Mekelle University

Ethiopian Institute of Technology – Mekelle (EiT-M)

School of Electrical and Computer Engineering

Industrial Automation

Teaching Material

Prepared by:Mahder Girmay

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 Chapter One
Introduction to Industrial Automation
• The word ‘Automation’ is derived from greek words “Auto” (self) and “Matos” (moving). Automation
therefore is the mechanism for systems that “move by itself”.

• Automation is a set of technologies that results in operation of machines and systems without
significant human intervention and achieves performance superior to manual operation.

Q:Why does an automated system achieve superior performance compared to a manual one?

• Automation Systems may include Control Systems but the reverse is not true. Control Systems may be
parts of Automation Systems.

• The main function of control systems is to ensure that outputs follow the set points. However,
Automation Systems may have much more functionality, such as computing set points for control
systems, monitoring system performance, plant startup or shutdown, job and equipment scheduling
etc.

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 Role of Automation in industry
• Manufacturing processes, basically, produce finished product from raw/unfinished material using
energy, manpower and equipment and infrastructure.

• Since an industry is essentially a “systematic economic activity”, the fundamental objective of any
industry is to make profit.

• Roughly speaking, Profit = (Price/unit – Cost/unit) x Production Volume

• So profit can be maximized by producing good quality products, which may sell at higher price, in
larger volumes with less production cost and time.

• Similarly, systems such as Automated Guided Vehicles, Industrial Robots, Automated Crane and Conveyor
Systems reduce material handling time.

• Automation also reduces cost of production significantly by efficient usage of energy, manpower and material.

• The product quality that can be achieved with automated precision machines and processes cannot be achieved
with manual operations. Moreover, since operation is automated, the same quality would be achieved for
thousands of parts with little variation.

• Industrial Products go through their life cycles, which consist of various stages.

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 Programmable Logic Controllers
Programmable logic controllers, also called programmable controllers or PLCs, are solid-state members
of the computer family, using integrated circuits instead of electromechanical devices to implement
control functions. They are capable of storing instructions, such as sequencing, timing, counting,
arithmetic, data manipulation, and communication, to control industrial machines and processes.

Fig.1 Conceptual diagram of a PLC application

Programmable controllers have many definitions. However, PLCs can be thought of in simple terms as
industrial computers with specially designed architecture in both their central units (the PLC itself) and
their interfacing circuitry to field devices (input/output connections to the real world).
PLC versus Hard-wired Control
Prior to PLCs, many of these control tasks were solved with contactor or relay controls. This is
often referred to as hard-wired control. Circuit diagrams had to be designed, electrical
components specified and installed, and wiring lists created. Electricians would then wire the
components necessary to perform a specific task. If an error was made the wires had to be
reconnected correctly. A change in function or system expansion required extensive component
changes and rewiring.

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Advantages of PLC
 Simple to install and quick modification of programs
 Small proportion of hardware for universal applications
 Easy fault finding or simple troubleshooting
 Automatic documentation
 Programming without hardware
 Extension using modules
 High reliability and processing speed
 Low space requirement and low power consumption
 No moving parts hence no wearing of parts

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 Disadvantages of a PLC
 Serial processing
 Programming unit required
 High initial cost for simple processes
 Sensitive to dust, high temperature and high Humidity
 Repair must be made by qualified personnel
 No uniform programming language

Typical areas of PLC applications

Since its inception, the PLC has been successfully applied in virtually every segment of industry,
including steel mills, paper plants, food-processing plants, chemical plants, and power plants.
PLCs perform a great variety of control tasks, from repetitive ON/OFF control of simple
machines to sophisticated manufacturing and process control.
Because the applications of programmable controllers are extensive, it is impossible to list them
all in this book. However, list below provides a small sample of how PLCs are being used in
industry.

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Basic PLC Hardware and Principles of operation
A programmable controller consists of two basic sections:
 The central processing unit
 The input/output interface system

The central processing unit (CPU) governs all PLC activities. The following three components
form the CPU:
 The processor
 The memory system
 The system power supply

The operation of a programmable controller is relatively simple. The input/output (I/O) system is
physically connected to the field devices that are encountered in the machine or that are used in
the control of a process. These field devices may be discrete or analog input/output devices, such
as limit switches, pressure transducers, push buttons, motor starters, solenoids, etc.
The I/O interfaces provide the connection between the CPU and the information providers
(inputs) and controllable devices (outputs).During its operation, the CPU completes three
processes:
(1) It reads, or accepts, the input data from the field devices via the input interfaces,
(2) It executes, or performs, the control program stored in the memory system, and

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(3) It writes, or updates, the output devices via the output interfaces.
This process of sequentially reading the inputs, executing the program in memory, and updating
the outputs is known as scanning. The input/output system forms the interface by which field
devices are connected to the controller. The main purpose of the interface is to condition the
various signals received from or sent to external field devices. Incoming signals from sensors
(e.g., push buttons, limit switches, analog sensors, selector switches, and thumbwheel switches)
are wired to terminals on the input interfaces. Devices that will be controlled, like motor starters,
solenoid valves, pilot lights, and position valves, are connected to the terminals of the output
interfaces. The system power supply provides all the voltages required for the proper operation
of the various central processing unit sections.
Although not generally considered a part of the controller, the programming device, usually a
personal computer or a manufacturer’s mini programmer unit is required to enter the control
program into memory. The programming device must be connected to the controller when
entering or monitoring the control program.

Fig. Hardware of the PLC System

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 Fig. Conceptual Operation of PLC

Fig. Typical PLC Training Module

Components of PLC Hardware

1. The Processor unit or central processing unit (CPU) is the unit containing the
microprocessor and this interprets the input signals and carries out the control actions,
according to the program stored in its memory, communicating the decisions as action
signals to the outputs.

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2. The power supply unit is needed to convert the mains a.c. voltage to the low d.c. voltage
(5 V) necessary for the processor and the circuits in the input and output interface
modules.

Fig. The power supply and logic unit

3. The programming device is used to enter the required program into the memory of the
processor. The program is developed in the device and then transferred to the memory
unit of the PLC. A programming device can also be used to monitor inputs and outputs,
with highlighted contacts indicating an ON condition.

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4. The memory unit is where the program is stored that is to be used for the control actions
to be exercised by the microprocessor and data stored from the input for processing and
for the output for outputting.

5. The input and output sections are where the processor receives information from
external devices and communicates information to external devices. The inputs might
thus be from switches, or other sensors such as photo-electric cells, temperature sensors,
or flow sensors, etc. The outputs might be to motor starter coils, solenoid valves, etc.
Input and output devices can be classified as giving signals which are discrete, digital or
analogue. Devices giving discrete or digital signals are ones where the signals are either
off or on. Thus a switch is a device giving a discrete signal, either no voltage or a voltage.
Digital devices can be considered to be essentially discrete devices which give a
sequence of on−off signals. Analogue devices give signals whose size is proportional to
the size of the variable being monitored. For example, a temperature sensor may give a
voltage proportional to the temperature.

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 Fig. Input/output Interface
Input/output Units
Input signals from sensors and the outputs required for actuating devices can be:
1. Analogue, i.e. a signal whose size is related to the size of the quantity being
sensed.
2. Discrete, i.e. essentially just an on−off signal.
3. Digital, i.e. a sequence of pulses.

Discrete input: A discrete input also referred to as a digital input, is an input that
is either in an ON or OFF condition. Pushbuttons, toggle switches, limit switches,
proximity switches, and contact closures are examples of discrete sensors which
are connected to the PLCs discrete or digital inputs. In the ON condition a discrete
input may be referred to as logic 1 or logic high. In the OFF condition a discrete
input may be referred to as logic 0 or a logic low.

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Analog inputs: An analog input is an input signal that has a continuous signal.
Typical analog inputs may vary from 0 to 20 milliamps, 4 to 20milliamps, or 0 to
10 volts. In the following example, a level transmitter monitors the level of liquid
in a tank. Depending on the level transmitter, the signal to the PLC can either
increase or decrease as the level increases or decreases.

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Analog Input Processing
Analogue signals can be inputted to a PLC if the input channel is able to convert the signal to a
digital signal using an analogue-to-digital converter.
A single analogue input signal gives rise to on−off output signals along perhaps eight separate
wires. The eight signals then constitute the so-termed digital word corresponding to the
analogue input signal level. With such an 8-bit converter there are 28 = 256 different digital
values possible; these are 0000 0000 to 1111 1111, i.e. 0 to 255. The digital output goes up in
steps and the analogue voltages required to produce each digital output are termed quantization
levels.

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The analogue voltage has to change by the difference in analogue voltage between successive
levels if the binary output is to change. The term resolution is used for the smallest change in
analogue voltage which will give rise to a change in one bit in the digital output. With an 8-bit
ADC, if, say, the full-scale analogue input signal varies between 0 and 10 V then a step of one
digital bit involves an analogue input change of 10/255 V or about 0.04 V. This means that a
change of 0.03 V in the input will produce no change in the digital output. The number of bits in
the output from an analogue-to-digital converter thus determines the resolution, and hence
accuracy, possible. If a 10-bit ADC is used then 210 = 1024 different digital values are possible
and, for the full-scale analogue input of 0 to 10 V, a step of one digital bit involves an analogue
input change of 10/1023 V or about 0.01 V. If a 12-bit ADC is used then 212 = 4096 different
digital values are possible and, for the full-scale analogue input of 0 to 10 V, a step of one digital
bit involves an analogue
input change of 10/4095 V or about 2.4 mV. In general, the resolution of an n-bit ADC is 1/(2n –
1).
The following illustrates the analogue-to-digital conversion for an 8-bit converter when the
analogue input is in the range 0 to 10 V:

To illustrate the above, consider a thermocouple used as a sensor with a PLC and
giving an output of 0.5 mV per oC. What will be the accuracy with which the PLC
will activate the output device if the thermocouple is connected to an analogue
input with a range of 0 to 10 V d.c and using a10-bit analogue-to-digital converter?
With a 10-bit converter there is210 = 1024 bits covering the 0 to 10 V range. Thus a
change of 1 bit corresponds to 10/1023 V or about 0.01 V, i.e. 10 mV. Hence the
accuracy with which the PLC recognizes the input from the thermocouple is ±5
mV or ±10oC.

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Input Sourcing and Sinking
The terms sourcing and sinking refer to the manner in which d.c. devices are interfaced with the
PLC. For a PLC input unit, with sourcing it is the source of the current supply for the input
device connected to it. With sinking, the input device provides the current to the input unit.

Basic input unit circuits for discrete and digital D.C. and discrete A.C. inputs.
Optoisolators are used to provide protection. With the a.c. input unit, a rectifier bridge network is
used to rectify the a.c. so that the resulting d.c. signal can provide the signal for use by the
optoisolator to give the input signals to the CPU of the PLC. Individual status lights are provided
for each input to indicate when the input device is providing a signal.

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Discrete Outputs: A discrete output is an output that is either in an ON or OFF
condition. Solenoids, contactor coils, and lamps are examples of actuator devices
connected to discrete outputs. Discrete outputs may also be referred to as digital
outputs. In the following example, a lamp can be turned on or off by the PLC
output it is connected to.

Analog outputs: An analog output is an output signal that has a continuous signal.
The output may be as simple as a 0-10 VDC level that drives an analog meter.
Examples of analog meter outputs are speed, weight, and temperature. The output
signal may also be used on more complex applications such as a current-to-
pneumatic transducer that controls an air-operated flow-control valve.

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Analog Output Processing
Analogue outputs are frequently required and can be provided by digital-to-
analogue converters (DACs) at the output channel. The input to the converter is a
sequence of bits with each bit along a parallel line.

A bit in the 0 line gives rise to a certain size output pulse. A bit in the 1line gives rise to an
output pulse of twice the size of the 0 line pulse. A bit in the 2 line gives rise to an output pulse
of twice the size of the 1 line pulse. A bit in the 3 line gives rise to an output pulse of twice the
size of the 2 line pulse, and so on. All the outputs add together to give the analogue version of
the digital input. When the digital input changes, the analogue output changes in a stepped
manner, the voltage changing by the voltage changes associated with each bit. For example, if

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we have an 8-bitconverter then the output is made up of voltage values of 28 = 256 analogue
steps. Suppose the output range is set to 10V d.c. One bit then gives a change of 10/255 V or
about 0.04 V.
Thus we have:

Analogue output modules are usually provided in a number of outputs, e.g. 4 to 20 mA, 0 to +5
V d.c., 0 to +10 V d.c., and the appropriate output is selected by switches on the module.
Modules generally have outputs in two forms, one for which all the outputs from that module
have a common voltage supply and one which drives outputs having their own individual voltage
supplies.
Figure 4.11 shows the basic principles of these two forms of output.

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Output Sourcing and Sinking

With a PLC output unit, when it provides the current for the output device it is said to be
sourcing and when the output device provides the current to the output unit it is said to be
sinking. Quite often, sinking input units are used for interfacing with electronic equipment and
sourcing output units for interfacing with solenoids.

Output units can be relay, transistor or triac.

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6. The communications interface is used to receive and transmit data on communication
networks from or to other remote PLCs. It is concerned with such actions as device
verification, data acquisition, synchronization between user applications and connection
management.

Fig. Communication Network

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Basics of PLC Programming
A program consists of one or more instructions that accomplish a task.
LOGIC CONCEPTS
Programmable controllers make decisions based on the results of these kinds of logical
statements.
Operations performed by digital equipment, such as programmable controllers, are based on
three fundamental logic functions—AND, OR, and NOT. These functions combine binary
variables to form statements. Each function has a rule that determines the statement outcome
(TRUE or FALSE) and a symbol that represents it. For the purpose of this discussion, the result
of a statement is called an output (Y), and the conditions of the statement are called inputs (A
and B). Both the inputs and outputs represent two-state variables, such as those discussed earlier
in this section.
THE AND FUNCTION
The AND output is TRUE (1) only if all inputs are TRUE (1).

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THE OR FUNCTION
The OR output is TRUE (1) if one or more inputs are TRUE (1).

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THE NOT FUNCTION
The NOT output is TRUE (1) if the input is FALSE (0).Conversely, if the output is FALSE (0),
the input is TRUE (1). The result of the NOT operation is always the inverse of the input;
therefore, it is sometimes called an inverter.

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The NOT function, unlike the AND and OR functions, can have only one input. It is seldom used
alone, but rather in conjunction with an AND or an OR gate.

EXAMPLE
Show the logic gate, truth table, and circuit representation for a solenoid valve (V1) that will be
open (ON) if selector switch S1 is ON and if level switch L1 is NOT ON (liquid has not reached
level).

Solution

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PLC programming languages
Basically there are three PLC programming languages, namely;
1. Ladder logic (ladder Diagram)
Ladder logic uses components that resemble elements used in a line diagram format to describe
hard-wired control.
The left vertical line of a ladder logic diagram represents the power or energized conductor. The
output element or instruction represents the neutral or return path of the circuit. The right vertical
line, which represents the return path on a hard-wired control line diagram, is omitted. Ladder
logic diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as
networks. A network may have several control elements, but only one output coil.
 The inputs a/o outputs are all identified by their addresses, the notation used depending
on the PLC manufacturer.

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2. Statement list
Statement list is a programming language using mnemonic abbreviations of Boolean
logic operations. Boolean operations work on combination of variables that are true or
false. A statement is an instruction or directive for the PLC.
3. Function Block Diagrams
Function block is represented as a box with the function name written in. Each function
has a name to designate its specific task. Functions are indicated by a rectangle. Inputs
are shown on the left-hand side of the rectangle and outputs are shown on the right-hand
side.

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Ladder Diagram to Instruction list

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Input/Output addressing
S7-200 inputs and outputs are labeled at the wiring terminations and next to the
status indicators. These alphanumeric symbols identify the I/O address to which a
device is connected. This address is used by the CPU to determine which input is
present and which output needs to be turned on or off. I designate a discrete input
and Q designates a discrete output. The first number identifies the byte; the second
number identifies the bit. Input I0.0, for example, is byte 0, bit 0.
I0.0 = Byte 0, Bit 0
I0.1 = Byte 0, Bit 1
I1.0 = Byte 1, Bit 0
I1.1 = Byte 1, Bit 1
The following table identifies the input and output designations.

The Logic designing method for PLC control program

Steps

1 Analyzing the control requirement

○
○
2 Write the logic expressions
○
3 Change it into ladder diagram
○
4 debug the program
Example 1:
The figure below shows a water tower. L1，H1，L2，H2 are sensors for water-level.
Electromagnetic valve Y control influent water motor M is responsible for drawing water.

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Requirement

○
1 when the low level L1 in tower 1 acting, Y should be open; when the high level H1 acting, Y
should be close

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2 when the high level H1 in tower 1 and the low level L2 in tower 2 acting together , M should
operate and M will stop work when the high level H2 acting.

Solution:
1. Analyzing the control requirement and Write the logic expressions

When L1 acting——L1，When L1 stopping—— L1 ;

When L2 acting——L2，When L2 stopping—— L2 ;

When H1 acting——H1, when H1 stopping—— H1 ;．

When H2 acting——H2, when H2 stopping—— H2 .

According to the requirement, write the truth table like table 1

Input output

L1 H1 L2 H2 Y M

0 0 0 0 0 0

1 0 0 0 1 0

0 1 0 0 0 0

X 1 1 0 0 1

X 1 1 1 0 0

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 Analyzing the logic expression of Y according to the truth table, we can conclude that the
operation of Y is only relative to the situation L1 and H1，so the starting condition for Y is ：

Y = L1﹒ H1

Change it into ladder diagram like fig3

fig 3 The logic ladder diagram for starting condition of Y

Considering the self-locking when Y is operating，correction Y’s control logic relationship

like this:

Y = （L1+Y）﹒ H1

The corresponding ladder diagram is like fig 4

fig4 the ladder diagram for Y operating

so，The starting and operating conditions for M can be derived:

starting：M = L2﹒H1﹒ H2

operating：M = （L2﹒H1+M）﹒ H2

The corresponding ladder diagram is like fig 5

fig 5 ladder diagram for M

2.PLC program

The expressions and the ladder diagrams received by logic relations can’t be downloaded
to PLC. Only when these symbols have certain relations with PLC’s input/output relays, PLC can

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execute all the control commands. The detail method to realize it is to distribute I/O first and
then connecting

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1 I/O distribution

I/O distribution is to distribute the input/output terminals according to the switching

loads. Note that some switches whose function are similar may be connected to PLC after series
or parallel connection. So the numbers for switches may not equal to the numbers for plc’ I/O
terminals.

Table 2 I/O distribution for example 1

Input output

Signal name Corresponding PLC terminal Signal name Corresponding PLC terminal

L1 I0.0 Y Q0.0

H1 I0.1 M Q0.1

L2 I0.2

H2 I0.3

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2 Use the relays in PLC to replace the symbols to yield PLC control program like fig6

fig 6 PLC control ladder diagram

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Functions and Instructions of a PLC
 Relay-type (Basic) instructions: I, O, OSR (1 shot rising), SET, RES, T, C
 Data Handling Instructions:
Data move Instructions: MOV, COP, FLL, TOD, FRD, DEG, RAD (degrees to radian).
Comparison instructions: EQU (equal), NEQ (not equal), GEQ (greater than or equal),
GRT (greater than).
Mathematical instructions: ADD,SUB, DIV,MUL, Continuous Control Instructions
(PID instructions).
Program flow control instructions: MCR (master control reset), JMP, LBL, JSR, SBR,
RET, SUS, REF
 Specific instructions: BSL, BSR (bit shift left/right), SQO (sequencer output), SQC
(sequencer compare), SQL (sequencer load).
 High speed counter instructions: HSC, HSL, RES, HSE
 Communication instructions: MSQ, SVC
 ASCII instructions: ABL, ACB, ACI, ACL, CAN
Timers
Timers are devices that count increments of time. Traffic lights are one example where timers are
used.
Timers are represented by boxes in ladder logic. When a timer receives an enable, the timer starts
to time. The timer compares its current time with the preset time. The output of the timer is a
logic 0 as long as the current time is less than the preset time. When the current time is greater
than the preset time the timer output is a logic 1.
S7-200 uses three types of timers: On-Delay(TON), Retentive On-Delay (TONR), and Off-Delay
(TOF).

S7-200 timers are provided with resolutions of 1 millisecond, 10milliseconds, and 100
milliseconds. The maximum value of these timers is 32.767 seconds, 327.67 seconds, and 3276.7
seconds, respectively. By adding program elements, logic can be programmed for much greater
time intervals.
On-Delay (TON)
When the On-Delay timer (TON) receives an enable (logic 1) at its input (IN), a predetermined
amount of time (preset time - PT) passes before the timer bit (T-bit) turns on. The T-bit is a logic
function internal to the timer and is not shown on the symbol. The timer resets to the starting
time when the enabling input goes to a logic 0.

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When the switch is closed input 4 becomes a logic 1, which is loaded into timer T37. T37 has a
time base of 100 ms (.100seconds). The preset time (PT) value has been set to 150. This is
equivalent to 15 seconds (.100 x 150). The light will turn on 15seconds after the input switch is
closed. If the switch were opened before 15 seconds had passed, then reclosed, the timer would
again begin timing at 0.
By reprogramming the T37 contact as a normally closed contact, the function of the circuit is
changed to cause the indicator light to turn off only when the timer times out. This function
change was accomplished without changing or rewiring I/O devices.

Retentive On-Delay (TONR)

The Retentive On-Delay timer (TONR) functions in a similar manner to the On-Delay timer
(TON). There is one difference. The Retentive On-Delay timer times as long as the enabling
input is on, but does not reset when the input goes off. The timer must be reset with a RESET (R)
instruction.
The same example used with the On-Delay timer will be used with the Retentive On-Delay
timer. When the switch is closed at input I0.3, timer T5 (Retentive timer) begins timing. If, for
example, after 10 seconds input I0.3 is opened the timer stops. When input I0.3 is closed the
timer will begin timing at 10seconds. The light will turn on 5 seconds after input I0.3 has been
closed the second time. A RESET (R) instruction can be added. Here a pushbutton is connected

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to input I0.2. If after 10seconds input I0.3 were opened, T5 can be reset by momentarily closing
input I0.2. T5 will be reset to 0 and begin timing from 0 when input I0.3 is closed again.

Off-Delay (TOF)
The Off-Delay timer is used to delay an output off for a fixed period of time after the input turns
off. When the enabling bit turns on the timer bit turns on immediately and the value is set to 0.
When the input turns off, the timer counts until the preset time has elapsed before the timer bit
turns off.

Example 1
The next figure represents the process of making tea every day in the morning for seven days
(water in the tank is enough for 7 days only)
Procedure:
When pressing the ‘start’ button, the valve 1 (V1) opens, so the water pass through the valve to
the heating tank. And when the water level reaches the float switch (FS), the valve should close
and heating must begin.
When the temperature reach the required level the thermostat disconnects the heater and opens
valve 2 (V2) for 10 seconds then the alarm bell is activated (as a sign that the tea jug is filled
now with hot water).

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Example 2
In the following example a tank will be filled with two chemicals, mixed, and then drained.
When the Start Button is pressed at input I0.0, the program starts pump 1 controlled by output
Q0.0. Pump 1 runs for 5 seconds, filling the tank with the first chemical, then shuts off. The
program then starts pump2, controlled by output Q0.1. Pump 2 runs for 3 seconds filling the tank
with the second chemical. After 3 seconds pump 2 shuts off. The program starts the mixer motor,
connected to output Q0.2 and mixes the two chemicals for 60 seconds. The program then opens
the drain valve controlled by output Q0.3, and starts pump 3 controlled by output Q0.4. Pump 3
shuts off after 8 seconds and the process stops. A manual Stop switch is also provided at input
I0.1.

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Counters
Counters used in PLCs serve the same function as mechanical counters. Counters
compare an accumulated value to a preset value to control circuit functions.
Control applications that commonly use counters include the following:
 Count to a preset value and cause an event to occur
 Cause an event to occur until the count reaches a preset value
A bottling machine, for example, may use a counter to count bottles into groups of
six for packaging.

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Counters are represented by boxes in ladder logic. Counters increment/decrement one count each
time the input transitions from off (logic 0) to on (logic 1). The counters are reset when a
RESET instruction is executed. S7-200 uses three types of counters: up counter (CTU), down
counter (CTD), and up/down counter (CTUD).

The conversion method from relay to PLC control program

Working steps

○
1 Distribute the Detecting Elements (such as limit switch)、button and so on Properly and
connected them to input terminals.

○
2 Connect the executive elements(such as electromagnetic valve ) to output terminals
○
3 Choose the corresponding element in PLC which have same function according to the relay
system
○
4 Fishing the ladder diagram
○
5 Debugging

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4.note!!
Connecting according to the hardware connecting diagram strictly

Example 2:
Requirement:

One worktable is in straight reciprocating motion .When press start button SB1, KM1 will pull in
and worktable forward. When meeting SQ1, KM1 will release at the same time KM2 will pull in
and the worktable reverse. When meeting SQ2, KM2 will release at the same time KM1 will
pull in and the

Worktable forward……when overload or pressing SB2, the worktable will stop anywhere.

1.Analyzing

It is used in practice widely. The main circuit and the relay control circuit is like fig8 and fig

fig 8 main circuit fig 9 control circuit

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2．I/O distribution：

table 3 I/O distribution

input Output

Start button SB1 I0.0 Forward drivingKM1 Q0.0

Stop button SB2 I0.1 Reverse driving KM2 Q0.1

Forward limit SQ1 I0.2

Reverse limit SQ2 I0.3

Thermal Protection FR I0.4

3．Design the hardware connecting

fig 10 PLC hardware connect

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4．Program

when programming use PLC，note carefully the normal-close contract (such as SB2 and FR ).

If connecting normal-close contract external (FR),you must use normal open contract in the
PLC program. It is not conformable to the relay control circuit.

In ladder diagram, the output coin must close to the right bus line. That is, it is forbidden to
connect any contract between the coin and the right bus line .So we must move the FR (after
KM1 and KM2 in relay control circuit) to left.

Fig 11 ladder diagram

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PLC Programming practice exercises
Exercise 1: FORWARD - STOP- REVERSE

The Motor is run in either direction by S2 or S3 and to change the direction one has to stop
motor by S1.

The motor control is characterized by

1. Latching: Q1 (NO) and Q2 (NO) are self latching i.e they continue the power to the
respective coils after push button is released. The characteristics of push button
switches is that it continues line while it is pressed and hold, but when released it
discontinues the line.

2. Interlocking: Q1 (NC) and Q2 (NC) are interlockers i.e they avoid short circuits. The
contact of the coil don’t close or open immediately after the coil is energized but there is
time delay which cause short circuit

Control Circuit Power Circuit

Problem:

a) Develop the FBD and LAD from the above control circuit

b) Draw a control circuit that allows the running of a motor to change its direction
with out stoppage of the motor

c) Develop the FBD and LAD from the control circuit of problem b

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Exercise 2: Car Parking lot

a) Develop a simple FBD using counter to understand the function of counter

b) Develop FBD program for a car parking lot that have the capacity of parking 12
cars as shown below in the figure

Problem c) modify your FBD to allow display the number of free and occupied lots

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 Chapter: Two
Industrial Sensors and Actuators
Sensors

 A sensor is any kind of device that converts a physical property into electrical properties.
 Physical properties are things like light intensity, position/speed, heat/temperature,
pressure etc.
 Electrical properties are things like Voltage and/or Current.
The benefit of a sensor in robots is that it allows our controller to obtain information about the
physical properties.
 The primary use of sensors in robots is:
1. To give to the robot information about its environment.
2. To give to the robot an information about itself.
In order to effectively use sensors in robotic systems, it’s important to know;
 How to select appropriate sensors
 How to read sensor data using the robotic controller
 How to convert the sensor data into information that can be used by the robotic controller
Some common and useful sensor types that are available in robotic systems;
1. Resistive Sensors
2. Capacitive sensors
3. Inductive/ magnetic sensors
4. Optical sensors
5. Piezoelectric sensors
6. Acoustic Sensors
1. Resistive Sensors
Sensors that detect a physical property by relating it to a change in resistance. Their resistance is
affected by a typical physical quantity.
Non-electrical input Electrical output
Variable Resistor

Some physical quantities that can be measured using resistive effects:

 Temperature
 Light
 Deformation
 Magnetic field strength
Resistance depends upon the shape, size, material properties and the environment of the resistive
material.

54
 Chapter: Two
Industrial Sensors and Actuators
Sensors

 A sensor is any kind of device that converts a physical property into electrical properties.
 Physical properties are things like light intensity, position/speed, heat/temperature,
pressure etc.
 Electrical properties are things like Voltage and/or Current.
The benefit of a sensor in robots is that it allows our controller to obtain information about the
physical properties.
 The primary use of sensors in robots is:
1. To give to the robot information about its environment.
2. To give to the robot an information about itself.
In order to effectively use sensors in robotic systems, it’s important to know;
 How to select appropriate sensors
 How to read sensor data using the robotic controller
 How to convert the sensor data into information that can be used by the robotic controller
Some common and useful sensor types that are available in robotic systems;
1. Resistive Sensors
2. Capacitive sensors
3. Inductive/ magnetic sensors
4. Optical sensors
5. Piezoelectric sensors
6. Acoustic Sensors
1. Resistive Sensors
Sensors that detect a physical property by relating it to a change in resistance. Their resistance is
affected by a typical physical quantity.
Non-electrical input Electrical output
Variable Resistor

Some physical quantities that can be measured using resistive effects:

 Temperature
 Light
 Deformation
 Magnetic field strength
Resistance depends upon the shape, size, material properties and the environment of the resistive
material.

55
  Potentiometric Sensors
Potentiometric sensors work by changing the length of the resistive element. Potentiometric
sensors have a wiper contact linked to a mechanical shaft that can be either angular (rotational)
or linear (slider type) in its movement, and which causes the resistance value between the
wiper/slider and the two end connections to change giving an electrical signal output that has a
proportional relationship between the actual wiper position on the resistive track and its
resistance value.

Fig.1: Construction of potentiometric sensors

Fig.2: Voltage divider circuit

These types of sensors provide a “positional” feedback. One method of determining a position is
to use either “distance”, which could be the distance between two points such as the distance
travelled or moved away from some fixed point, or by “rotation” (angular movement).

56
  Piezoresistive sensors
A Piezoresistive material is one that changes its resistivity when deformed.
 Thermoresistive sensors
A material that changes its resistance in response to a change in temperature. Metals and semi-
conductors have this effect.
From metals: Resistance thermometer
From semi-conductors: Thermister
 Optoresistive sensors
When light falls on a photo resistive material, free charge carriers are generated. Thus the
resistance of the sensor decreases as the light intensity increases.
e.g. The light dependent resistors (LDR)

2. Capacitive Sensors
Capacitive sensors are sensors that work by varying the electrical properties of capacitance.
Capacitance is the ability of a material to store electric charges.

Capacitance is related to voltage:

, where, Q=charge, C=capacitance an V=voltage

Physical capacitance Voltage

property

Capacitance is related to the physical distance between the plates, the cross sectional area of the
plates, and the permittivity of the material between the two plates.
,
Where C=capacitance=area between the two plates, d=distance between two plates,
=permittivity, =permittivity of free space, =dielectric constant of the material between plates.

Capacitive displacement sensors are essentially just parallel plate capacitors. The capacitance
will change if the plate separation changes, the area of overlap of the plates changes, or a slab of
dielectric is moved into or out of the plates. All these methods can be used to give linear
displacement sensors. The change in capacitance has to be converted into a suitable electrical
signal by signal conditioning.

57
 Fig.3. Capacitor sensors: (a) changing the plate separation,(b) changing the area of overlap,(c)
moving the dielectric
3. Inductive/ magnetic sensors
Inductive and magnetic sensors are sensors the relate physical properties into electrical
inductance and the change in magnetic fields. The most common type of inductive and magnetic
sensors that are used in robotic applications are displacement sensors specifically the proximity
sensors.
Proximity sensors are displacement sensors which are used to trigger when one object is comes
near to another object. Such as a reed switch.

Fig.4. Reed Switch

4. Optical Sensors
Optical sensors are working based on the principle of Optoresistivity.
Optoresistive sensors are made of materials that change their resistivity in response to the
intensity of light. This is called the “photo-resistive” effect. Optoresistive sensors are used to
measure the intensity of light.
 Light dependent resistors (LDR)
When light falls on a photo resistive material, free charge carriers are generated. Thus the
resistance of the sensor decreases as the light intensity increases.

58
  Photo sensors

Fig.5. Photo sensor structure

 Optical Encoders
The term encoder is used for a device that provides a digital output as a result of angular or linear
displacement. An increment encoder detects changes in angular or linear displacement from
some datum position, while an absolute encoder gives the actual angular or linear position.
The figure below shows the basic form of an incremental encoder for the measurement of
angular displacement. A beam of light, from perhaps a light-emitting diode (LED), passes
through slots in a disc and is detected by a light sensor, e.g. a photodiode or phototransistor.
When the disc rotates, the light beam is alternately transmitted and stopped and so a pulsed
output is produced from the light sensor. The number of pulses is proportional to the angle
through which the disc has rotated, the resolution being proportional to the number of slots on a
disc. With 60 slots then, since one revolution is a rotation of 360o, a movement from one slot to
the next is a rotation of 6o. By using offset slots it is possible to have over a thousand slots for
one revolution and so much higher resolution.

Fig.6. Basic form of an incremental encoder

59
The absolute encoder differs from the incremental encoder in having a pattern of slots which
uniquely defines each angular position. With the form shown in Figure 7, the rotating disc has
four concentric circles of slots and four sensors to detect the light pulses. The slots are arranged
in such a way that the sequential output from the sensors is a number in the binary code, each
such number corresponding to a particular angular position. With 4 tracks there will be 4 bits and
so the number of positions that can be detected is 24 = 16, i.e. a resolution of 360/16 = 22.5o.
Typical encoders tend to have up to 10 or 12 tracks. The number of bits in the binary number
will be equal to the number of tracks. Thus with 10 tracks there will be 10 bits and so the number
of positions that can be detected is 210, i.e. 1024, a resolution of 360/1024 = 0.35 o.

Fig.7. Basic form of an absolute encoder

5. Piezoelectric sensors
Piezoelectric materials develop a charge in response to deformation.

Piezoelectric sensors are used to detect the sound waves as a result of vibration.
6. Acoustic Sensors
 Ultrasonic sensors
Ultrasonic sensors are used to measure the displacement of an object by using sound waves.

Robot Actuators
• Actuators convert an electrical signal into a corresponding physical quantity such as
movement, force, sound etc.
1. The Electromechanical Relay
 Solenoids form the basis of a number of output control actuators. When a current passes
through a solenoid a magnetic field is produced and this can then attract ferrous metal

60
 components in its vicinity. One example of such an actuator is the relay, the term
contactor being used when large currents are involved.
 The term Relay generally refers to a device that provides an electrical connection
between two or more points in response to the application of a control signal. The most
common and widely used type of electrical relay is the electromechanical relay or EMR.

Fig. 8. The Electromechanical Relay

Fig. 9. Electrical Relay Construction

Fig.10. Relays used as an output device

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2. The Linear Solenoid
 Another type of electromagnetic actuator that converts an electrical signal into a
magnetic field is called the Linear Solenoid. The linear solenoid works on the same
basic principal as the electromechanical relay.
 Linear solenoid’s basically consist of an electrical coil wound around a cylindrical tube
with a ferro-magnetic actuator or “plunger” that is free to move or slide “IN” and “OUT”
of the coils body.

Fig.11. Construction and structure of a solenoid

3. Solenoid Valves
 Another example of the use of a solenoid as an actuator is a solenoid operated valve. The
valve may be used to control the directions of flow of pressurized air or oil and so used to
operate other devices such as a piston moving in a cylinder.
 A valve is a mechanical device for controlling the flow of a fluid or a substance. A
solenoid valve is an electromagnetic valve for use with liquid or gas controlled by
running or stopping an electrical current through a solenoid, which is a coil of wire, thus
changing the state of the valve.
 A solenoid valve has two main parts: the solenoid and the valve. The solenoid converts
electrical energy into mechanical energy which, in turn, opens or closes the valve
mechanically.
 Figure 12 shows one such form, a spool valve, used to control the movement of a piston
in a cylinder. Pressurized air or hydraulic fluid is inputted from port P, this being
connected to the pressure supply from a pump or compressor and port T is connected to
62
 allow hydraulic fluid to return to the supply tank or, in the case of a pneumatic system, to
vent the air to the atmosphere. With no current through the solenoid (Figure 12(a)) the
hydraulic fluid of pressurized air is fed to the right of the piston and exhausted from the
left, the result then being the movement of the piston to the left. When a current is passed
through the solenoid, the spool valve switches the hydraulic fluid or pressurized air to the
left of the piston and exhausted from the right. The piston then moves to the right. The
movement of the piston might be used
to push a deflector to deflect items off a conveyor belt (see Figure 12(b))or implement
some other form of displacement which requires power.

Fig.12. An example of a solenoid operated valve

 With the above valve there are the two control positions shown in Figure 12 (a) and (b).
Directional control valves are described by the number of ports they have and the number
of control positions. With the above valve there are the two control positions shown in
Figure 2.24(a) and (b). Directional control valves are described by the number of ports
they have and the number of control positions.

Fig.13. (a) The basic symbol for a two position valve, (b) the 4/2 valve

63
 Fig.14. Direction valves

In diagrams, the actuation methods used with valves are added to the symbol; Figure 2.27 shows
examples of such symbols. The valve shown in Figure 2.24 has a spring to give one position and
a solenoid to give the other and so the symbol is as shown in Figure 2.27(d).

Fig.15. Actuation symbols: (a) solenoid, (b) push button, (c) spring operated, (d) a 4/2 valve
 Direction valves can be used to control the direction of motion of pistons in cylinders, the
displacement of the pistons being used to implement the required actions.

4. DC Motors
 The DC Motor or Direct Current Motor to give it its full title, is the most commonly used
actuator for producing continuous movement and whose speed of rotation can easily be
controlled, making them ideal for use in applications were speed control, servo type
control, and/or positioning is required.
 Normal DC motors have almost linear characteristics with their speed of rotation being
determined by the applied DC voltage and their output torque being determined by the
current flowing through the motor windings. The speed of rotation of any DC motor can
be varied from a few revolutions per minute (rpm) to many thousands of revolutions per
minute making them suitable for electronic, automotive or robotic applications. By
connecting them to gearboxes or gear-trains their output speed can be decreased while at
the same time increasing the torque output of the motor at a high speed.

64
 Fig.16. DC Motor Construction
5. The DC Servo Motor
 A servo motor is a type of motor which rotates a certain angle for a given amount of
electrical input (Signal).This type of motor is basically a brushed DC motor with some
form of positional feedback control connected to the rotor shaft.
 Typical positional “Feedback” devices include Resolvers, Encoders and Potentiometers
as used in radio control models such as airplanes and Robots.
 A servo motor generally includes a built-in gearbox for speed reduction and is capable of
delivering high torques directly. The output shaft of a servo motor does not rotate freely
as do the shafts of DC motors because of the gearbox and feedback devices attached.

Fig.17. Parts of a Servo Motor

Fig.18. Construction of a Servo Motor

65
 Fig.19. DC Motor Switching and Control

Fig.20. Reversing the Direction of A DC Motor

6. The DC Stepper Motor

 Like the DC motor above, Stepper Motors are also electromechanical actuators that
convert a pulsed digital input signal into a discrete (incremental) mechanical
movement are used widely in industrial control applications.
 As it name implies, the stepper motor does not rotate in a continuous fashion like a
conventional DC motor but moves in discrete “Steps” or “Increments”, with the angle
of each rotational movement or step dependent upon the number of stator poles and
rotor teeth the stepper motor has.

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Fig.21. Construction of a DC Stepper motor

67
 Chapter 3
DCS and SCADA Systems
SCADA Systems

68
SCADA Hardware

SCADA and Local Area Networks

69
 Fig. Components of SCADA System
Distributed Control Systems (DCS)

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