
medium is RS-232 or RS-485 in conjunction with the master-slave protocol.
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MODBUS PLUS is used for communication between programmable logic controllers, I/O
modules, electronic motor starters, human-machine interfaces, etc. The physical medium is RS-485
with transmission rates of 1 Mbps, medium access control by HDLC (High Level Data Link Control).

MODBUS TCP/IP is used for communication between supervisory systems and programmable
logic controllers. The Modbus protocol is encapsulated in the TCP/IP protocol and transmitted over
standard Ethernet networks with CSMA/CD media access control.

When communicating on a Modbus network, the protocol determines how the

The device will know its address, how it will recognize a message addressed to it, how it will determine
what type of action to take, and how it will extract the data or other information contained in the
message. If a response is required, how the device will construct a message and send it.

The master can address messages to an individual slave or send messages to all slaves
(broadcast). Slaves return a message only for queries specifically addressed to them. Broadcast messages
do not generate responses.

More specifically, the Modbus protocol defines:

• the requests that control devices can send to other devices;

• how they respond to these requests;

• the way errors are handled.

The Modbus protocol is based on a master-slave communication model, where a single device, the
master, can initiate transactions called queries. The other devices on the network (slaves) respond by
supplying the data requested by the master or executing an action commanded by it. The master is
usually a supervisory system and the slaves are programmable logic controllers. The roles of
master and slave are fixed when serial communication is used, but in other types of networks, a device can
assume both roles, although not simultaneously.

Devices connected to a Modbus network exchange data using a technique such as

Master-Slave where:

• only one device (designated as master) can initiate transactions.

• the other devices (called slaves) respond by sending the requested information to the master
(in the case of a read request) or by executing the action requested by the master (in the case of a write
request).

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Figure 2.

Messages sent by the master include the following fields:

•address of the slave to which the message is intended;

•code of the action to be performed (read/write, bit/word, ....);

•any data (in the case of write operations);

•code for error control.

Responses from slaves contain the following fields:

•confirmation of the action taken;

•any data (in the case of reading operations);

•code for error control.

In the query message, the function code informs the slave device with the respective
address which action is to be performed. The data bytes contain information for the slave,
for example, which register is the starting register and the number of registers to be read.
The error checking field allows the slave to validate the received data.

In the response message, the function code is repeated back to the master. The
Data bytes contain the data collected by the slave or its status. If an error occurs, the
function code is modified to indicate that the response is an error response and the data
byte contains a code that describes the error. Error checking allows the master to validate
the data received.

Figure 3.
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Note that all traffic is managed by the master. In fact, slaves can only
transmit a message after they have received a request from the master.

TRANSMISSION MODES

There are two transmission modes: ASCII (American Code for Information)
Interchange) and RTU (Remote Terminal Unit), which are selected when
configuring communication parameters.

ASCII

Each message byte is sent as two ASCII characters. During

transmission, gaps of up to one second between characters are allowed without
truncating the message. Some implementations use such silent intervals as
end-of-message delimiters, replacing the cr+lf sequence.

10 bits per byte: 1 start bit

7 bits of LSb data sent first

1 parity bit (even/odd) + 1 stop bit

0 parity bits + 2 stop bits

Error Checking Field: LRC Longitudinal Redundancy Check

Start : Address Function Data LRC END
(0x3A) 2 Chars 2 Chars N Chars 2 Chars CRLF

ASCII mode allows time gaps of up to one second between characters without
causing errors, but its typical message is twice as long as the equivalent message
using RTU mode.

RTU

Each message byte is sent as a data byte. The message must be

transmitted continuously, since pauses longer than 1.5 characters cause it to be truncated.

11 bits per byte: 1 start bit

8 bits of LSb data sent first

1 parity bit (even/odd) + 1 stop bit

0 parity bits + 2 stop bits

Error Checking Field: CRC

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Start Address Function Data CRC END

Silence 8 bits 8 bits N x 8 bits 16 bits Silence
3.5 chars 3.5 chars

RTU mode transmits information with a smaller number of bits, but the
message must have all its characters sent in a continuous sequence.

RTU mode is also called ModBus-B or Modbus Binary and is the mode
preferential.

Figure 4.

MESSAGE FORMAT

•Modbus/RTU messages have the following format:

Figure 5.
•Each message begins with a period of silence on the line of at least the
3.5 character transmission time.

•If a new message is received with a shorter time interval, the device will
consider it to be a continuation of the previous message (which will result in a CRC
error).

Figure 6.

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ADDRESS FIELD

The address field contains 8 bits and its valid address range is from 0 to 247 (0x00
to 0xf7 hexadecimal). Valid addresses for slaves are 1 to 247 (address 0 corresponds to
the broadcast address recognized by all slaves).

The master addresses a given slave by placing its number in the address field of the
message. In turn, the slave, when responding, also places its own number in the address
field of the message it sends to the master.

FIELD FUNCTION

The function field contains 8 bits.

This field specifies the action to perform, for example:

•read a set of input lines;

•write a set of memory registers;

•load or check the running program.

Valid function codes are 1-255, but each model only supports a subset of the
Modbus functions.

Figure 7.

When the slave correctly executes a function, it returns a message to the master
containing, in the function field, the code of the function executed.

If an error has occurred, the slave returns, in the function field, a code of the
function with the most significant bit set to 1.

Example:

If the master sent a message with function code 03 and an error occurred, the
slave will return:

•1000 0011 (Hexadecimal 83) in the function field and an error code in the date field
indicating the type of error that occurred.
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Note: Subsequent error handling is the responsibility of the master program.

DATA FIELD

The data field contains additional information necessary to execute the functions. For
For example, if it is a function to read n bits of memory, the data field specifies the
address of the first bit and the number of bits to read from that address.

If the function is executed normally, the response data field will contain
the data requested by the master. If an error has occurred, this field will contain
the respective code (as mentioned above).

CRC FIELD

The CRC field contains an error control code. CRC codes can be generated using
various algorithms.

As we have seen, each Modbus message consists of a sequence of bytes. In the

case of transmission via a serial line, each of these bytes is transmitted as a sequence
of bits.

The sequence of bits corresponding to a byte, as specified or not,

parity control, are as follows.

Error checking is optionally performed on the parity of each transmitted

byte and obligatorily by the LRC or CRC method on the entire message. LRC discards
the start and end characters of the message. CRC discards the start, parity and
stop bits of each byte.

The master device waits for a response for a specified amount of time
before aborting a transaction (timeout). The timeout should be long enough to
allow any slave to respond. If a transmission error occurs, the slave will not construct
a response to the master. A timeout will be detected and the master will take the
scheduled action.

Figure 8.

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MODBUS FUNCTIONS

Every device on a Modbus network must have its memory divided into
16-bit registers numbered according to the model presented.

The division is based on the memory structure of a PLC:

•Discrete outputs for ON-OFF actuators use one bit. Each register supports 16 outputs.

•Discrete inputs for ON-OFF sensors use one bit. Each register supports 16 inputs.

•Analog inputs use 16-bit registers for values obtained by A/D converters from analog sensor
signals.

•Memory Registers with 16 bits for values used internally in the PLC.

Figure 9.

The identification of the reading and writing commands (functions) are different according to
with the type of data to be read or written.

• Function 1 reads the status of the discrete outputs.

• Function 5 writes a single discrete output.

• Function 15 writes multiple discrete outputs.

• Function 2 reads the status of the discrete inputs.

• Function 4 reads the values of the analog inputs.

• Function 3 reads the values from the memory registers.

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• Function 6 writes a value to a memory register.

• Function 16 writes multiple values to memory registers.

READING VALUES FROM MEMORY REGISTERS – FUNCTION “3”

The following figure shows the structure of a message query corresponding to function
“3” for reading the values of memory registers.
ADDRESS FUNCTION HOME ADDRESS Number of Records (MSB) CRC
(MSB) (LSB) (LSB) (MSB) (LSB)
03
Figure 10.

The following figure shows the structure of a message response corresponding to

function “3” for reading the values of the memory registers.
ADDRESS FUNCTION Qty. BYTES DATA from 1st REGISTRATION. .... DATA from Last REGIST. CRC

(MSB) (LSB) .... (MSB) (LSB) (MSB) (LSB)

03

Figure 11.

In the illustration below we have an example where the master requests a reading of the
registers 40108 to 40110 of slave element 06.

In the memory registers area, the first register is “40001”, but this is
addressed as “0”. Therefore, if we need the information for address “40108”, we
should address it as “107”, which transformed into hexadecimal will be “6BH”.

Registers use 16 bits to encode information. These 16 bits are sent in two
separate bytes (HIGH BYTE and LOW BYTE).

Figure 12.

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ADDRESS FUNCTION HOME ADDRESS Number of Records (MSB) CRC

(MSB) (LSB) (LSB) (MSB) (LSB)
06 03 00 6B 00 03 XX XX

Figure 13.
In the response, the slave repeats the function code indicating a normal response.
amount of bytes specifies how many items are being returned.

The answers indicate:

• Record 40108: 02 2B(H) = 555

• Record 40109: 00 00(H) = 0

• Record 40110: 00 63(H) = 99

Figure 14.

ADDRESS FUNCTION Qty. BYTES DATA of 1st. Regist. DATA of 2nd. Regist. DATA of 3rd. Regist. CRC
(MSB) (LSB) (MSB) (LSB) (MSB) (LSB) (MSB) (LSB)
06 03 06 02 2B 00 00 00 63 XX XX

Figure 15.

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MODBUS TCP/IP

Launched in 1999, it was the first open protocol to use Ethernet and TCP-IP.

Since there is no difference between master and slave, any node with a TCP port can access any
other node, making it possible to implement point-to-point communication between former slaves.

The message is encapsulated in a TCP/IP packet. Commands are sent by a client using a TCP/IP
message to port 502 of a server, which responds with the desired data encapsulated in a TCP/IP packet.

TCP encapsulation did not modify the basic structure of the original message.
Modbus. The differences are in address interpretation and error checking.

Figure 16.

In addressing, the slave address field has been replaced by a single

byte called a Unique Identifier that can be used for communication via devices such as
gateways and bridges that use a single IP address to integrate multiple devices.

CRC or LRC fields are not used for error checking. The following fields are used:
mechanisms similar to those already existing in TCP/IP and Ethernet protocol.

By using TCP/IP packets, Modbus/TCP allows remote access via the corporate network backbone
and even the Internet, which can be both an advantage and a risk. LAN and Internet allow remote
operations, but require that safeguards be used to prevent unauthorized access.

Modbus/TCP has been criticized for using the “tedious” TCP protocol with its endless
confirmations to start a session and verify the integrity of the packets sent.

Critics also draw attention to the impossibility of prioritizing

messages, excess traffic due to the impossibility of broadcasts and indeterminism.

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EXERCISE ON MODBUS
Analyzing the figure, answer:

What is the maximum capacity of slave devices that can exist in a MODBUS network?

What is the physical medium access control technique used by the MODBUS standard?

Which fields make up the structure of a message (Frame) in the MODBUS standard.
Draw this structure.

Explain how a message is initiated in the MODBUS communication standard.

How many bits make up the “Address” field of the communication standard message?
MODBUS? Which range of addresses can be written with these bits?

Cite the code and its description of at least three functions in the MODBUS
communication standard.

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STANDARD: HART

The Hart protocol was introduced by Fisher Rosemount in 1980. Hart is a

acronym for “Highway Addressable Remote Transducer”. In 1990 the protocol was opened
to the community and a user group was founded.

The great advantage offered by this protocol is that it enables the use of
smart instruments over traditional 4-20 mA cables. Since the speed is low, the cables normally
used in instrumentation can be maintained. Devices capable of performing this hybrid communication
are called smart.

The Hart signal is modulated in FSK (Frequency Shift Key) and is superimposed on the signal
analog 4..20 mA. To transmit 1 a 1 mA peak-to-peak signal at a frequency of 1200 Hz is
used and to transmit 0 a frequency of 2200 Hz is used.

Communication is two-way.

Figure 17. Hart signal superimposed on 4..20 mA signal

This protocol allows, in addition to the PV value, other significant values to be

transmitted as parameters to the instrument, device configuration data, calibration and
diagnostic data.

The FSK signal is continuous in phase, imposing no interference on the signal.

analog. Standardization follows the Bell 202 Frequency Shift Keying standard.

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TOPOLOGY

The topology can be point-to-point or multi-drop. The protocol allows the use of up to
two masters. The primary master is a computer or PLC or multiplexer.

The secondary master is usually represented by hand-held configuration and calibration terminals.

There must be a resistance of at least 230 ohms between the power supply and the instrument for
the network to work. The handheld terminal must always be inserted between the resistor and the field
device as shown in the Figure.

Figure 18. Connecting an input to a HART instrument

The series resistor is usually already an integral part of single loop controller input cards and remote
input cards and therefore does not need to be added. Other measuring devices are inserted in series
in the current loop, which causes a voltage drop across each device.

For connecting output devices to an analog output, a shunt resistor is not required.

Figure 19. Connecting a HART output

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Figure 20. HART protocol with two masters

Figure 21. HART Configurator: HPC301 and HP311 HART Pocket Interface

Figure 22. Fluke 744 Multifunction Calibration Terminal and Fluke 707 Current Loop Calibrator
for HART Instruments

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MODES OF COMMUNICATION

The HART protocol can use several communication modes. The basic mode is the master-slave
mechanism. Each cycle of requesting and receiving a value lasts about 500 ms, which implies reading
two values per second.

Figure 23. HART communication in master-slave mode (default)

In the point-to-point topology, a second data transfer mechanism is possible. The instrument can
autonomously and periodically send the value of a variable, for example the PV. In the interval
between these transmissions, the master can execute a question and response cycle. The transmission
rate in this case increases to 3 or 4 per second. This mode is called burst or broadcast mode. The master
can send a message to interrupt this continuous sending of reply messages, at its convenience.

Each message can communicate the value of up to four variables. Each HART device can have
up to 256 variables.

Figure 24. HART communication in mode, supported by some devices

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When using a multidrop topology, the HART network supports up to 15 field instruments. Only
master-slave mode can be used. In this case the current value is kept at its minimum level of 4 mA and the
PV value must be read
through an explicit message.

Figure 25. HART network in multidrop topology

The major shortcoming of the multidrop topology is that the cycle time for reading each
device is about half a second and can reach one second. In this case for 15 devices the time will be 7.5
to 15 seconds, which is too slow for most applications.

CABLES

The maximum distance of the HART signal is about 3000 m with shielded twisted pair cable and 1500
m with single shielded multi-cable.

There are special intrinsic safety barriers that allow traffic from
HART signal.

Table 1.
Distance mm2
Cable type
maximum (AWG)
Twisted pair cable with
1534 m 0.2 (24)
single shield

Twisted pair cable with

0.5 (20)
3048 m shielding

The HART protocol uses the same cabling for field instrumentation
conventional.

The most limiting factor on cable length is its capacitance. The higher the
capacitance and the number of devices, the smaller the maximum allowable distance:

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Table 2. Maximum cable length as a function of cable capacitance

Instruments/
65 nF/km 95 nF/km nF/km nF/km
Capacitance 1
2800 2000 1300 1000
5 2500 1800 1100 900
10 2200 1600 1000 800
15 1800 1400 900 700

HART COMMANDS

Every HART device must accept a minimum repertoire of commands

called universal commands or common practice commands. For each device there will be specific
commands called device specific commands. Universal commands ensure interoperability between
field devices.

The Table shows examples of universal and specific commands:

Table 3. HART commands

Universal controls Device specific commands
Reading variables Model-specific functions
Lower and upper limit change Special calibration options
Zero and span adjustment Start, stop and reset totalizer
Start self test Select primary variable
Serial number Enable PID, change Set Point
Time constant values Adjust tuning parameters

All specific commands are optional, but if present they must be

implemented according to the specification.

DEVICE DESCRIPTION LANGUAGE

Every HART device is accompanied by a device description (DD) that describes all the
parameters and functions of the device. The ultimate goal is to gather all the characteristics so that a host
can fully communicate with the device, thus ensuring full interoperability between devices.

MULTIPLEXERS

Multiplexers are part of every new project involving HART networks.

Multiplexers function as a primary master that reads all process variables and status information
from all transmitters periodically, independently of the host. The host in turn reads the process variables
from the multiplexer. The host can also send commands and establish a conversation directly with a
field device. The multiplexer is essential when one of the project objectives is the control of instrumentation
assets (Instrumentation

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Asset Management). In older systems where this feature is to be implemented, multiplexers

can be placed in parallel with conventional connections to provide the continuous diagnostic
function of the instruments.

Figure 26. Emerson multiplexer used to fetch data for AMS asset management SW

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Figure 27. Unconventional use of the HART protocol

The figure above illustrates an unconventional use of the HART protocol. The
The instrument is programmed so that the 4..20 mA signal provides the value of the
manipulated variable, output of the PID algorithm of the block implemented by the instrument. This
signal is used to directly control the valve. The HART channel is used to perform loop supervision.

The Figure below emphasizes the series connection of the instrument and the actuator.

Figure 28. Interconnection between HART instrument and actuator

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HART EXERCISES
1) Search the Internet for data sheets for the following types of equipment:

Component Manufacturer Features

techniques
Pressure transmitter
Temperature transmitter
HART Scanner
HART Calibrator
Valve with HART interface

2) Mark True or False:

( ) The HART protocol transmits digital signals in the intervals between the
transmission of analog signals.

( ) Every instrument with HART transmitter supports burst mode transmission .

( ) Burst mode transmission provides better bandwidth utilization

of the transmission channel.

( ) It is possible to use burst mode in multidrop networks.

( ) When in multidrop topology, the PV value of each instrument cannot

be read from the current of 4..20 mA.

( ) A HART field device must respond to all universal commands.

() Instruments placed in parallel in a HART segment bring as

I benefit from shorter scan times.

( ) It is impossible for a HART instrument to have a PID module and act

directly onto an actuator in the field.

() HART instruments are not widely used in the world, this is their basis
installed is very small in 2003.

3) Compare the functionalities of the HART and Foundation Fieldbus networks.

4) Fifteen HART devices are connected in a multidrop line. Each

The device requires 12 Volts to operate and consumes 4 mA of current. 1 km of cable
with a resistance of 22 ohms per kilometer is being used in each conductor.
Calculate the minimum value of the source supply voltage and the power of the series
resistor (consider 250 ohms). What should be the maximum capacitance per meter of the cable?

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DEFAULT: DEVICENET

DeviceNet is a communications link for connecting industrial devices (such as limit

switches, photoelectric sensors, motor starters, process sensors, bar code readers, variable
frequency drives, user interfaces, among others) to a network.
, eliminating multiple cables.

Figure 29.

Direct connectivity provides improved communication between devices,

as well as important device-level diagnostics not easily accessible or available in conventional I/O
devices.

DEVICENET FEATURES AND FUNCTIONALITY

DeviceNet is an open network, and the specification and protocol can be obtained from the Open
DeviceNet Vendors Association, Inc. (ODVA). DeviceNet is based on a communications protocol called
CAN, which was originally developed by BOSCH for the European automotive market to
replace expensive cable harnesses with a low-cost network in automobiles. As a result, CAN
provides fast response and high reliability for applications such as ABS and air bag control.

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Table 4.
NETWORK SIZE Up to 64 knots
NET LENGTH Selectable according to speed
For 125 Kbps 500m
For 250 Kbps 250m
For 500 Kbps 100m 0
DATA PACKAGE to 8 Bytes
TOPOLOGY Linear (trunkline/dropline) with power and signal through the same cable

ADDRESSING Peer-to-peer with Multi-cast; Multi-master and Master/slave

FEATURES OF Removing and inserting devices from the working network
SYSTEM

DEVICENET PHYSICAL LAYER AND TRANSMISSION MEDIUM

The following figure shows the basic components of an installation with thick
cable and flat cable.

Figure 30.
Devices can be powered directly from the mains and communicate via
from the same cable, and can be removed or inserted without disconnecting the network.

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Table 5.

COMPONENT DESCRIPTION

Trunk (Trunk line) The main cable between the terminators, which can be thick, thin or
flat cable, connects the taps or the devices directly.
Derivation (Drop line) The derivation is made of thin or thick cable, connecting the devices to
the derivator (tap)
Node/Device An addressable device that contains a Devicenet chip
Termination Resistor 121ÿ resistor connected only at the end of the trunk
Power supply Used to power devices

Open-style connector Used with devices not exposed to harsh environments

Sealed-style connector Used with devices exposed to harsh environments

CABLES

The Devicenet network allows the use of thick and thin cables, in addition to flat cables. It is
also necessary to use termination and power supply on the network.

Figure 31. Thin and thick cable profile

Power taps can be added anywhere in the network, making redundant power possible. Trunkline
current is 8 amps (with thick cable) and 3 amps with thin cable. An opto-isolated design option
allows externally powered devices (e.g., AC starters and solenoid valves) to be used on the same
bus cable. Other CAN-based networks allow only a single power source for the entire network.

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THICK HANDLE

Figure 32.

THIN CABLE

Figure 33.

FLAT CABLE

Figure 34.
The basic trunk-dropline topology uses a cable with 2 separate twisted
pairs, one for power and the other for signal. Flat, thick or thin cables can be used
for trunklines or droplines. The distance between the ends of the network
varies with the data rate and the type of cable (see the table below).

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Table 6.
DATA RATE 125 250 500
Kbps Kbps Kbps
Length for main bus with thick cable (“thick - trunk”) 500m 250m 100m

Length for main bus with thin cable (“thin - trunk”) 100m 100m 100m

Length for main bus with flat cable (“flat - trunk”) 420m 200m 75m

Maximum length for 1 branch from the main bus 6m 6m 6m

(“maximum - drop”)
Cumulative length of main bus branches (“cumulative 156 m 78 m 39 m
– drop”)

The following figure shows examples of installations using style connectors.

open-style and also sealed-style connectors.

Figure 35.

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TERMINATION RESISTORS

A termination resistor must be installed at the ends of the network, which has the
aim to reduce possible reflections of the signal in the network, which causes disturbances in
communication, with constant and random stops and eventually total interruption of but the value is
its operation. The termination resistor should be 121ÿ, the most , admitted
common commercial resistor is 120ÿ , and since the power dissipated is minimal, a 1/4W
resistor would be adequate.

Figure 36.

The resistors must be connected between the communication wires (white BR and blue
AZ), at both ends of the network at the points between all those that have the greatest distance
between them, or in the two distribution boxes at the ends of the network.

With the network off, measure the resistance between CANH (white wire) and CANL (blue wire)
which should be approximately 60ÿ , value of the two termination resistors of
120ÿ in parallel.

Figure 37.

Note that this test serves to verify whether the number of terminations is correct, but
does not test whether the position is correct. For this, you must have a network project in
hand where the points where the terminators will be placed are defined.

This test is very useful, as it is much more common than you might think to install
an incorrect number of terminators, which causes irregular network operation.
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POWER SUPPLY

The “PowerTap” has over-current protection for the “thick” cable.

With diode protection it is possible to use several “PowerTaps” thus allowing the
use of several power supplies.

Figure 38.

CONNECTORS AND TERMINALS

The types of connectors typically used in DeviceNet are: sealed and non-
sealed connectors. There are large (“mini-style”) and small (“micro-style”)
pluggable sealed connectors.

Figure 39.
For applications that do not require sealed connectors, the open-style
can be used. Screw connections or clamp connections can be made directly
to the cable if a plug connection is not required.

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Figure 40.

The following figure shows a typical configuration using open type devices.
“open-style”:

Figure 41. “Open-style” termination

The power supply characteristics of a Devicenet network are:

• Thick Cable (Trunk) - 8 A

• Thin Cable (Trunk) - 3 A

• Mini Connectors - 8 A

• Micro Connectors - 3 A

The current limit in a shunt varies depending on its length, as shown in the
following table:

Table 7.
LENGTH OF MAXIMUM CURRENT
DERIVATION
1.5 m 3.0 A
2.3 m 2.0 A
3.0 m 1.5 A
4.5 m 1.0 A
6.0 m 0.75 A

“TAPS” DERIVATIVES

There are several types of “TAPS” taps to be connected to a network of

DeviceNet type. These taps allow you to connect the various elements of the network.
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They are classified as: T-BIND “T-PORT TAP ”; MULTIPLE DEVICE BIND
“DEVICE -PORT” and BOX TYPE MULTIPLE BIND “DEVICEBOX”.

T-PORT TAP “ T-PORT TAP “

The “T-Port” tap connects a single device or a “drop line” tap via a quick-plug
style connector.

Figure 42.

MULTIPLE DEVICE DERIVATION “DEVICE -PORT”

“DevicePort” are sealed components that connect to the “Trunk line” via “drop line”
via quick-disconnect connectors only devices compatible with the DeviceNet
network. There are DevicePorts to connect 4 or 8 devices.

Figure 43.

MULTIPLE DERIVATION BOX TYPE “DEVICEBOX”

“DeviceBox” are passive elements that directly connect devices

DeviceNet on the “Trunk Line” via terminal connections for up to 8 nodes. They have a
removable sealed cover that allows mounting on the machine or on the factory floor.

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Figure 44.

GROUNDING

Grounding is extremely important in a digital network, for this reason the correct
connection must follow the following rule: "The DeviceNet network must be grounded at a
single point, preferably where the network power supply enters, and at this point the shield
wire must be connected to the negative of the source, if there is more than one source, this
connection must be made only at the grounding point".

Ideally, there should be an exclusive ground for instrumentation, if not,

is available use common ground.

As previously mentioned, the DeviceNet network must be grounded at only one point. It is
possible to test a ground connection by opening the ground connection and measuring the
resistance between the black wire (V-) and the bare wire (shield), which should be in the order of Mÿ.

If the result of this operation is 0ÿ, it means that there are other grounded points, in
this case check if the shield wires are correctly installed with the shrink tube and the cable
shield also insulated.

After carrying out the above tests, measure the voltage differential at several points in the network.
between shield and V-, with the positive of the meter on the shield and the negative on V-, this
voltage must have values from the table below:

Table 8.
Drain voltage/V- Ideal Acceptable

Minimum -4.0V -5.0V

Maximum 0.3V 1.0V

If there is any point with values that are not within this range, some
tests can be done as follows:

• Check that the shield and V- are connected to each other and the network is grounded at
the source;

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• Check that there are no open and/or shorted sections of the shield wire;

Note 1: With the grid grounded at the source and connected at this point to V-, the shield
voltage will always be zero or negative in relation to V- due to the offset caused by the voltage
drop in the black wire of V-.

Note 2: We recommend that DeviceNet cables be routed separately from

power cables, and do not use the same tray or conduits.

GROUNDING OF THE SHIELD

After the previous tests, the drain wire must be connected to the negative “V-” of the network
at the “-” terminal of the power supply that will energize the network. Then both “V-” and
“-” must be connected to the plant instrumentation grounding system on a rod independent of
the electrical grounding, but different rods can be interconnected by potential equalization bus.

Figure 45.

CHECKING SHIELD INSULATION

At the end of the installation, the insulation of the mesh and drain in relation to ground
(> 1Mÿ) must be checked .

Figure 46.

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MULTIPLE SOURCES:

When the DeviceNet network uses two or more sources, only one of them must
have the negative grounded on a rod together with the network drain wire.

Figure 47.

Please note that in this case the power supplies must not be connected to
parallel, interrupt the positive, so that there are not two sources in one section.

CAUTION! We repeat: it is extremely important that the grounding mesh is grounded only at a single
point near the power supply of the network. It is advisable to disconnect the drain connection from the
negative terminal of the source whenever there is maneuvering of the network cable or
maintenance of the instruments to check that the insulation of the drain wire is not grounded at any
other point of the network, since maneuvering of the cables can often break the insulation of the cable
connecting the mesh to grounded conduits or gutters.

ADDRESSING THE INSTRUMENT ON THE DEVICENET NETWORK:

Equipment addressing can be done by hardware or software, being

that the default address for new equipment is 63.

Indicating the addressing in the network flowchart is very important to facilitate replacement
if any equipment requires maintenance. Incorrectly addressing the module in the DeviceNet network
will cause the scanner to fail.

Normally when addressing is done by hardware, dip switches (S1 to S6) are used for the address
and (S7 and S8) for the speed rate, and all possible combinations for the addresses are considered.

It is recommended that the node referring to the DeviceNet address be described on the module
itself, facilitating its exchange and, if possible, also the dip-switches configured in “ON” and “OFF”.

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Figure 48.

DEVICENET DEVICE INDICATORS

Although a DeviceNet product is not required to have indicators, if that product

have indicators, must comply with the DeviceNet specification. It is
recommended that a Module Status LED or a Network Status LED, or a combination
of both, be included.

The indicator(s) consist of a bicolor LED (green/red) that can have

combinations of on, off and flashing.

The Module Status LED indicates whether the device has power and is operating
properly.

The Network Status LED indicates the status of the communication link.

Figure 49.

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DEVICENET PROJECT DETAILS

Installing networks without a pre-design usually leads to disappointing

operational results, when they work at all. It is almost always very difficult to
correct them, as the basic fundamentals have usually not been observed.

All future functionality of the DeviceNet network begins with a preliminary and
detailed design showing all the instruments belonging to the network with their
respective model, tagging, physical location as well as input and output of the
network cable and its derivations.

The network flowchart is the main tool for safe, smooth maintenance
and quickly, thus avoiding hours of production being interrupted due to the lack of this document.

This flowchart should contain:

• Topology.

• Indication of instruments and interconnections.

• Addressing the instrument on the DeviceNet network.

• Cable length.

• Location of termination resistors.

• Current in Various Sections of the Network.

• Source Positioning.

• Grid Grounding Point.

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Figure 50.

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INDICATION OF INSTRUMENTS AND INTERCONNECTIONS

It is essential that the indication of the connections of the equipment that make up the
DeviceNet network is fully detailed in the network flowchart, as it facilitates the location of the equipment for
future maintenance, enabling the replacement of the damaged instrument or connection.

The branch modules described in the network flowchart must be illustrated with
all leads and instruments, even those not in use.

We recommend that the main cable (trunk) be correctly identified at the

module inputs and outputs to facilitate its location.

Figure 51.

CABLE LENGTH

The length of the DeviceNet network cables must be described in the network flowchart.
network, as with this information it is possible to determine the voltage drop of the
instruments, observing the length limits according to the type of cable.

TRUNK LENGTH

The trunk line of the DeviceNet network can be implemented with the thick cable with its
maximum length limited depending on the communication rate.

It is also possible to use a Flat cable, but it should be avoided routing it near
other cables that could generate electromagnetic induction.

The illustration below represents the analysis of the project, which totaled
210m as the length of the main busbar, demonstrating that it will be possible to use

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initially with two speeds: 125 Kbits/s (normally the most used) and 250 Kbits/s, as
they allow distances of 500 and 250m respectively.

Figure 52.

LENGTH OF LEADS (THIN CABLE)

The maximum length for each branch is 6m, regardless of the rate of
communication selected for the network, which our example project is meeting.

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Figure 53.

As the sum of all derivations resulted in 44m, this means that it will be possible to use speeds
of 125 Kbits/s (normally the most used) and 250 Kbits/s, as they allow distances of 156 and 78m
respectively, for the total of derivations in a network.

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SIZING VOLTAGE DROP ACROSS THE NETWORK

In a Devicenet network, an important consideration to note is that the drop
voltage drop along the V- conductor of the network must not exceed 5V, therefore it is
important to calculate this drop mainly based on:

• Point where the source is installed

• Current consumption of each device

• Distance from the source of each device

• Type of cable used in the trunk

• Number of taps connected

Assuming that the source can be installed at the end of the trunk or in
any other point of the same, it is possible to have one, two or more segments to be analyzed,
as shown in the illustration below.

Figure 54. Power supply installed at the end of the network

Figure 55. Source installed at any point in the network

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Another important feature is that the current that will power the network devices
must not exceed the limits of each type of cable depending on the distances between the
devices.

CALCULATION OF VOLTAGE DROP ALONG THE NETWORK

To calculate the voltage drop across the network, the following equation must be used:

SUM {[ (Ln x Rc) + (Nt x 0.005)] x In} ÿ 4.65V

Being:

Term Description

Ln L = Distance in (m) between the device and the power supply, excluding
derivations (drop line).
n = The number of the device being evaluated, starting with 1 for the
device closest to the source and incrementing by 1 for each next device

RC Thick cable = 0.015 ÿ/m

Thin cable = 0.069 ÿ/m
Flat cable (Flat) = 0.019 ÿ/m

Nt The number of taps between the source and the device being evaluated.
For example: • For the device
closest to the source, this number is 1. • When the device
has only one tap between it and the source,
this number is 2.

• When 10 devices exist between what is being evaluated and the

source, this number is 11.
For devices connected via Device box or Device port type shunts, the
shunt should be treated as a single shunt. The current from all devices
connected to one of these shunts should be added together and used
only once in the equation.

0.005 Nominal contact resistance, used for any connection to the trunk

In I = Current drawn from the cable by the device. The current of all
devices connected to a Device box or Device port type branch must be
added together, and count this branch as only 1.
n = The number of the device being evaluated, starting with 1 for the
device closest to the source and incrementing by 1 for each next device
being evaluated.

4.65V The maximum allowable voltage drop in the trunk. This is the total
voltage drop in the cable which is 5.00 V minus 0.35 V reserved for
voltage drop in the taps.

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EXAMPLE OF CALCULATION FOR A SYSTEM WITH POWER SUPPLY INSTALLED AT THE END OF THE

SEGMENT:

The following example considers 4 devices connected in a trunk with thick cable,
whose distances are shown in the following figure, both in meters (m) and feet (ft), with a
source installed at the end of the segment.

Figure 56.

Calculate the voltage drop for each device using the basic equation:

SUM {[ (Ln x Rc) + (Nt x 0.005)] x In} ÿ 4.65V

D1 [ (15 x 0.015) + (1 x 0.005) ] x 1.00 = 0.23V

D2 [ (30 x 0.015) + (2 x 0.005) ] x 0.50 = 0.23V

D3 [ (122 x 0.015) + (3 x 0.005) ] x 0.50 = 0.92V

D4 [ (244 x 0.015) + (4 x 0.005) ] x 0.25 = 0.92V

Adding the individual voltage drop of the devices, to obtain the total system drop, we
will have:

0.23 + 0.23 + 0.92 + 0.92 = 2.30V

CONCLUSION: Since the total voltage drop did not exceed 4.65V, the system will operate
normally (2.30V < 4.65V)

The load percentage can be calculated by dividing the value found by the maximum
voltage drop:

%LOAD = 2.30V / 4.65 = 49.5%

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EXAMPLE OF CALCULATION FOR A SYSTEM WITH A POWER SUPPLY INSTALLED IN THE MIDDLE OF THE NETWORK

The following example considers 6 devices connected in a trunk with thick

cable, whose distances are shown in the following figure, both in meters (m) and in
feet (ft), with a source installed in the middle of the segment, meaning that for the
purpose of calculating the voltage drop, we will consider two segments.

Figure 57.
Whenever the source is installed in the middle of the network, try to place the devices with
greater consumption close to the source, when possible.

Therefore, to calculate this example, it is necessary to divide it into two sections and
each section is calculated individually.

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DEVICENET EXERCISE
Calculate the voltage drop across the network for the following installation:

Consider:

• Source connected to the terminal close to the MASTER device

• MASTER = 90mA

• FLEX_I_O = 200mA

• INDUCTIVE_SENS = 60mA

• PHOTO = 70mA

• DRIVE = 40mA

• KFD = 100mA

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DATA EXCHANGE METHODS IN COMMUNICATION

DeviceNet defines two different types of messaging. They are called

I/O Message and Explicit Message.

I/O MESSAGES

I/O messages are time-critical and control-oriented data.

They provide a dedicated, specific communication path between a producing application and one or
more consuming applications. They are exchanged over single or multiple connections and typically
use high-priority identifiers. I/O messages do not contain any protocol in the 8-byte data field. The only
exception is for fragmented I/O messages where one byte is used for protocol fragmentation. The
meaning of the message is contained in the connection ID (CAN identifier). Before messages can be sent
using these IDs, both the sending and receiving devices must be configured. The configurations
contain the source and destination object attribute addresses for the producer and consumer of the data.

CYCLIC DATA EXCHANGE METHOD

In this method the data is sent cyclically by the device based on the configured time value. The
data is independently received cyclically from the device sending the data.

Unnecessary traffic and packet processing are reduced. Instead of a temperature or analog
input block being “scanned” dozens of times each second, it can be set to report its data on a regular
basis consistent with the rate of change it can sense. A temperature sensor in a slow PID loop with a 500
ms update time could have its rate set cyclically at 500 ms.

Not only would it preserve bandwidth to more quickly sense critical I/O data changes, it would also be
more accurate.

ALLEN-BRADLEY Pan elView 550

ALLEN-BRADLEY Pan elView 550

7 8 9
7 8 9

4 5 6
4 5 6

11 2 3
1 2 3

. 0 -
. 00 -

<
- < <-----------------'
- - <-----------------'
-

F1 F2 F3 F4 F5 ^
F1 F2 F3 F4 F5 ^
< >
< >
F1 v
F6 F7 F8 F9
0 F1 v
F6 F7 F8 F9
0

every 100ms

every 5ms every 2000ms

Figure 58.

Devices produce data at a user-configurable rate. The transfer

Cyclic is efficient because data is transferred at a rate appropriate for the device/
application.

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STATE CHANGE DATA EXCHANGE METHOD

In this method, data is sent by the device based on the detection of any change in the value of
the input data. The data is independently received based on the change in state of the device sending the
data. To be safe, the consumer device must know that the producer is still alive and active.
DeviceNet provides a “heartbeat” to the device.

Devices send data whenever they change or “heartbeat.”

expires. This serves to keep the connection alive and lets the consumer know that their data source has
no faults in some way. The minimum “heartbeat” time inherently prevents noisy nodes from
dominating the network.

ALLEN-B RADLEY PanelView 550

7 89

4 56

11 23

. 0 -

<
- <---------- ----- --'
-

F1 F2 F3 F4 F5 ^
< >

F1
F6 F7 F8 F9 v
0

Figure 59.

Because the device generates the heartbeat, the controller is not tasked with sending a request
periodically, just to make sure the device is there. This becomes more efficient in the case of multicast.

This method is efficient because:

• significantly reduces network traffic

• resources are not wasted processing old data

POLLING DATA EXCHANGE METHOD

In this method, data is sent by the device in response to data received. In Polled mode, the Master
“Scanner” sends a “Poll” command directly to a specific slave (point-to-point). The Master “Scanner”
must transmit a separate Poll command to each of its slaves that are being requested. The requested slave
will return the input data.

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ALLEN-BRADLEY Pan elV i ew 550

7 8 9

4 5 6

11 2 3

. 0 -

<
- <---
-' <---
------
------
------
-------- -'
-

^
F1 F2 F3 F4 F5
< >

F1
F6 F7 F8 F9 v
0

Figure 60.
When devices receive data (usually outputs) they immediately send
your data (usually inputs).

EXPLICIT MESSAGES

Explicit messages provide multi-cast, peer-to-peer communication between

two devices. They provide the typical question/answer communication in a network
used for node and configuration troubleshooting. Explicit messages typically use
low-priority identifiers and contain the specific meaning of the message in the data
field. This includes the service to be performed and the specific address attribute of
the object.

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STANDARD: FIELDBUS FOUNDATION

FIELDBUS is currently the technological transition of industrial

automation, mainly in the area of process control.
Technology
Dominant

Pneumatic Analog Digital Fieldbus

1940 1960 1980 2000

Team

Figure 61.
FIELDBUS is a bidirectional digital communication system (Figure) that allows
the networking of multiple instruments directly in the field, performing process control
and monitoring functions and operating stations (HMI) through supervisory
software (Figure).

STATION OF STATION OF
OPERATION MAINTENANCE

DPT + PID FCV TT PT

Figure 62.

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MICROSOFT NETWORK (LAN)

Foundation Fieldbus in
joint operation to
Supervisory Systems

FIELDBUS FOUNDATION

FIELD
DPT101 PT101 FCV101 DPT102 PT102 FCV102

Figure 63.
Next, we will analyze the project details using the FIELDBUS protocol
developed by the Fieldbus Foundation and standardized by ISA-The International
Society for Measurement and Control for the automation of Process Plants.

The following figure illustrates an application example for FIELDBUS networks in

process control.

Fieldbus

Process
P

L
Automation
and

Supervision Systems
F

Figure 64.

The Foundation Fieldbus protocol was developed based on the ISO/OSI

standard, although it does not contain all its levels, we can initially divide it into
physical level (“Physical Layer” - which deals with the interconnection techniques of the instrum

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software (“Communication Stack” - which deals with digital communication

between equipment).

FIELDBUS FOUNDATION
OSI MODEL FIELDBUS MODEL

LAYER LAYER
USER USER

MESSAGE SPECIFIC
FIELDBUS
APPLICATION LAYER
SUBLAYER OF
FIELDBUS ACCESS

PRESENTATION LAYER
“STACK” OF
SESSION LAYER
COMMUNICATION
LAYER OF
TRANSPORT
NETWORK LAYER

LINK LAYER LINK LAYER

DATA DATA
PHYSICAL LAYER PHYSICAL LAYER PHYSICAL LAYER

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BASIC STRUCTURE

In the study of the basic structure (physical level) we will be analyzing the types
of possible connections (wiring, coaxial cables, optical or radio), connections,
terminators, electrical characteristics, etc... specified by the FIELDBUS FOUNDATION
PHYSICAL LAYER PROFILE SPECIFICATION, Document FF-94-816, August 28,1995.

There are two subsystems at the physical level that enable integration with Foundation
FIELDBUS:

• H1 (31.25 Kbit/s) to connect field equipment, with bus power supply, intrinsically
safe option and max. 1900 meters.

• HSE (100 Mbit/s or 1Gbit/s - High Speed Ethernet) allowing integration between
high-speed controllers, such as PLCs, using Ethernet with TCP/IP protocol
or other commercial protocol and use of Switches or Routers
HSE… High Speed FF Network CORPORATE ETHERNET
• 100 Mbits/s or 1 Gbits/s
• Ethernet with TCP/IP protocol.
• Use of Switches or Routers
SERVER GATEWAY

HSE ETHERNET

H1… Low speed FF network

BRIDGE SCADA PLC PLC
• 31.25 Kbps
• Replace 4 to 20 mA
• 2 - 32 Devices H1
• Food & Communication
• Intrinsically Safe
• Twisted pair
• size of 1900 m

ANALYZER

Figure 65.

The ANSI/ISA-S50.02-1992 Standard, approved on May 17, 1994 - “Fieldbus Standard for Use
in Industrial Control Systems Part 2: Physical Layer Specification and Service Definition” deals with
the physical means for performing interconnections and the main items are:

• digital-only data transmission

• self-clocking

• two-way communication

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• Manchester code

• voltage modulation (parallel coupling)

• transmission speeds of 31.25 kb/s, 100 Mb/s

• non-energized bus, not intrinsically safe

• powered bus, not intrinsically safe

• bus without power, intrinsically safe

• intrinsically safe, powered bus

The following figure shows a FIELDBUS segment and some of its main features.
components.

Line Drawing Representation of Simple Fieldbus Segment

1900M Max.

Fieldbus Segment BUS

Terminator Terminator

+
Signal Control or
Isolation Monitoring
Circuit Device
-

Field Devices
Fieldbus
Power Supply
Figure 66.

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NUMBER MAX. SPUR

OF ELEMENTS LENGTH (m)

25-32 0
19-24 30
15-18 60
13-14 90
01-12 120

BUS TOTAL LENGTH

(TRUNK + SPURS) <1900m

Figure 67.

ENERGY DISTRIBUTION
The power supply of FIELDBUS equipment can be optionally provided
through the same communication conductors or separately; an instrument with separate
power supply can be connected to another instrument with power supply and
communication on the same pair of wires.

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RULES

At a speed of 31.25 kb/s, the standard determines, among others, the following rules:

1. A FIELDBUS instrument must be able to communicate between the following

equipment numbers:

• between 2 and 32 instruments in a non-intrinsically safe connection and separate

power supply from the communication wiring;

• between 2 and 6 instruments powered by the same communication wiring in an

intrinsically safe connection;

• between 1 and 12 instruments powered by the same communication wiring

in a connection without intrinsic safety.

Note: This rule does not prevent the connection of more instruments than specified,
these numbers were achieved taking into account the consumption of 9 mA +/- 1 mA,
with a supply voltage of 24 VDC and intrinsic safety barriers with 11 to 21 VDC output
and 80 mA maximum current for instruments located in the hazardous area.

2. A bus loaded with the maximum number of instruments at speed

31.25 kb/s must not have a length greater than 1,900 m between the sum of the
trunk sections and all the spurs;

Note: this rule does not prevent the use of longer lengths as long as the
electrical characteristics of the equipment are respected.

3. The maximum number of repeaters for waveform regeneration between two

instruments cannot exceed 4 (four) (see Figure);

PHYSICAL LAYER

DISTANCE CAN BE INCREASED WITH REPEARTERS

MAXIMUM = 4

1,900 M 1.900 M 1.900 M 1.900 M 1.900M

REP1 REP2 REP3 REP4 Terminator

Figure 68.

4. A FIELDBUS system must be able to continue operating while a

instrument is being connected or disconnected;

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5. Failures of any communication element or derivation (with the exception of short circuit or low
impedance) should not affect communication for more than 1 ms;

6. Polarity must be respected in systems that use twisted pairs, their conductors must be identified
and this polarization must be maintained at all connection points;

7. In systems with redundant physical media:

• each channel must meet the network configuration rules;

• there must not be a non-redundant segment between two segments

redundant;

• repeaters must also be redundant;

• the channel numbers must be maintained in the FIELDBUS, i.e. the channels of the
FIELDBUS must have the same numbers as the physical channels.

8. The shielding of the cables should not be used as energy conductors.

Below are some electrical specifications for FIELDBUS systems:

• A device can optionally receive power through signal conductors or

by separate conductors;

• A device can be certified as intrinsically safe by receiving power from both the signal
conductors and separate conductors;

• Separately powered equipment can be connected to powered equipment by the same

signal conductor.

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Here are presented the main components that are part of a FF network.

HOST DEVICES (SERVER) is a device connected to the Fieldbus system that can
configure, monitor and interact with the process without the need to remain in the field, and
can be a SDCD (Distributed Digital Control System), a SCADA (Supervisory Control and
Data Acquisition) system or a common microcomputer [19].

A REPEATER is a device with an energized or unenergized bus, used to extend

a Fieldbus segment.

As discussed in the introduction to the Physical Level, a maximum of four repeaters or active
couplers can be used between any two devices in a Fieldbus network segment. Using four repeaters, the
distance between any segment is 9500 m.

1,900 M 1,900 M 1,900 M 1,900 M

REP1 REP2 REP3 REP4

Figure 69.
BRIDGE is a device with a powered or unpowered bus, used to connect Fieldbus
segments of different speeds in order to form an extensive network. The figure
shows an application for Bridge.

Bridges are normally used as interfaces between the HSE (fast Ethernet – 100Mbits/s)
and H1 (low-speed Fieldbus – 31.25 kbits/s) levels of an application.

HSE (High Speed Ethernet)

Bridge

31.25 kbit/s Fieldbus

31.25 kbit/s Fieldbus

Figure 70. Bridge in a Fieldbus system

GATEWAY is a device with a powered or unpowered bus, used to connect one or

more segments in other types of communication protocols such as ETHERNET, RS
232, MODBUS, etc.

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MODBUS PC BUS

LC700
FIELDBUS
CARD
FIELDBUS H1

Figure 71.

SOURCE REDUNDANCY

In the event of a failure of one of the sources, the other will automatically come into operation.
Only one PSI should have the terminator connected, or a BT terminator can be used.

PS PSI BT

PS PSI

Terminator Connection
Figure 72.

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P
S
3
0
2 N
PSI 302 BT302
L

BT302

PSI 302

P
S
3
0
2 N
L

Figure 73.

+
EXTERNAL TERMINATOR
+

P
S
3
0
2 N
PSI
302 BT302
L

BT302

PSI
302

P
S
3
0
2 N
L

Figure 74.

The most commonly used equipment developed to operate as instruments

Fieldbus, are related below:

PCI = Process Controller Fieldbus Interface;

DFI = Distributed Field Interface;

PS = Power supply;

PSI = Bus filter;

SB = Intrinsic Safety Barrier;

BT = Fieldbus Terminator;

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LD = Pressure Transmitter;

TT = Temperature Transmitter;

FI = Fieldbus to Current Converter;

IF = Current to Fieldbus Converter;

FP = Pneumatic to Filedbus Converter;

FY = Fieldbus Positioner;

DISTRIBUTED FIELD INTERFACE – DFI is the key interface element in a field control
system, combining communication capabilities with direct access to advanced control
inputs and outputs for continuous and discrete applications. Highly scalable, it can be
used in small systems or highly complex plants.

It works as a Bridge between H1–H1, H1–HSE (High Speed Ethernet) or H1–HSE–

H1, and also for H1 bus, managing communication on each channel. They allow the
execution of several functional blocks, including new flexible blocks, programmed with
IEC 61131 language (Ladder, SFC, STL, Grafcet, etc.).

The figure shows an illustration of a Distributed Field Interface – DFI for

Fieldbus Foundation (DFI302).

Figure 75. Distributed field interface

It works as a Gateway between HSE or H1 and other protocols other than FF, such as
Profibus, Devicenet, etc. The figure shows the use of DFI as a Gateway.

Figure 76. DFI as gateway

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CABLES

According to the requirements of the ISA-S50.02 standard, the cable used

to connect FIELDBUS equipment with the 31.25 Kbit/s voltage mode can be a simple
twisted pair of wires with its shielding meeting the following minimum requirements
(at 25 ºC):

• Z0 in fr (31.25 KHz) = 100 ÿ ± 20%;

• Maximum attenuation at 1.25 fr (39 KHz) = 3.0 dB/Km;

• Maximum unbalanced shield capacitance = 2 nF/Km;

• Maximum DC resistance (per conductor) = 22 ÿ/Km;

• Maximum propagation delay between 0.25 fr and 1.25 fr = 1.7 µs/Km;

• Conductor cross-sectional area (gauge) = nominal 0.8 mm2 (#18 AWG);

• Minimum shielding coverage must be greater than or equal to 90%.

For new installations we must specify shielded twisted pair cables.

type A, other cables can be used but respecting the limitations in the table below,
such as multiple cables with twisted pairs with a general shield (called type B cable).

The least recommended type of cable is the single or multiple twisted pair cable
without any shielding (called type C cable).

The least recommended type of cable is the multi-conductor cable without pairs.
braided (called type D cable) and general shielding.

Below is the table of specifications for cable types (at 25 ºC):

Table 9.
Parameters Conditions Type “A” Type “B” Type “C” Type “D”
** **
fr (31.25 KHz) 100 ± 20 100 ± 30
Characteristic impedance, Z0, ÿ

Maximum DC by driver 22 56 132 20

resistance, ÿ/km

Maximum attenuation, 1.25 fr (39 kHz) 3.0 5.0 8.0 8.0

dB/km

Nominal cross- 0.8 0.32 0.13 1.25

sectional area of the conductor
(#18 AWG) (#22 AWG) (#26 AWG) (#16 AWG)
(gauge), mm2
** **
Max unbalanced 1 meter long 2 2
capacitance, pF **
not specified
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Notes:

Other cable types that meet or exceed the specifications may be used.
Cables with improved specifications may enable longer bus lengths and/or
greater immunity to interference. Conversely, cables with lower specifications may
result in length limitations for both trunks and spurs, but cables that do not meet
RFI/EMI compliance requirements are not acceptable.

For intrinsic safety applications, the inductance-to-resistance (L/R) ratio must be

less than the limit specified by the local regulatory agency.

FOUNDATION TECHNOLOGY
USER

31.25 kbit/s FIELDBUS WIRING LAYER

CONTROL ROOM COMMUNICATION

“STACK”

EQUIPMENT
PHYSICAL LAYER

Trunk Junction
box

Spurs

Cable Length = Trunk Length + All Spur Lengths

Maximum Length = 1900 meters with “Type A”Cable
Figure 77. Cables used in FIELDBUS

Table 10. Typical bus and branch lengths

Cable type Distance (m)
THE 1900

B 1200

W 400

D 200

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CHARACTERISTICS OF GRID-POWERED EQUIPMENT FOR THE

31.25 KBIT/S VOLTAGE MODE

Operating voltage 9.0 to 32.0 V DC

Maximum voltage 35 V

Maximum rate of change of quiescent (non-transmitting) current; 1.0 mA/ms

this requirement does not apply in the first 10 ms after connecting
the equipment to an operating network or in the first 10 ms after
energizing the network.

Maximum current; this requirement is set during the interval of 100 Quiescent current plus 10 mA
µs to 10 ms after the equipment is connected to an operating
network or 100 µs to 10 ms after the network is energized.
Fieldbus
Messages

Voltage

Time

REQUIREMENTS FOR POWER SUPPLY OF MAINS FOR VOLTAGE MODE

FROM 31.25 KBIT/S

Output voltage, not intrinsically safe ÿ 32 V DC

Output voltage, intrinsically safe (IS) depends on the barrier range

Non-intrinsically safe output impedance, measured within the ÿ 3 Kÿ

frequency range 0.25 fr to 1.25 fr

Output impedance, intrinsically safe, measured within the frequency

ÿ 400 Kÿ (Intrinsically safe power
range 0.25 fr to 1.25 fr
includes an intrinsically safe barrier).

A FIELDBUS device that includes the 31.25 Kbit/s voltage mode will be able to
to operate within a voltage range of 9 V to 32 V DC between the two conductors including ripple. The
equipment may be subjected to a maximum voltage of 35 V DC without causing damage.

NOTE: For intrinsically safe systems the operating voltage may be limited
by certification requirements. In this case the power source will be located at the

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safe area and its output voltage will be attenuated by a safety barrier or equivalent
component.

ELECTRICAL INSULATION

All FIELDBUS equipment that uses wire conductors, either for separate power
supply or for power supply through the communication signal conductors, must
provide low-frequency isolation between ground, bus cable, and the
equipment. This must be done by isolating the entire equipment from ground or by
using a transformer, optocoupler, or other isolating component between the
trunk and the equipment.

A power supply combined with a communication element will not require

electrical isolation.

For shielded cables, the insulation impedance measured between the FIELDBUS
cable shield and the FIELDBUS equipment ground must be greater than 250 Kÿ at all
frequencies below 63 Hz.

The maximum unbalanced capacitance to ground of both input terminals

a device should not exceed 250 pF.

CONNECTORS

Connectors for cables, if used, may be quick-release or traditional

connectors. Terminations in the field should not be made directly at the instrument
terminals but rather through connectors in termination boxes.

To
Fieldbus
H1 Card Fieldbus
Molded Cordset with Terminator
Junction Junction
Box
4-Prong Connector Box

Device
Receptacle

Figure 78.

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Figure 79.

TERMINATORS

A terminator must be at both ends of the trunk cable, connected from one signal conductor to
the other. No connections should be made between the terminator and the cable shield.

The terminator can be implemented internally to a field box (Junction Box).

The terminator impedance value should be 100 ÿ ± 20% within the frequency range 0.25 fr to
1.25 fr (7.8 KHz to 39 KHz). This value is approximately the average value of the cable's characteristic
impedance at the operating frequencies and is chosen to minimize reflections in the transmission
line.

Schematic Representation of Balanced Transmission Line

Near-End Far-End
Terminator Terminator

Field Devices
Fieldbus
Power
Suply

Signal 100 ÿ 100 ÿ

20 V + Isolation
Name Circuit
-
1 µF 1 µF

1900M Max.

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The direct current flow through the terminator must not exceed 100 µA. The terminator
must not be polarized.

All terminators used in intrinsically safe applications must meet

isolation and distancing needs (required for IS approval).

It is accepted for the functions of power supply, safety barriers and

terminators to combine them in various ways (provided that the equivalent
impedance meets the requirements of the ISA-S50.02 standard).

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SHIELDING RULES

To meet noise immunity requirements, it is necessary to ensure the continuity of

shielding through cabling, connectors and couplers, complying with the following rules:

The cable shield coverage must be greater than 90% of the total cable length;

The shielding must completely cover the electrical circuits, including connectors, couplers and
splices.

GROUNDING RULES

To meet noise immunity requirements, it is necessary to ensure the continuity of

shielding through cabling, connectors and couplers, complying with the following rules:

a) the cable shield coverage must be greater than 90% of the total cable length.

b) the shielding must completely cover the electrical circuits through also
of connectors, etc.

NOTE: Failure to follow these rules may degrade noise immunity.

The grounding for a FF system must be permanently connected to earth

through a sufficiently low impedance and current-carrying capacity to prevent voltage spikes, which
could result in danger to connected equipment or people.

FF equipment cannot connect any conductor of the twisted pair to ground at any point in the network.

It is standard practice for a FF bus cable shield to be effectively grounded at a single point
along the length of the cable. For this reason FF equipment must have DC isolation from the cable shield to
ground.

Figure 80.

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The shield must be grounded at the negative terminal of the power supply:
Shield

PS
PSI BT
24 V

Trunk and branch

shields must be connected.
Figure 81.
Only one shield can be connected:
Shield

PS ISB BT

Fieldbus

Classified area
Figure 82.
INTRINSIC SAFETY

Intrinsic safety barriers must have impedance greater than 400 ÿ in

any frequency in the range of 7.8 KHz to 39 KHz, this specification applies to
intrinsic safety barriers of the separate equipment type or incorporated
internally in power supplies.

Within the operating voltage range of the intrinsic safety barrier (within the range
7.8-39 KHz) the measured capacitance from the positive terminal (hazardous side) to
ground shall not be greater than 250 pF of the measured capacitance from the
negative terminal (hazardous side) to ground.

An intrinsically safe barrier shall not be separated from the terminator by more
than 100 m (Error! Reference source not found.). The barrier may present an
impedance of 400 ÿ at the operating frequency and the resistance of the terminator
shall be sufficiently low so that when placed in parallel with the barrier impedance, the
equivalent impedance shall be entirely resistive.

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HAZARDOUS AREA
TERMINATOR

INTRINSIC
SAFETY BARRIER
Inside Junction Box

BUS TERMINATOR

Figure 83. Intrinsic Safety

The ANSI / ISA - S5.02 - 1992 standard establishes that one to four
instruments (after the Intrinsic Safety Barriers) can be connected in hazardous areas
and two more devices in safe areas on the same bus.

Hazardous Area

Single
IS Barrier
T
H1 Segment
T

Non-IS
Devices
Figure 84.

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DETAILING PROJECTS WITH FIELDBUS

An important aspect in designing a Foundation Fieldbus project is determining how the

equipment that will be part of the network will be installed.

Several topologies can be applied in Fieldbus projects. The figure illustrates four topologies.
In order to simplify and make the graphics clearer, the power supplies and terminators have been omitted
from them.

HSE LEVEL PLANT

BOX OF
JUNCTION
BRIDGE

LEVEL H1

END - END LINE WITH BRANCHES POINT TO POINT TREE

Figure 85. Possible FIELDBUS connection topologies

FIELDBUS HSE LEVEL

TERMINATOR
BRIDGE

NETWORK (TRUNK)

BRANCH

Figure 86. NETWORK TOPOLOGY WITH BRANCHES

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FIELDBUS HSE LEVEL

Termination FIELDBUS LEVEL H1

here

BRIDGE
Figure 87. POINT-TO-POINT TOPOLOGY

BOX OF BOX OF
JOINTS JOINTS

LEVEL H1 LEVEL H1
TERMINATOR

Figure 88. TREE TOPOLOGY

FLOW RATE
XMTR VALVE

SOURCE

FIELDBUS

TERMINATOR TERMINATOR
LEVEL
XMTR

BOX OF
JUNCTION LEVEL
100ÿ
XMTR

Figure 89. EXAMPLE OF TREE TOPOLOGY

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BOX OF BOX OF
JOINTS JOINTS

Single or multi-pair cables

LEVEL H1 LEVEL H1

Figure 90. END TO END TOPOLOGY

Use only one of the electrical conductors for “input” and “output” of the cables, for
maintenance or replacement of the instrument without interrupting the network.

Figure 91.

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Therefore, the maximum distances allowed between the equipment must be

considered, that is, the plan where the project will be carried out must be at hand to
determine the best points for installing the equipment in order to optimize the length of
the busbar (trunk) and the derivations (spurs) as seen in the figure.

H1

<60m

<90m

<120m
<1m
<1m <1m

This segment has 11 devices. Each

spur with one device must be <120
meters, the spur with 2 devices must be
<90 meters, and the spur with 3 devices
must be less than 60 meters.

Figure 92.
In addition, other characteristics must also be considered, such as: maximum number
of devices connected to the same network (a limiting factor may be the power supply that
must supply all transmitters, if the bus is energized), the topology used in the
implementation of the equipment and the elements that will constitute the fieldbus network
together with the equipment (devices that allow ease and agility when some type of
maintenance is requested with a certain piece of equipment, such as field boxes).

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Table 11.
Total 1 device per 2 devices per 3 devices per 4 devices per
devices in the Spur Spur Spur Spur
segment

1-12 394 ft. (120 m) 295 ft. (90 m) 197 ft. (60 m) 98 ft. (30 m)
13-14 295 ft. (90 m) 197 ft. (60 m) 98 ft. (30 m) 3 ft. (1 m)
15-18 197 ft. (60 m) 98 ft. (30 m) 3 ft. (1 3 ft. (1
19-24 98 ft. (30 m) 3 ft. (1 m) m) 3 ft. (1 m) m) 3 ft. (1 m)
25-32 3 ft. (1 m) 3 ft. (1 m) 3 ft. (1 m) 3 ft. (1 m)

Another point to be analyzed refers to the use of intrinsic safety barriers.

and equipment redundancy. A preliminary analysis of these characteristics
must be carried out in the system installation environment, aiming at the greatest
possible optimization in terms of equipment installations (number of devices
and length of each bus), if it is necessary to use these resources.
The next sections will cover in greater depth the topologies commonly used in fieldbus
systems as well as the components of a project.

The following figure shows the components of a typical installation:

SOURCE
IMPEDANCE TERMINATOR

PS302 _+ PSI302

PT FT TT FY PT

TERMINATOR

Figure 93.

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SOFTWARE LEVEL

Although the objective of this course is not an in-depth study of the levels of
software, below we will explain some details. We emphasize that for the user all this is transparent and is
handled by the configuration software.

LINK LEVEL (DATA LINK LAYER)

The link level ensures message integrity through two bytes calculated using a polynomial applied to all
bytes of the message and added at the end of the message. This level also controls access to the
transmission medium, determining who can transmit and when. The link level ensures that
data reaches the correct equipment.

The characteristics of this level are:

WAYS TO ACCESS THE NETWORK:

• Token Passing: The Token is the direct way to initiate a transition on the bus.
When it finishes sending messages, the device returns the “Token” to the LAS (Link Active Scheduler).
The LAS transmits the “Token” to the device that requested it, via pre-configuration or via scheduling.

• Immediate Response: The LAS (master) will give an opportunity for a station to respond
with a message.

• Token Request: A device requests a Token using a code in one of the responses it transmitted to the bus. The
LAS receives this request and sends a “Token” to the device when there is time available in the aperiodic
scheduling phases.

PRODUCER/CONSUMER MODEL: in which a device can produce or consume variables that are
transmitted over the network using the immediate response network access model. The producer places
the variables in Buffers and any station can access this data. With just one transaction, data can be
transmitted to all devices that need this data. This model is the most efficient way to transfer data between
multiple users. A controller consumes the process variable produced by the sensor, and produces the output
consumed by the actuator.

SCALING TO SUPPORT TIME-CRITICAL APPLICATIONS:

LAS will coordinate the time required for each transaction on the network, ensuring the
data exchange period.

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TIME SYNCHRONIZATION

There is a mechanism to ensure a network time reference to achieve

bus synchronization and process activities.

ADDRESSING

It can be used to address a group of stations, one station or even a

variable. This addressing allows for optimization of access to messages.

MACRO CYCLE

An important aspect when working with Fieldbus systems is the time it takes
for all devices in the line to publish control and monitoring parameters for a process.
This time should be minimized as much as possible because it can compromise
the update time of the links between the functional blocks operating in the control
loop in relation to the speed of the process.

Links are updated every MACRO CYCLE (MC) and this time may vary.
depending on the type of instrument and its parameters for publication. In a
project, the MC time must be checked to compare it with the critical process time and
verify that the MC of this bus does not compromise the dynamics of the process.

The cycle time on a Foundation Fieldbus bus is divided into Operational

Traffic (where control information is published), which has a cyclic function, and
Acyclic Traffic (where non-control information is published, such as monitoring
data or actions coming from supervisory software).

30% 70%

Operational Traffic Acyclic Traffic

Figure 94.

The acyclic traffic time can be defined and configured by the user through the
SYSCON software (typical is ÿ 100 msec).

Operational traffic time can be determined by the highest value between:

• the sum of the execution times of the functional blocks of each instrument

• calculation of the number of external links (between instruments) multiplied by 30msec.

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COMMUNICATION STACK

In FF (Fieldbus Foundation) there is the DLL (Data Link Layer) that

controls the transmission of messages on the bus, through a deterministic
organizer, called LAS (Link Active Scheduler), which requests, according to
the scheduling algorithm, each data transfer on the bus. The two types of devices
used in FF are defined as: Basic devices that do not have the capacity to become a
LAS, and LM (Link Master) devices that can become a LAS.

CYCLIC COMMUNICATION (SCHEDULED):

LAS has a list of the data transmission time of all devices that
need to be transmitted cyclically. When a device sends information, the LAS
assembles a communication order message, called CD (Compel Data) for the device
that must communicate. After receiving the CD, the device, which is now
called the producer (publisher), publishes its data to all devices on the bus. The
devices that are configured to receive the data are called consumers (subscribers),
as shown in Figure 3.6. This cyclic communication model, also called producer/
consumer, is normally used to transfer the most important data in a control loop
between devices on the bus.

LAS = Link Active Scheduler

Organizer
CD = Compel Data
the

b
CD (a) Fieldbus
w
LAS

Message

Given to Given to Given to

Producer Consumer Consumer

Figure 95. Model for cyclic communication in FF

UNSCHEDULED COMMUNICATIONS:

All devices on the FF bus have the opportunity to send acyclic messages
between cyclic message transmissions. The LAS of an LM (Link Master) device grants
permission for other devices to communicate by sending a command-type
message called PT (Pass Token) to a device, for example, Device X, as shown in the
figure. Upon receiving the PT, this device can send acyclic data until the time
reserved for token retention ends. Messages can be sent to only one destination or to
multiple destinations (multicast);

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LAS = Link Active Scheduler

Live List
PT = Pass Token
x
and
PT (x) Fieldbus
z
LAS

Message

Given Given

Device x

Figure 96. Model for acyclic communication in FF

LAS OPERATION

The complete operation of a LAS also includes other steps, listed as follows:

• CD Schedule: It is an operation composed of a list of activities that are

scheduled to occur in a cycle, being the LAS's highest priority task. Precisely
at the configured instant, the LAS sends a CD to a specific device on the
network, which will respond by publishing its data.

• Live List Maintenance: The list of all devices on the bus that are
The list of devices that respond to the PT is called the Live List, and new devices
can be added at any time. The LAS periodically sends messages called PN
(Probe Node) to devices not listed in the Live List, and if one of these is
newly connected to the bus, it will respond with a message called PR (Probe
Response), at which point the LAS will add this new device to the Live List.

• Data time synchronization: the LAS periodically sends a broadcast message called
TD (Time Distribution) to all devices, so that they all have exactly the same time
base. This synchronization is essential for cyclic communication.

• Token Passing: This is an operation in which the LAS sends a message defined as PT
(Pass Token) to all devices in the Live List. When the device receives the PT,
acyclic communication is allowed.

• LAS redundancy: Based on the fact that a bus can have multiple LM (Link Master), if
the current LAS fails, one of the other LM will become the LAS and the
network will continue to operate.

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APPLICATION LEVEL

This is where the interface to the equipment's application software is located. Basically
This level defines how to read, write or trigger a task on a remote station. The main task is
to define a syntax for messages, and it also defines how the message should be transmitted:
cyclically, immediately, only once or when requested by the consumer.

Management defines how to initialize the network: assignment of the TAG (symbolic reference
of the equipment in the network), address assignment, time synchronization, scheduling of
transactions in the network or connection of input and output parameters of the
functional blocks. It also controls the operation of adding a new element or removing a
station, continuously monitoring the bus.

USER LEVEL

Defines the mode for accessing information within Fieldbus devices and how
This information can be distributed to other devices on the network.

The basis for the architecture of a Fieldbus device are the functional blocks, the
which perform the tasks required by today's existing applications, such as:

• data acquisition;

• PID control;

• calculations;

• performance.

Every functional block contains an algorithm, a database (inputs and outputs) and a user-
defined name, the block TAG (which must be unique in the user's plant).

Function block parameters are addressed on the Fieldbus via TAG PARAMETER
– NAME. A Fieldbus device will contain a defined number of functional blocks and the
database can be accessed via software.

Blocks can be divided into three types:

• Transducer Block

• Resource Block

• Functional Blocks

The Transducer block allows you to connect function blocks to the input and output functions of
sensors and actuators, containing information such as: calibration date and sensor type.

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The Resource block describes the characteristics of the FF device, such as device
name, manufacturer and serial number, and there is only one resource block in a device.

Functional blocks are blocks available in devices and have parameters.

input and output that can be connected with other blocks on the same or other devices.

FF defines a standard set of nine functional blocks:

1. AI – Analog Input

2. AO – Analog Output

3. B – Bias

4. CS – Control Selector

5. DI – Discrete Input

6. ML – Manual Loader

7. PD – Proportional/Derivative

8. PID – Proportional/Integral/Derivative

9. RA – Ratio

An example of the application of functional blocks is shown in the figure,

representing a PID type control, performed by three devices: a transmitter and a valve, in
addition to an interface called Host (server).

Figure 97. Application of functional blocks in FF instruments

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Functional blocks can be embedded within any of the devices,

in the example the transmitter has an AI block and the valve has two blocks: PID and AO as
shown in the figure.

Figure 98. Connections between FF instrument blocks

Function blocks must be executed precisely at defined intervals and in the proper
sequence of the control system operation. The start of the operating cycle is defined as
Absolute Link Schedule Start Time and the total execution time of a complete cycle is
called the LAS macrocycle.

The following figure shows the diagram with the time and execution moment of each
task of the control system of the example presented. It can be seen that the cycle begins with
the execution of the AI block processing, which is inside the transmitter called device 1,
and that until 20 ms after the beginning of this cycle the bus is available for acyclic
communication. At 20 ms the LAS will send a CD (Compel Data) to the AI block inside the
transmitter, so that it can publish the data from its buffer on the bus. At 30 ms the PID block
will be executed followed by the execution of the PID block at 50 ms.

Assuming the macrocycle is set to 120ms, except for the time when the
LAS commanded the publication of AI data on the bus, the rest of the time the
bus was free for communications and acyclic functions, including during the execution time
of the function blocks.

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Figure 99. Execution times of cyclic and acyclic tasks in FF

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STANDARD: PROFIBUS

Fieldbuses are used today primarily as a communication system for exchanging information between
automation systems and distributed field devices. Thousands of successful applications have proven that the
use of fieldbus technology can save up to 40% in cabling, commissioning and maintenance
costs compared to conventional technology. Only two wires are used to transmit all relevant information
(e.g. I/O data, parameters, diagnostic data, programs and power to field devices). In the past,
manufacturer-specific (incompatible) fieldbuses were often used. Practically all systems in design today are
open.

Profibus was born in 1987 from an association of 21 companies in Germany to develop a digital
fieldbus. Since 1989, a foundation called PNO has promoted the dissemination and control of this open
protocol. In 1995, Profibus International was founded, encompassing 22 entities spread throughout the
world.

THE PROFIBUS FAMILY

PROFIBUS can be used in both high-speed data transmission applications

speed as well as in complex and extensive communication tasks. The PROFIBUS family consists
of three compatible versions.

Profibus is presented as a complete solution (communication and management) to interconnect existing

devices at intermediate and higher levels in an automation system.

These levels are represented in the figure as Field Level and Cell Level. The figure also divides
the field bus level by type: Manufacturing and Process. The division is justified by the difference in data
to be reported by the devices.

In the figure, the “Ex” symbol represents that Profibus is suitable for use in classified areas, also
called areas with explosive atmospheres. These are environments where there is a possibility of explosions
due to the presence of flammable gases and ignition sources.

Profibus DP features gateway devices for lower-level networks, such as AS-I.

PROFIBUS is a leading open standard in Europe (Source: Independent Fieldbus Study

by Consultic) with Siemens, as one of the largest suppliers of automation equipment in the world, as
one of the main users and sponsors, Profibus has

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approximately 20% of the market in Europe, where application areas include manufacturing, process
and building automation and has been standardized by EN 50 170.

Today, all major manufacturers of automation technology offer PROFIBUS interfaces for their
devices.

Figure 100.

• The Profinet protocol is used to connect PLCs and PCs,

using Ethernet as the physical medium and TCP/IP protocols for transport.

• For interconnecting PLCs and input and output devices in general, it is

Profibus DP is presented, using twisted pair cable with RS-485 or fiber optics as the physical
medium.

• For the interconnection of process instruments, a variation of Profibus DP was presented,

Profibus PA, using the MBP or IEC-1158-2 standard as the physical medium, adapting
the power level of the electrical signals to allow their installation in classified areas.

• For ON-OFF sensors and actuators, “gateways” between Profibus-DP and the AS-I protocol
are provided.

At the actuator/sensor level, AS-Interface is the ideal data communication system, since binary data
signals are transmitted via an extremely simple and low-cost bus, together with the power (24Vdc)
required to supply these same sensors and actuators. Another important feature is that data is
transmitted cyclically, in an extremely efficient and fast manner.

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At the field level, distributed peripherals such as I/O modules, transducers,

drives, valves and operator panels communicate with automation systems via an
efficient real-time communication system, PROFIBUS DP or PA. Process data is
transmitted cyclically, while alarms, parameters and diagnostics are transmitted
acyclically, only when necessary.

At the cell level, programmable controllers such as PLCs and PCs communicate
with each other, which requires large data packets and a large number of powerful
communication functions. In addition, efficient integration into existing corporate
communication systems such as Intranet, Internet and Ethernet is an absolute
requirement, which PROFIBUS FMS and PROFINet can fulfill.

PROFIBUS-DP (“DECENTRALIZED PERIPHERY”

PERIPHERY”)

Optimized for high-speed and low-cost connectivity, this PROFIBUS version is

specially designed for communication between automation control systems and
distributed I/O at device level, and uses RS485 transmission technology, one of the
versions of the DP communication protocol and one or more typical application
profile(s) for manufacturing automation, such as Identity Systems or Robots/Controllers
(NC). PROFIBUS-DP is now available in three functionally balanced versions, DP-V0, DP-V1 and DP-V2.

PROFIBUS-PA (“PROCESS AUTOMATION”)

PROFIBUS-PA is specially designed for process automation. It allows

sensors and actuators can be connected to a common regular bus line in
intrinsically safe areas. PROFIBUS-PA enables data and power communication over
the bus using typically MBP-IS transmission technology (2-wire according to
International Standard IEC 61158-2), the communications protocol version DP-V1 and
the application profile PA Devices

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BASIC FEATURES
PROFIBUS specifies the technical and functional characteristics of an industrial
communication system, to which digital controllers can be connected at the field level or at
the cell level. PROFIBUS is distinguished into device types: master devices and
slave devices.

Master devices determine data communication on the bus. A master can send
messages without an external request when it has the bus access rights (the “token”).
Masters are also called active stations in the PROFIBUS protocol.

Slave devices are peripheral devices. Typical slave devices include I/O modules,
valves, drivers, and variable transmitters. They do not have access rights to the bus and can
only acknowledge incoming messages or send messages to the master when the master
requests them. Slaves are also called passive stations. Since they only require a small portion
of the protocol, their implementation is particularly economical.

APPLICATION PROFILE
The Application profile describes the interaction of the communication protocol with the medium.
transmission being used, in addition to defining the behavior of the device during
communication. The most important PROFIBUS application profile is currently the PA profile,
which defines the parameters and function blocks for process automation devices such as
transmitters, valves and positioners.

There are also some other profiles available, such as: ProfiSafe, Drives, Human
Machine Interface and Encoders, etc. which define the communication and behavior of
these devices in a manufacturer-independent manner.

Currently, 90% of applications involving Profibus slaves use PROFIBUS DP.

This variant is available in three versions: DP-V0 (1993), DP-V1 (1997) and DP-V2 (2002). The
origin of each version occurred according to technological advances and the demand of
applications required over time.

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Figure 101.

PROTOCOL ARCHITECTURE

PROFIBUS is based on internationally recognized standards. The architecture of

The protocol is oriented to the OSI (Open System Interconnection) reference
model according to the international standard ISO 7498. In this model, Layer 1 (physical
layer) defines the physical transmission characteristics, Layer 2 (data link layer)
defines the medium access protocol and Layer 7 (application layer) defines the
application functions. The architecture of the PROFIBUS protocol is shown in the figure.

Figure 102. PROFIBUS protocol architecture

PROFIBUS-DP uses layers 1, 2 and the user interface. Layers 3 to 7 are not defined.
This simplified architecture ensures efficient and fast data transmission. The Direct
Data Link Mapper (DDLM) provides easy access to the user interface.

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Layer 2. RS 485 transmission technology or fiber optic are available for transmission.

Figure 103.

PROFIBUS-PA uses the extended PROFIBUS-DP protocol for data transmission.

data. The transmission technology, according to IEC 61158-2, enables intrinsic safety and also allows
field devices to be powered by the bus. PROFIBUS-PA devices can easily be integrated into PROFIBUS-
DP networks using a segment coupler.

From the user's point of view, PROFIBUS presents itself in the form of a different typical application,
which has proven itself as a result of frequent applications. Each main emphasis results from a typical (but
not specifically defined) combination of modular elements from the groups "transmission
technology", "communication protocols" and "application profiles". The following examples explain this
principle, using the most well-known PROFIBUS versions.

Figure 104. PROFIBUS application-oriented features

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PROFIBUS DP is ideal for manufacturing automation; it uses RS485 transmission

technology, one of the versions of the DP communication protocol and one or more typical
manufacturing automation application profile(s), such as Identity Systems or
Robots/(NC)

PROFIBUS PA is ideal for process automation, typically with technology

MBP-IS transmission, the communications protocol version DP-V1 and the PA Devices application
profile.

Motion Control with PROFIBUS is ideal for steering control technology using RS485
transmission technology, the communication protocol version DP-V2 and the PROFIdrive
application profile.

PROFIsafe is ideal for safety-relevant applications (universal use for almost

all industries), using RS485 transmission technology or MPB-IS DP versions , one of the
available for communication and PROFIsafe application profile.

TRANSMISSION TECHNOLOGY

The application area of a fieldbus system is largely determined by the

choice of transmission technology. General requirement factors (transmission reliability,
distance to be covered or high transmission speed) are of particular importance. When
process automation applications are involved, data and power must also be transmitted over a
common cable. Since it is impossible to satisfy all requirements with a single transmission
technology, PROFIBUS offers three variants:

RS 485 TRANSMISSION TO DP

RS 485 transmission is the most frequently used transmission technology by

PROFIBUS. This transmission technology is often referred to as H2. Its application includes
all areas in which high transmission speeds with low-cost and simple installation are required.
Shielded copper twisted pair is used.

The RS 485 transmission technology is very easy to handle. Installation of the twisted pair
does not require any special knowledge. The bus structure allows addition and removal of stations
without influencing other stations. Further future expansions have no effect on stations that are
already in operation.

Transmission speeds between 9.6 kbit/sec and 12 Mbit/sec can be selected. A

common transmission speed is selected for all devices on the bus when the system is booted.

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Table 12. Basic characteristics of RS 485 transmission technology

TOPOLOGY Linear bus, active bus termination at both ends. Trunks are only allowed for baud
rates <= 1.5 Mbit/s

MEDIA Shielded twisted pair cable. Shield may be omitted depending on

ambient electromagnetic conditions (EMC).
NUMBER OF STATIONS 32 stations in each segment without repeaters, up to 127 stations with
repeaters
CONNECTORS Preferably DB-9 for IP20.
M12, Han-Brid or Hybrid type for IP65/67

All devices are connected in a bus structure (i.e., line). Up to 32 stations (masters or slaves) can be
connected on a segment. The bus is terminated by an active bus terminator at the beginning and end of
each segment (see Figure 4). To ensure error-free operation, both ends of the bus must always be
energized. Many manufacturers have designed a switched bus termination into their devices or
connectors. When more than 32 stations are used, repeaters (line amplifiers) must be used to connect the
individual bus segments.

The maximum cable length depends on the transmission speed. The

specified cable length can be increased by using repeaters. The use of more than 3
repeaters in series is not recommended.

Cable length specifications are based on Type-A cable with the following
parameters:

• Impedance: 135 to 165 Ohms

• Capacity: < 30 pf/m

• Loop resistance: 110 Ohms/km

• Wire gauge: 0.64mm

• Conductor area: > 0.34mm²

Table 13. Distances based on transmission speed for Type-A cable

Baud rate (Kbit/s) 9.6 19.2 93.75 187.5 500 1500 12000
Distance/segment 1200m 1200m 1200m 1000m 400m 200m 100m

The use of a DB-9 connector is the most common in the PROFIBUS network. The designation of the
connector pins and their connection are shown in Figure.

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Figure 105. PROFIBUS-DP connection and termination

RS485-IS

There was great demand among users to support the use of RS485 with its fast
transmission rates in intrinsically safe areas. The PNO has addressed this task and
developed a guideline for the configuration of intrinsically safe RS485 solutions with simple
device data exchange capability.

The specification of the interface details, the levels for current and voltage that
need to be adhered to for all stations must ensure safe operation during operation. An
electrical circuit allows maximum currents at a specific voltage level.

When connecting active sources, the sum of the currents of all stations cannot
exceed the maximum permissible current. An innovation of the RS485–IS concept is that,
in contrast to the FISCO model which has only one intrinsically safe source, all stations now
represent active sources. The ongoing investigations of the testing agency lead us to expect
that it will be possible to connect up to 32 stations to the intrinsically safe bus circuit.

IEC 61158-2 TRANSMISSION TO PA

The transmission technology according to IEC 61158-2 meets the requirements

of the chemical and petrochemical industries. It allows intrinsic safety and the field devices
to be powered by the bus. This technology is a bit-synchronized protocol with continuous
current transmission. It is often referred to as H1. The transmission is based on the
following principles:

• Each segment has only one power supply.

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• No power is supplied to the bus when a station is sending.

• Each field device draws a constant base current when in operation.

state of rest.

• Field devices act as passive current consumers (sink).

• Passive line termination is performed at both ends of the main line.

bus.

• Linear, tree and star networks are allowed.

To increase reliability, redundant bus segments can be designed.

For modulation it is assumed that a base current of at least 10 mA is

required by each bus station. The communication signals are generated by the
sending device by modulating +/- 9 mA on the base current.

Typically located in the control room are the process control system,
operator monitoring and control devices and segment couplers
implementing the RS 485 to IEC-61158 standard link. The couplers adapt the RS
485 signals to IEC 61158-2 signals. They provide the current for remote powering of
field devices. The power supply limits the current and voltage in the IEC
61158-2 segment.

Table 14. IEC 1158-2 characteristics

Data Transmission Digital, bit synchronized, Manchester code
Transmission Rate 31.25 Kbit/s, voltage mode

Data Security Preamble, error-proof start and end limiter

Cables Shielded twisted pair
Food Via bus or external (9-32Vdc)
Explosion Protection Class Intrinsic Safety (Eex ia/ib) and
Encapsulation (Eex d/m/p/q)
Topology Line or tree, or combined.

Number of Stations Up to 32 stations per segment, maximum 126

Maximum Distance without 1900m (Type A cable)

repeater
Repeaters Up to 4 repeaters

The process control system is normally located in the control room,

as well as monitoring and operating devices interconnected via the RS485
standard. In the field, couplers or links adapt the signals of the RS485 segment to the
signals of the IEC 61158-2 segment. They also provide the current for remote power
supply of the field devices. The power supply limits the current and voltage in the
IEC 61158-2 segment.
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Segment couplers are signal converters that adapt RS-485 signals to the IEC
61158-2 signal level. From a protocol point of view, couplers are transparent. If segment
couplers are used, the RS-485 segment speed will be limited to a maximum of 45.45 Kbit/s
or 93.75 Kbit/s, or up to 12 Mbit/s with high-speed couplers.

Links, in turn, have their own intrinsic intelligence. They make all
devices connected to the IEC 61158-2 segment into a single slave device on the RS-485
segment. In this case there is no speed limitation on the RS-485 segment which means
that it is possible to implement fast networks, for example for control functions,
including field devices connected to IEC 61158-2. In addition, they increase the
addressing capacity.

In the PROFIBUS-PA network, both tree and line structures or a combination of both
are possible. The combination generally optimizes the bus length and allows the adaptation
of an existing system.

Figure 106. Typical configuration in process automation

When the tree structure is used, all field devices connected to the fieldbus are connected
in parallel at the field distributor.

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Table 15. Cable specification for IEC 61158-2

CABLE Shielded twisted pair
DRIVER AREA 0.8 mm2 (AWG 18)
LOOP RESISTANCE 44 ohms/Km
IMPEDANCE AT 31.25 KHz 100 ohms +/-20%

ATTENUATION AT 39 3 dB/Km
KHz ASYMMETRICAL CAPACITANCE 2 nF/Km

A combination of tree and line structures optimizes bus length and

allow adaptation of the existing system.

Both ends of the main bus cable are equipped with a passive line terminator consisting
of an RC element in series with R=100 Ohms and C=1 µF.
When a bus station is connected with its poles reversed, this has no effect on the operation of the
bus. It is recommended to equip the devices with automatic polarity recognition.

The number of stations that can be connected on a segment is limited to 32. This number
is further restricted by the type of explosion protection class on the bus.
When intrinsically safe networks are operated, both the maximum supply voltage and the
maximum supply current are specified within clearly defined limits.

Table 16. Standard power supply

AREA TYPE OF MAXIMUM POWER MAXIMUM CURRENT POWER No. TYPICAL

APPLICATION OF
STATIONS
I EEX ia/ib IIC 13.5V 110mA 1.8W 8
II EEx ib IIC 13.5V 110mA 1.8W 8
III Eex ib IIB 13.5V 250mA 4.2W 22
IV Not 24V 500mA 12W 32
intrinsically safe

This specification is based on a current consumption of 10 mA per device.

If a device consumes more than 10 mA, this reduces the number of devices to be connected.

In general, to determine the maximum line length, the current requirements are
calculated, a power supply unit is selected as per Table 5, and the line length for the
selected cable type is determined as per Table 6.

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Table 17. Line Lengths for IEC 1158-2

Type I Type II Type III Type IV Type IV Type IV
Voltage V 13.5 13.5 13.5 24 24 24

Sum of currents mA ÿ110 ÿ110 ÿ250 ÿ110 ÿ250 ÿ500

necessary

Line length m ÿ900 ÿ900 ÿ400 ÿ1900 ÿ1300 ÿ650

for 0.8 mm2
Line length m ÿ1000 ÿ1500 ÿ500 ÿ1900 ÿ1900 ÿ1900
for 1.5 mm2

The connection of bus-powered devices and externally powered devices on an intrinsically

safe bus is permitted if the externally powered devices are equipped with appropriate insulation in
accordance with EN 50 020.

TRANSMISSION MEDIUM WITH OPTIC FIBER

Optical fiber can be used by PROFIBUS for applications in environments with high
electromagnetic interference or even with the aim of increasing the maximum length at high
transmission rates. Several types of fiber are available, with different characteristics, such as maximum
distance, price and application. For a quick description, see table.

PROFIBUS segments that use fiber are typically star or ring.

Some fiber optic component manufacturers allow the use of redundant links with alternative physical
media, whose transfer is automatic when a failure occurs.

Table 18.

Fiber Type Properties

“Multimode” fiberglass Medium distance, 2 to 3 km

Single-mode fiberglass Long distance, >15 km

Synthetic fiber Long distance, > 80 km

PCS/HCS Fiber Short distance, > 500m

Several manufacturers offer special connectors with integrated signal converter

RS 485 to fiber optic and vice versa. This provides a very simple method of switching between RS 485
and fiber optic transmission within a system.

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PROFIBUS BUS ACCESS PROTOCOL

All three PROFIBUS versions (DP, FMS and PA) use a uniform bus access protocol. This protocol
is implemented by layer 2 of the OSI reference model. It also includes data security and the handling
of transmission protocols.
and messages.

In PROFIBUS, layer 2 is called Fieldbus Data Link (FDL). The Media Access Control (MAC) specifies
the procedure when a station is allowed to transmit data. The MAC must ensure that only one station is
allowed to transmit data at a time. The PROFIBUS protocol was designed with two primary
requirements for Media Access Control in mind:

• During communication between complex automation systems (masters), it must be

ensuring that each of these stations has sufficient time to perform its communication tasks within a
precisely defined time interval.

• Real-time cyclic data transmission shall be implemented as quickly and simply as possible for
communication between a complex programmable controller and its designated simple I/O devices
(slaves).

Therefore, the PROFIBUS bus access protocol (Figure 7) includes the procedure of
“Token” passing which is used by complex network stations (masters) to communicate with
each other, and the master-slave procedure which is used by complex network stations to
communicate with simple I/O devices (slaves).

Figure 107. PROFIBUS configuration with 3 active stations (masters) and 7 passive stations (slaves).
The 3 masters form a logical token ring

The “Token” passing procedure ensures that the right of access to the
bus (the “Token”) is assigned to each master within a frame

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precisely defined time. The “Token” message, a special telegram for passing on access rights from
one master to the next master, must be distributed in the logical “Token” ring once to all masters within
a prescribed maximum “Token” rotation time. In PROFIBUS the “Token” passing procedure is only
used for communication between complex stations (masters).

The master-slave procedure allows the master (the active station) that is currently
has the “Token” to access the designated slaves (the passive stations). The master can send messages
to the slaves or read messages from the slaves. With this access method it is possible to implement
the following system configurations:

• Pure master-slave system

• Pure master-master system (with “Token” passing)

• A combination of both

The Figure shows a PROFIBUS configuration with three active stations (masters) and
seven passive stations (slaves). The three masters form a logical “Token” ring.
When an active station receives the “Token” telegram, it can perform its master role for a certain period of
time. During this time it can communicate with all slave stations in a master-slave communication
relationship and with all master stations in a master-master communication relationship.

A “Token” ring is the organizational chain of active stations that forms a

logical ring based on their station addresses. In this ring the “Token” (network access right) is
passed from one master to the next in a specified order (increasing addresses).

In the system start-up phase, the task of the access control (MAC) of the active stations is to
capture this logical assignment and establish the token ring. In the operational phase, defective or non-
operational stations (active stations) must be removed from the ring and new active stations can be added
to the ring. Furthermore, the access control ensures that the token is passed from one master to the
next in ascending address order. The time that the token is held by a master depends on the configured
token rotation time. Furthermore, the detection of defects in the transmission line and at the receiver
as well as the detection of errors in addressed stations (e.g. duplicate addresses) or in token
passing (e.g. multiple tokens or loss of token) are features of the access control to the PROFIBUS medium.

Another important layer 2 task is data security. Layer 2 of the

PROFIBUS formats frames that ensure high data integrity. All telegrams have Hamming Distance HD=4.
This is achieved by using special start/end delimiters and a parity bit for each octet as defined in IEC
International Standard 870-5-1.

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PROFIBUS layer 2 operates in a “connectionless” mode. In addition to transmission

point-to-point data, provides multi-point communication (Broadcast and Multicast).

Broadcast communication means that an active station sends a message without

confirmation to all other stations (masters and slaves).

Multicast communication means that an active station sends a message without

confirmation to a group of predetermined stations (masters and slaves).

Table 19. PROFIBUS data security layer services (layer 2)

SERVICE FUNCTION DP SHOVEL

SDA Send Data with Acknowledge

SRD Send and Request Data with replay • •

SDN Send Data with No acknowledge • •

CSRD Cyclic Send and Request Data with replay

In PROFIBUS-FMS, DP and PA an individual subset of the layer-2 services is

used. See Table 7. The services are called via layer-2 service access points (SAPs) by
the higher layers. In PROFIBUS-FMS these service access points are used to address
logical communication relationships. In PROFIBUS-DP and PA a precisely defined
function is assigned to each service access point. Several service access points
can be used simultaneously for all active passive stations. A distinction is made between
source (SSAP) and destination service access points (DSAP).

PROFIBUS-DP COMMUNICATION PROFILE

PROFIBUS-DP is designed for high-speed data communication at the device level. Here, central
controllers (e.g. PLCs/PCs) communicate with their distributed field devices (I/O, drives, valves, etc.) via a
high-speed serial link.

Most data communication with these distributed devices is done in a cyclic

manner. The functions required for this communication are specified by the PROFIBUS-
DP basic functions according to EN 50 170. In addition to the execution of these
cyclic functions, non-cyclic communication functions are available for intelligent
field devices allowing configuration, diagnostics and alarm handling.
These new non-cyclic functions are defined in the PROFIBUS directive No. 2.042
and are described in more detail below in the Extended DP Functions chapter.

The central controller (masters) cyclically reads input information from the slaves
and cyclically writes output information to the slaves. The bus cycle time must be shorter
than the program cycle time of the central PLC which for many applications is

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approximately 10 ms. In addition to cyclic user data transmission, PROFIBUS-DP

provides powerful functions for diagnostics and configuration. Data communication
is controlled by monitoring functions on both the master and slave. The table
provides an overview of the basic functions of PROFIBUS-DP.

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Table 20. Basic functions of PROFIBUS-DP

Transmission technology
RS-485, twisted pair, two-wire cable or fiber optic
Baud rate from 9.6 kbit/sec to 12 Mbit/sec

Bus Access

Procedure for passing “Token” between masters and master-slave procedure for slaves
Possible single-master or multi-master systems

Master and slave devices, maximum 126 stations on one communication bus

Communication
Peer-to-peer (user data transmission) or Multicast (control commands)
Cyclic master-slave user data transmission and non-cyclic master-master data transmission

Operating Modes
Operate: Cyclic transmission of input and output data

Clear: Inputs are read, and outputs are retained in a fail-safe state.

Stop: Data transmission is only possible in master-master mode

Synchronization
Control commands allow synchronization of inputs and outputs

Sync mode: Outputs are synchronized

Freeze mode: Inputs are synchronized.

Functionality

Cyclic user data transmission between DP master and DP slave(s)

Dynamic activation or deactivation of slaves individually

DP slave configuration check

Powerful diagnostic functions, 3 hierarchical levels of diagnostic messages

Synchronization of inputs and/or outputs

Address assignment for DP slaves over the bus

DP master configuration (DPM1) on the bus

Maximum 246 bytes of input and output per DP slave

Security and protection functions

All messages are transmitted with Hamming distance HD=4

Watchdog timer on DP slave

Access protection for I/O of DP slaves

Monitoring data transmission with a timer configurable by the Master

Device types
Class-2 DP master (DPM2): programming/configuration/diagnostics of DP devices Class-1 DP master

(DPM1): central programmable controller such as PLCs, PCs, etc.

DP slave: device with binary or analog I/O, drivers, valves, etc.

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BASIC FEATURES

High data transfer rate alone is not the sole criterion for success.
a data communication system. Simple installation and service, good diagnostic capability and error-
free transmission technology are also important to the user. PROFIBUS-DP represents the optimum
combination of these features.

SPEED

PROFIBUS-DP requires approximately 1 ms at 12 Mbit/sec for data transmission.

512 bits of input data and 512 bits of output data distributed across 32 stations.
Figure 7 shows the typical transmission time of PROFIBUS-DP depending on the number of stations and
the transmission speed. The significant speed increase compared to PROFIBUS-FMS results
mainly from the use of the Layer 2 SRD (Send and Receive Data) service for transmitting input/
output data in a single message cycle.

Figure 108. Cycle time of a single-master PROFIBUS-DP system

The test conditions in the figure were: Each slave with 2 input bytes and 2 output bytes
data output. The minimum slave time interval is 200 ms. TSDI = 37 bit times and TSDR = 11 bit times

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DIAGNOSTIC FUNCTIONS

The various diagnostic functions of PROFIBUS-DP enable rapid fault location. Diagnostic messages
are transmitted over the bus and collected in the master. These messages are divided into three levels:

• Station-related diagnostics

These messages concern the general operational status of the entire device (for example: high
temperature or low voltage).

• Module-related diagnostics

These messages indicate that a fault exists in a specific I/O (e.g. 8-bit output module) of a station.

• Channel-related diagnostics

These messages indicate an error in an I/O bit (e.g. short circuit on output 7).

SYSTEM CONFIGURATION AND DEVICE TYPES

PROFIBUS-DP allows single-master or multi-master systems. This provides a high degree of

flexibility during system configuration. Up to 126 devices (masters or slaves) can be connected to a bus.
The system configuration description consists of the number of stations, the assignment between the
station address and the I/O addresses, the format of the I/O data, the format of the diagnostic messages
and the bus parameters used. Each PROFIBUS-DP system can contain three different device types:

• DP Master-Class 1 (DPM1): Class-1 DP MASTER is a central controller that

exchanges information with decentralized stations (e.g. DP slaves) within a specified message
cycle. Typical master devices include programmable controllers (PLCs) and PC or VME systems.

• DP Master-Class 2 (DPM2): Class-2 DP MASTERs are programmers, devices

of settings or operator panels. They are used during commissioning for configuring the DP system or
for operation and control.

• DP SLAVE: A DP SLAVE is a peripheral device (I/O devices, drivers, HMI, valves, etc.) that collects input
information and sends output information to the controller.

The amount of I/O information depends on the device type. A maximum of 246 bytes of input and 246
bytes of output are allowed.

In mono-master systems only one master is active on the bus during the phase
network operation. Figure 8 shows the configuration of a single-master system. The PLC is

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the central controller. The distributed DP-slaves are connected to the PLC via bus.
Mono-master systems have very short cycle times.

Figure 109. PROFIBUS-DP Mono-master System

In multi-master configurations, several masters are connected to a bus. These masters are either
independent subsystems each consisting of a DPM1 master and its designated DP slaves, or additional
configuration and diagnostic devices (see Figure). The input and output images of the DP slaves can be
read by all DP masters.

However, only one DP master (e.g., the DPM1 designated during configuration)
can write to an output. Multi-master systems have a longer cycle time than single-
master systems.

Figure 110. PROFIBUS-DP multi-master system

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SYSTEM BEHAVIOR

System behavior is primarily determined by the operating state

of DPM1. DPM1 can be controlled locally or via the bus by the configuration device. There are
three main states:

STOP: In this state, no data transmission between DPM1 and DP slaves

occurs.

CLEAR: In this state, the DPM1 reads input information from the DP slaves and retains the
outputs in the safe state.

OPERATE: In this state, the DPM1 is in the data transfer phase. In a cyclic data communication,
inputs from the DP slaves are read, and output information is written to the DP slaves.

The DPM1 cyclically sends its local state to all DP slaves assigned to it with a Multicast command at a
configurable time interval.

The system reaction to an error during the DPM1 data transfer phase (for
e.g. failure of a DP slave) is determined by the “auto-clear” configuration parameter.
If this parameter is set, the DPM1 switches the outputs of all designated DP slaves to the fail-safe state
since the DP slave is no longer ready for user data transmission. The DPM1 then switches to the CLEAR
state. If this parameter is not set, the DPM1 remains in the OPERATE state whenever a fault occurs, and the
user specifies the system reaction.

CYCLIC DATA TRANSMISSION BETWEEN DPM1 AND DP SLAVES

Data transmission between DPM1 and the DP slaves assigned to it is performed automatically by
DPM1 in a defined, repeating order. When configuring the system, the user specifies the assignment of a
DP slave to DPM1 and which DP slaves will be included or excluded from the user's cyclic data transmission.

Data transmission between DPM1 and DP slaves is divided into three phases:

• Parameterization •

Configuration
• Data transfer

During the configuration and parameterization phases, each DP-SLAVE compares its
actual configuration and the expected configuration that has been configured in DPM1.
Only if the actual and desired values match will the DP-SLAVE be included in the user data transfer phase.
Therefore, device type, format and length information as well as the number of inputs and outputs must
correspond to the actual configuration. These tests provide the user with reliable protection
against parameterization errors. In addition to the transfer of user data, a transfer is performed

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automatically by DPM1, new parameterization data can be sent to the DP slaves at the user's request.

Figure 111. User data transmission in PROFIBUS-DP

SYNC AND FREEZE MODE

In addition to the transfer of user data to related stations that is performed automatically by
DPM1, the master can send control commands to a single slave, to a group of slaves or to all slaves
simultaneously. These control commands are transmitted as “Multicast” commands. They allow the
use of
modes: “sync” and “freeze” for synchronizing DP slaves.

Slaves start in “sync” mode when they receive a “sync” command from their master. The outputs
of all addressed slaves are frozen in their current states.
During subsequent user data transmissions, the output data is stored on the slaves, but the
output states remain unchanged. The stored output data is not sent to the outputs until the next “sync”
command is received. Sync mode is terminated with the “unsync” command.

Similarly, a freeze control command forces the addressed slaves to enter freeze mode . In this mode of
operation, the input states are frozen at their current value. The input data is not updated again until the
master issues the next freeze command. Freeze mode is terminated with the unfreeze command.

PROTECTION MECHANISMS

Safety and reliability are required to provide PROFIBUS-DP with efficient protection functions
against parameterization errors or transmission device errors. Time monitoring is provided for the DP
master and DP slaves. The time interval is specified during configuration.

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On the DP-MASTER: The DPM1 monitors data transmission from the slaves with the
Data_Control_Timer. A separate control timer is used for each slave. This timer expires when correct data
transmission does not occur within the monitoring interval. The user is informed when this
happens. If the automatic error reaction (Auto_Clear = True) has been enabled, the DPM1 exits the
“OPERATE” state, switches the outputs of all addressed slaves to the “fail-safe” state and changes their
“CLEAR” state.

On the DP slave: The slave uses watchdog control to detect master failures
or on the transmission line. If no communication with the master occurs within the watchdog control
interval, the slave automatically switches its outputs to the “fail-safe” state.

Furthermore, access protection is required for the inputs and outputs of DP slaves operating in multi-
master systems. This ensures that the access rights can only be exercised by the authorized master. For
all other masters, the slaves provide an image of their inputs and outputs that can be read by any master
without access rights.

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PROFIBUS-PA

PROFIBUS-PA is the PROFIBUS solution for process automation. PROFIBUS-PA connects

automation systems and process control systems with field devices such as pressure, temperature and
level transmitters. PROFIBUS-PA can be used as a replacement for 4 to 20 mA technology. PROFIBUS-PA
achieves cost savings of around 40% in planning, cabling, start-up and maintenance and offers a
significant increase in functionality and safety.

A separate power line (a power supply for potentially explosive areas may be necessary)
is required for each device in a conventional configuration. In contrast, when PROFIBUS-PA is used, only
one pair of wires is needed to transmit all information and power to the field devices. This not only saves
wiring costs but also reduces the number of I/O modules in the process control system. Isolators and
barriers are no longer necessary since the bus is supplied with intrinsically safe sources. PROFIBUS-
PA allows measurement, control and regulation via a simple two-wire line.

It also allows powering field devices in intrinsically safe areas. PROFIBUS-PA allows maintenance
and connection/disconnection of devices during operation without affecting other stations in
potentially explosive areas.

Figure 112. Profibus Network - DP and Profibus - PA

The use of PROFIBUS in process automation and control can achieve savings of up to 40% in
planning, wiring, commissioning and maintenance, as well as offering a significant increase in system
functionality and safety. The following figure shows the differences between the connections of a
conventional system (4 to 20 mA) and a system based on PROFIBUS.

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Figure 113. Comparison between conventional and PROFIBUS connections

The Profibus - PA network has the following characteristics:

It is a communication protocol dedicated to process automation and optimized for field

equipment such as transmitters, valve positioners, actuators, converters, etc.

• The physical layer complies with IEC 1158-2 standard, variant H1.
• Baud rate: 31.25 kbit/s;
• Communication signal in Manchester coding, with current modulation. • Topology: Bus,
tree/star, point to point. • Power supply: via bus or external,
9-32Vdc in non-intrinsically safe areas. • Allows a maximum of 32 devices (non-”Ex”) per segment,
for a total of 126
equipment.
• Possibility of use in classified areas (Intrinsically Safe). • Approximately 9 devices
(Explosion Group IIC). • Approximately 23 devices (Explosion
Group IIB). • Field devices are interconnected and powered via
fieldbus. There is also the possibility of external power supply, depending on the type of device and

manufacturer;

• Each field device has a physical address that is unique on the bus. • Maximum cabling of
1900m, without repeaters. • Allows 4 repeaters: distances
up to 10Km. • Spur max of 120m / spur.

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PROFIBUS DP and PA uses access methods according to the variant of

protocol, and we have:

• Token - Pass (Passing the baton) – For example master to master, between PLCs. • Master - Slave (Master

- Slave) – For example between configuration software and

transmitters in the field

• Mixed – For example between PLCs and transmitters in the field.

PROFIBUS DP AND PA NETWORK ELEMENTS

Basically, we can mention the following elements of a Profibus network:

MASTERS

These are elements responsible for controlling the bus. They can be of two classes:

• Class 1: responsible for cyclic operations (reading/writing) and mesh control

open and closed of the control/automation system (PLC).

• Class 2: responsible for acyclic access to the parameters and functions of PA equipment
(engineering station or operating station: Simatic PDM).

Note: - the masters work with the physical medium RS485 or fiber optics (up to 12 Mbits/s when
using link devices (IM157-Siemens) or SK2 (P+F high-speed coupler) the field equipment is only slave.

Figure 114. Class 1 master PLC

COUPLERS

These are devices used to translate the physical characteristics between PROFIBUS DP and
PROFIBUS PA (H1: 31.25 kbits/s). And also:

They are transparent to the masters (they do not have a physical address on the bus);

They meet safe (Ex) and (Non-Ex) applications, defining and limiting the maximum number of
devices in each PA segment. The maximum number of devices in
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a segment depends, among other factors, on the sum of quiescent currents and equipment failures (FDE)
and distances involved in the cabling.

They can be powered up to 24 Vdc, depending on the manufacturer and the area of operation.
classification.

They can work with the following communication rates, depending on the manufacturer: P+F (93.75
kbits/s and SK2: 12Mbits/s) and Siemens (45.45 kbits/s).

Figure 115. Siemens and Pepperl + Fuchs coupler

Figure 116. Table with technical information about couplers

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Figure 117. Basic Architecture with Couplers

LINKS DEVICES

These are devices used as slaves on the PROFIBUS DP network and masters on the PROFIBUS PA
network (H1: 31.25kbits/s). They are used to achieve high speeds of up to 12Mbits/s on the DP bus. And
also:

• They have a physical address on the bus;

• Allows up to 5 couplers to be coupled, but limits the number of devices

30 on a “Non-Ex” bus and 10 on an “Ex” bus.

Figure 118. Siemens Link Device

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Figure 119. Basic Architecture with Couplers and Links

TERMINATORS

It consists of a 1µF capacitor and a 100ÿ resistor connected in series with each other and
in parallel to the bus. It has the following functions:

Current signal shunt: the communication signal is transmitted as current but

received as voltage. The terminator makes this conversion. A signal of 750 to 1000 mV will be
present in the communication network.

Protection against reflection of the communication signal: must be placed on both

bus terminations, one at the end and one usually at the coupler.

Figure 120. Terminator

ADDRESSING IN THE PROFIBUS DP AND PA NETWORK

Regarding addressing, we can have two architectures to analyze, where

fundamentally we have the transparency of the couplers and the assignment of addresses to the link
devices, as we can see in the next figures.

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Figure 121. Addressing with Couplers

Figure 122. Addressing with Links

Note that in the figure, the addressing capacity is significantly increased with the
presence of links, since these are slaves for the DP and masters for the PA.

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OVERVIEW OF A PROFIBUS SYSTEM

Figure 123. Generic PROFIBUS system

Note in the figure the architecture of a PROFIBUS system, where we can
see the basic elements and also, a fundamental point which is the integration with equipment 4-
20mA and HART that are connected via Smar converters (IF-303 and FI-303) as well as
integration with 3-15 psi in the FP-303 converter.

PROFIBUS/PA PHYSICAL MEDIUM

It is recommended to use a 1x2, 2x2 or 1x4 twisted pair cable with shield, and also:

• Diameter: 0.32 mm2 (AWG 22); •

Impedance: 35 to 165 Ohm at frequencies from 3 to 20 MHz;
• Capacitance: less than 30 pF per meter.
In addition to this cable, we can also use one of the cables listed in the table
below, but respecting the maximum distance limits.

Table 21.
TWISTED SHIELD PAIR GAUGE LENGTH TYPE

Simple Yes Yes 0.8 mm2 (18 AWG) 1900 m THE

Multi Yes Yes 0.32 mm2 (22 AWG) 1200 m B

Multi No Yes 0.13 mm2 (26 AWG) 400 m W

Multi Yes No 1.25 mm2 (16 AWG) 200 m D

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Below we will show a table with distances based on speed.

transmission for type A cable in RS485.

Table 22.
Baud Rate 9.6 19.2 93.75 187.5 500 1500 12000
Kbits/s

Distance/ 1200 1200 1200 1000 400 200 100

segment ( m )

Below we will show the properties of optical fiber, if it is used.

Table 23.
FIBER TYPE PROPERTIES

Glass - Multimode Medium distance , 2 to 3 km

Glass - Multimode Long distance, > 15 km

Synthetic Long distance, > 80 km
PCS/HCS Short distance, < 500 m

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PROFIBUS-PA DEVICE PROFILE

The PA profile consists of a generic data sheet containing definitions applicable

to all device types and a device data sheet containing information specific to the
given device. The profile is suitable for describing both single-variable devices and
multi-variable devices.

The current PROFIBUS PA profile (version 3.0) defines the device datasheet
for the most common transmitter types:
• Pressure and Differential Pressure •

Level, Temperature and Flow •

Valves and Positioners • Analyzers

FUNCTION BLOCKS PA
The PA profile supports interchangeability and interoperability of PA field
devices from different manufacturers by using the internationally recognized model
of function blocks that describe device parameters and functions. Function blocks
represent different user functions, such as analog input or analog output.
In addition to the application-specific function blocks, two function blocks are
available for specific device characteristics (Physical Block and Transducer
Block). The input and output parameters of the function blocks can be connected via
bus and linked to process control applications.

Physical Block: contains general device information, such as:

device name, manufacturer, version and serial number.

Transducer Block: contains device-specific data, such as calibration parameters.

Analog Input Block – AI: provides the measured value

by the sensor, with status and scale.

Analog Output Block – AO: Provides the analog output value specified by the
control system.

Digital Input Block – DI: provides the control system with the digital input value.

Digital Output Block – DO: Provides digital output with the

value specified by the control system.

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An application consists of several function blocks. The function blocks are

integrated into the field devices by the device manufacturer and can be accessed via
communication as well as via the Engineering Terminal.

Device behavior is described by specifying variables

standardized depending on the particular transmitter. The figure shows the
principle of a pressure transmitter that is described with the “analog input” function block.

Figure 124. Parameter diagram of a pressure transmitter in PROFIBUS-PA

Each device will provide the parameters specified in PROFIBUS-PA.

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Table 24. AI function block parameters

READING WRITE PARAMETER FUNCTION
OUT X Current measured value of process variable

PV_SCALE X X Process variable measurement range scale, codes for units

and number of digits after the decimal point

PV_FTIME X X Response time of the output of the “function block” in

seconds

ALARM_HYS X X Alarm hysteresis, works as % of the measurement range

HI_HI_LIMIT X X High alarm threshold: If exceeded, alarm bit and status are set

HI_LIMIT X X High alarm limit: If exceeded, warning and status bits are set

LO_LIMIT X X Low alarm limit: If exceeded, warning and status bits are set

LO_LO_LIMIT X X Very low alarm threshold: If exceeded below, interrupt and status
bits are set

HI_HI_ALARM X Very high alarm threshold status

HI_ALARM X High alarm limit status

LO_ALARM X Low alarm limit status

LO_LO_ALARM X Very low alarm threshold status

“FAILSAFE” APPLICATIONS

The demand for more resources in the automation and process control sector, through
the advent of digital technology and the rapid expansion of Fieldbus, favored the development
of technology dedicated to the diagnosis and treatment of safe failures.
Mainly focused on protecting people, equipment/machines and the environment, always aiming for the
ideal safe system.

This secure system requires, in other words, that data and information can be validated in relation to
their values and the time domain, which must be applicable to the system as a whole.

This involves ensuring that the data received was sent correctly and that the sender is also the
correct transmitter. Furthermore, that this is the information expected at a given time and that the
information received is sequentially correct, etc.

Currently, the most typical example of an international security standard and one that involves
The main focus of most developers and implementers of safety-related systems is the so-called IEC
61508. This standard shows the activities involved in the entire life cycle of programmable electronic
systems in relation to safety. Therefore, it addresses both hardware and software requirements.

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The risk of accidents in industrial processes is vast and the probability of an accident occurring is
dependent on the probability of system failure. The implication of failures depends on the type and safety
requirements of the application.

The PROFIBUS application profile “PROFIsafe” - Profile for Safe Technology describes
mechanisms for safe communication between fail-safe peripherals and safe controllers. It is based on
the requirements of standards and directives for safety-oriented applications, such as IEC 61508 and
EN954-1, as well as on the experience of equipment manufacturers with Fail-Safe and the PLC
manufacturer community.

This profile supports safe applications in a wide range of field applications.

And, instead of using special buses for safety functions, it allows the implementation of safe
automation through an open solution and in the PROFIBUS standard, guaranteeing effective
cabling costs, system consistency in relation to parameterization and remote diagnostic functions.

Ensures security in decentralized control systems through Fail-Safe communication

and device and equipment security mechanisms.

Below are some examples of areas of application for this security profile:

• Manufacturing Industry.

• Rapid protection of people, machines and the environment.

• Emergency stop functions.

• Light barriers.

• Input control.

• Scanners.

• Drivers with integrated security.

• General process control. • Chemical

and petrochemical areas.

• Public transport.

• Others.

PROFIBUS open technology meets a wide range of requirements,

applications in terms of safety according to PROFIsafe:

• Independence between relevantly secure communication and secure communication.

• Applicable to SIL3 (IEC61508), AK6 (DIN V 19250) and control category 4 (KAT4) (EN 954-1)
levels.

• Redundancy is used only to increase reliability.

• Any master or DP link can be used.

• In the implementation, DP masters, ASICs, links and couplers should not be modified,
as long as the security functions are implemented above OSI layer 7 (i.e., no changes or accommodations
in the DP protocol).
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• The implementation of secure transmission functions must be restricted to communication

between devices and must not restrict their number.

• It is always a 1:1 communication relationship between F devices.

• Transmission times must be monitored.

Figure 125. In the ProfiSafe profile, failsafe devices can communicate via PROFIBUS
In practice, secure applications and standards will share communication systems
PROFIBUS DP simultaneously. The safe transmission functions include all measures that can be
deterministically detected in the event of potentially dangerous faults.
These can be added to the standard transmission system with the intention of minimizing its effects.
These include, for example, random malfunction functions, EMI effects, systematic hardware or
software failures, etc.

For example, it is possible that during a communication part of a frame is lost, or that part of it appears repeated,
or that it appears in the wrong order or even late.

At PROFIsafe, some preventive measures are taken with the aim of surrounding the
possible causes of failures and, when they occur, that they happen with
security:

• Consecutive numbering of all secure messages: here the aim is to minimize loss of
communication, insertion of bytes in the frame and incorrect sequence.

• Watchdog timer system for messages and their acknowledgements:

controlling delays.

• A password between sender and receiver: avoiding linking between standard and secure
messages.

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• Additional telegram protection with the inclusion of 2 to 4 bytes of CRC: preventing

corruption of user data and linking between standard and secure messages.

These measures must be analyzed and taken in a Fail-Safe data unit.

PROFIsafe is a single-channel software solution that is implemented as

an additional layer above layer 7 in devices. A secure layer defines methods to increase the probability
of detecting errors that may occur between two devices/equipment communicating on a fieldbus.

The big advantage is that it can be implemented without changes, providing

protection of users' investments.

Cyclic communication mechanisms are used in physical media 485 or H1 (31.25kbits/s).

Acyclic communication is used for irrelevant levels of data security. It guarantees very short response
times, ideal for manufacturing and intrinsically safe operation, according to the requirements of
the process control area.

Through an intelligent selection and combination of available measures, such as

consecutive numbering, time monitoring with recognition, source-target identification and CRC control,
as well as the patented SIL Monitor, it was possible to achieve the desired failure probability class up to SIL3
or AK6, or category 4. For manufacturers of Failsafe devices, there is special software that implements
all definitions of the PROFISafe profile. A relevant factor are the positive reports that the PROFISafe
profile has received from the TÜV and BIA institutes.

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STANDARD: AS-I

The AS-i network or Actuator/Sensor Interface is a subnetwork for lower-level automation systems, i.e.
shop floor automation. The simplest types of sensors and actuators are connected in this network.

Figure 126.

The AS-i network has the following characteristics:

• Allows connection of binary sensors and actuators, being used both for
exchange data between sensors/actuators with the Master, as well as to power the sensors
and actuators.

• AS-i modules are available in versions from 1 to 8 bits (channels) and have an IP65 or IP67
protection rating. They are supplied for direct connection to machines or equipment.

• Slaves can be replaced without reconfiguration

• An AS-i Master module uses a maximum cyclic data transfer time of 5 ms with up to 32 slave
stations (in the AS-i V1 version) and 10 ms with up to 61 slave stations (in the AS-i V2.1 ,
version)

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The following figure shows a typical configuration of an application with an AS-i network,
composed of a master member of a control system and some slaves.

Figure 127.

The following figures show the architectures most commonly used in the application.
of a system with AS-i network:

• AS-i master integrated into a controller (normally a PLC).

Figure 128.

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• AS-i master belonging to a “gateway” interfacing another network, for

PROFIBUS example with AS-i network.

Figure 129.

Comparing an application for conveyor control in an industry

automotive, using a system of inputs and outputs called TRADITIONAL, connecting sensors and
actuators point to point to the control system and a system using an AS-i network for this purpose, all
the advantages existing in this system can be observed.

Figure 130.

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Figure 131.

AS-I NETWORK COMPONENTS

The AS-i network is composed of a MASTER module, AS-i SLAVES of the module type or
sensors with integrated AS-i chip, AS-i cable, power supply unit, AS-i programming
device and monitoring software.

Figure 132.

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AS-I MODULES

The concept of AS-i modules is defined in such a way that they are devices capable of connecting
sensors and actuators to the bus. The sensors/actuators are connected to the modules via M12 type
connectors with pinout corresponding to the DIN IEC 947 5-2 standard.

Figure 133.

The modules have dimensions of 45 x 45 x 80 mm. There are two fundamental types of modules:

ACTIVE AS-I MODULE

Active AS-i module, which already has the AS-i "chip" integrated, thus allowing the interconnection of
this module conventional sensors and actuators.

PASSIVE AS-I MODULE

Passive AS-i module, which works as a distributor and offers the ability to connect sensors and actuators
with an integrated AS-i "chip".

Figure 134.

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AS-I CABLE

The AS-i cable is rubberized with 2 wires (2x1.5 mm2) and has a profile that
does not allow connections with reversed polarity. This cable has a connection
technique through the penetration of the contacts directly into the protective rubber,
ensuring low contact resistance and high mechanical protection.

Figure 135.
For this connection, coupling modules are used between the cable and the AS-i modules.

Figure 136.

PROGRAMMING DEVICE

For programming and maintenance purposes, there is a portable type device

"Hand-held" with liquid crystal and keyboard that can be connected at any point in
the AS-i network, with the following functions:

• Monitoring Network data is stored and evaluated by a certain

time.

• AS-i Slave Simulation The device works as a Slave

AS-i "Slave" with freely selectable address.

• AS-i Master Simulation This function allows you to check the parameters of
configuration and addressing of an AS-i slave

• Slave address programming The address of an AS-i slave

can be viewed, modified and assigned.

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Figure 137.

Another device whose sole function is to address AS-i slaves is the AS-i addressing unit. With this
unit, it is possible to save AS-i addresses in the modules' EEPROM.

Figure 138.

TECHNICAL CHARACTERISTICS

The AS-i network is defined as a single-master network, meaning that there is only one master per
AS-i segment, which controls all data exchange. This master scans all slaves one after the other and waits
for a response.
In this sequential call of the slaves the master can write or read data.

The Master/Slave access method with cyclic scanning, used by the AS-i network
guarantees a determined response time of AS-i slave devices.

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Figure 139.

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SPECIFICATIONS

There are currently two product versions available in the AS-i standard:

• AS-i V1

• AS-i V2.1

The basic difference between the two versions can be compared in the
specifications shown below.

Table 25.
FEATURE V1 Tree SPECIFICATION SPECIFICATION V2.1 Tree

Topology

Physical environment Unshielded two-wire cable Unshielded two-wire cable

for data and power for data and power
typically 24 Vdc up to 8A, without typically 24 Vdc up to 8A, without
terminating resistor. terminating resistor.

Maximum cable length 100m without repeater or 300m 100m without repeater or 300m
with repeaters with repeaters

Maximum number of devices 31 62

slaves

Maximum number of participants per slave Up to 4 sensors and 4 actuators Up to 4 sensors and 4 actuators
per slave for slave “A” and 4 sensors
and 4 actuators for slave “B”

Maximum number of inputs and outputs 124 inputs and 124 outputs 248 inputs and 186 outputs

Addressing Slaves receive permanent address Slaves receive permanent address

via master or hand-held via master or hand-held

Data transfer 4 bits per slave and 4 bits per slave and
message message

Response time 5 ms with 31 slaves 10ms with 62 slaves

Error detection Incorrect messages are Incorrect messages are

detected and repeated detected and repeated

Access method Cyclic Master/Slave Cyclic Master/Slave

Real-time diagnostics of Does not allow Allows

slaves

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