Modbus Installation

and Instruction Manual

The information contained in this manual was current at the time of printing. The most current
versions of all Hydro Instruments’ manuals can be found on our website:
www.hydroinstruments.com
 Table of Contents

I. Background ...................................................................................................... 2

II. Definitions ....................................................................................................... 2

III. Support Types & Address Data Format ........................................................... 3

IV. Programming Equipment Onto the Network.................................................... 4

1. Omni-Valves (OV-110 and OV-1000)....................................................4
2. Vaporizers (VPH-10000) .....................................................................5
3. Gas Detectors (GA-180) ......................................................................5
4. Automatic Changeover Controller (CS-110) ..........................................6
5. Residual Analyzers (RAH-210, RPH-250, RPH-260, RAH-280, WQM-100)
6. Turbidimeter, Gas Detector, and PID Controller
(TH-4000, GA-171, and HC-220) .................7
V. Programming Masters...................................................................................... 7

VI. Troubleshooting ………………………………………………………………………………...31

TABLES............................................................................................................. 3-30

Table 1. Data Formats and Baud Rates Supported by Hydro Instruments .....3
Table 2. Wiring connections for Modbus RTU .............................................3
Table 3. Description of Function Codes for Hydro Instruments Equipment ....7
Table 4. Modbus OV-110 and OV-1000 Omni-valve ....................................8-9
Table 5. Modbus VPH-10000 Vaporizer ......................................................10
Table 6. Modbus GA-180 Gas Detector ......................................................11-12
Table 7. Modbus CS-110 Automatic Changeover Controller .........................12-13
Table 8. Modbus RAH-210 and RPH-250 Residual Analyzers ........................13-17
Table 9. Modbus TH-4000 Turbidimeter.....................................................17-18
Table 10. Modbus GA-171 Gas Detector ....................................................18-19
Table 11. Modbus HC-220 PID Controller ...................................................19-21
Table 12. Modbus WQM-100 Water Quality Monitor ....................................21-24
Table 13. Modbus RPH-260 Residual Analyzer ............................................24-27
Table 14. Modbus RAH-280 Residual Analyzer ............................................28-30

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 1

 Modbus Communication Set-up and Installation

I. Background

Modbus, developed in 1979, is a serial communications protocol to be used with programmable

logic controllers (PLCs) to read or write digital messages sent over the network. It is perhaps
one of the most widely used communication protocols as it is free to use, easy to program and
maintain, and was developed specifically for industrial use. Using a master/slave network, it
can transmit data in real time giving it an advantage over other networks. Modbus can support
up to 247 devices and is used to define both the physical layer (electrical connections) and the
application layer (way in which to communicate). All devices on the network must have the
same physical configuration consisting of the data format and baud rate.

Before setting up/installing the Modbus communication network onto Hydro Instruments
equipment, familiarize yourself with the information contained in this packet. If you have any
questions please contact Hydro Instruments.

Electrical W arning: Programming these devices does include electrical shock risk. Take care
to avoid electrical shocks and do not touch any part of the power line unless you are certain the
power has been disconnected.

II. Definitions

Physical Layer: The physical layer is the actual hardware and electrical termination set-up used
to connect the master and slaves together for Modbus communication. All Hydro Instruments
equipment outlined in this document supports “Modbus RTU” on a 2-wire RS-485 network.

Baud Rate: The baud rate is the modulation of the signal between devices.

Node: The node is the programmed number given to the slave so that the master can
communicate specifically with that unit when requested. Thus, each unit should have its own
unique node number.

Application Layer: This is the layer closest to the end user. It interacts with the software
application to display information in a human-recognizable format.

Master: The master is the main controller of the network (some programmers may be more
familiar with the “server”). There can only be one master per network which is the only device
that can read and write information to the other devices (or slaves). The master may be a
computer or any type of SCADA system.

Slave: The slave, or “client”, is any PLC connected to the master. Each slave will have a
specific node which will be used by the master to communicate to that specific PLC.

Function Code: The function code tells the slave what type of information is being requested
by the master. This information may either be to read or write bits, or to read or write
registers. The function code is an integer from 1 to 127 and that number is interpreted by the
slave as to what information is requested. Thus, the same function code may serve two
different purposes on two different instruments.

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 2

Data Address: The data address in decimal format is an indexing integer uniquely identifying
each variable stored by the selected device.

Data Quantity: The data quantity tells the slave how many bits or registers of data are going to
the data address.

III. Support Types (Physical/Electrical Standards)

1. R S-485

The RS-485 network is supported by Hydro Instruments equipment and is the most commonly
used physical layer. It allows for connection to multiple slaves (up to 247), has excellent noise
immunity, high speed (up to 35Mbps), and cables can be used up to 4,000 feet. The RS-485
version of Modbus is commonly referred to as Modbus RTU. Aside from the physical
connections, the user must define the baud rate and the data format so that both the master
and the slave have the same format. The data formats and baud rates that are supported can
be seen in Table 1.

2. Address Data Format - The published Modbus addresses are decimal addresses and
use the standard notation prefix for decimal (no prefix).

Table 1. Data Formats and Baud Rates Supported by Hydro Instruments

Data Format Baud Rates

8/N/1 2400
8/N/2 4800
8/E/1 9600
8/O/1 19200
38400
57600
115200
250000

Hydro Instruments uses a half-duplex (2 wire) interface type. Hydro Instruments also
recommends that the slaves be “daisy chained” together so that only one connection to the
master is required. Cat 5 cable is the recommended cable to use and the wiring should be
installed according to Table 2.

Table 2. Wiring connections for Modbus RTU

CAT 5 Cable RS-485 Terminal Equipment Terminal

Brown & white V+
Blue &white A A
Blue B B
Brown V-(GND) GND

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 3

 The RS-485 network requires a “termination resistor” installed at either end of the network
when using very long cable runs (>300 feet) at high baud rates (> 19200). Contact Hydro
Instruments for more information.

3. TCP / IP

This network architectural model can be used to communicate through Ethernet or WiFi and has
the advantage of being able to control Modbus devices over the internet. This version is
referred to as Modbus TCP/IP. Hydro Instruments does not currently sell the devices for this
communication and recommends using an intermediate hub which can connect to the RS-485
terminal. The user can then communicate to the hub using the configuration outlined in
Section III.1, and then communicate to this hub over the internet. Contact your supplier for
installation information.

IV. Programming Equipment onto the Network:

1. Programing Omni-Valves (OV-110 and OV-1000)

Programming Omni-valves (slaves) should be performed after the physical layer has been
installed (Section III). Omni-valves purchased after October 2013 will be standard equipped to
communicate with Modbus. If purchased before said date, contact Hydro Instruments.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press the “down” key until the password screen appears. Enter
the password, “110” (OV-110) or “1000” (OV-1000) using the “plus” and “minus” keys.
III. Once the correct password appears on the screen, continue to press the down key until
the text “ADCAL” is blinking, then press the plus key.
IV. Press the down key once so that “Yes” is blinking. Press and hold the “down” key for
approximately 5-10 seconds.
V. A new set of screens should appear. Go down two screens using the “down” key until
the “Modbus” screen appears.
VI. Use the “plus” key to select the baud rate.
VII. Press the “down” key once. Then enter the node number using the “plus” key. Save
this number to program the master controller and to ensure the same number is not
given to two units.
VIII. Press the “down” key once. Then enter the data format using the “plus” key.
IX. Cycle the power to save the information.

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 4

 2. Programming Vaporizers (VPH-10000)

Programming Vaporizers should be performed after the physical layer has been installed
(Section III). Refer to the steps below to configure the VPH-10000 vaporizer baud rate, node
number and data format to communicate with the network.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press the “down” key until the password screen appears. Enter
the password “100” using the “plus” and “minus” keys.
III. Once the correct password is blinking continue to press the down key until the Modbus
screen appears.
IV. Using the “plus” and “minus” keys, enter the baud rate that matches the master/server.
V. Press the “down” key so that the node number is blinking and enter the node number
using the “plus” and “minus” keys. Save this number and make sure it does not match
with any other equipment on the network.
VI. Press the “down” key so that the data format is blinking. Enter the data format that
matches the master/server.
VII. Cycle the power to save the information.

3. Programming GA-180 Gas Leak Detectors

Programming the GA-180 Gas Detectors should be performed after the physical layer has been
installed (Section III). Refer to steps below (and GA-180 O&M Manual Figure 8) to configure the
GA-180 baud rate, node number, and data format to communicate with the network.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press the “down” key until the password screen appears.
Enter the password “180” using the “plus” and “minus” keys.
III. Once the correct password is blinking press the down arrow key. Then with “Sensor”
blinking, press and hold the “minus” key until the Modbus setup screen appears.
IV. Using the “plus” and “minus” keys, enter the baud rate that matches the
master/server.
V. Press the “down” key so that the node number is blinking and enter the node
number using the “plus” and “minus” keys. Save this number and make sure it does
not match with any other equipment on the network.
VI. Press the “down” key so that the data format is blinking. Enter the data format that
matches the master/server.
VII. Cycle the power to save the information.

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 4. Programming CS-110 Automatic Changeover Controller

Programming the CS-110 Automatic Changeover controllers should be performed after the
physical layer has been installed (Section III). Refer to steps below (and CS-110 O&M Manual)
to configure the CS-110 baud rate, node number, and data format to communicate with the
network.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press the “down” key until the password screen appears.
Enter the password “110” using the “plus” and “minus” keys.
III. Once the correct password is blinking press the down arrow key. Then continue to
press the “down” key until the Modbus setup screen appears.
IV. Using the “plus” and “minus” keys, enter the baud rate that matches the
master/server.
V. Press the “down” key so that the node number is blinking and enter the node
number using the “plus” and “minus” keys. Save this number and make sure it does
not match with any other equipment on the network.
VI. Press the “down” key so that the data format is blinking. Enter the data format that
matches the master/server.
VII. Cycle the power to save the information.

5. Programming RAH-210, RPH-250, RPH-260, RAH-280, and WQM-100

Analyzers

Programming the Residual Analyzers should be performed after the physical layer has been
installed (Section III). Refer to steps below (and O&M Manuals) to configure the residual
analyzer baud rate, node number, and data format to communicate with the network.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press and hold the “down” key for at least 5 seconds until the
first hidden screen appears. Use the “down” key to navigate to the 12th hidden
screen which is the Modbus setup screen.
III. Using the “plus” and “minus” keys, enter the baud rate that matches the
master/server.
IV. Press the “down” key so that the node number is blinking and enter the node
number using the “plus” and “minus” keys. Save this number and make sure it does
not match with any other equipment on the network.
V. Press the “down” key so that the data format is blinking. Enter the data format that
matches the master/server.
VI. Cycle the power to save the information.

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 6

 6. Programming TH-4000 Turbidimeter, GA-171 Gas Detector, HC-220 PID
Controller

Programming the TH-4000 Turbidimeter, GA-171 Gas Detector, or HC-220 PID Controller should
be performed after the physical layer has been installed (Section III). Refer to steps below to
configure the baud rate, node number, and data format to communicate with the network.

I. Determine the baud rate and data format of the master controller.
II. From the main screen, press and hold the “down” key for at least 5 seconds until the
Modbus setup screen appears.
III. Using the “plus” and “minus” keys, enter the baud rate that matches the
master/server.
IV. Press the “down” key so that the node number is blinking and enter the node
number using the “plus” and “minus” keys. Save this number and make sure it does
not match with any other equipment on the network.
V. Press the “down” key so that the data format is blinking. Enter the data format that
matches the master/server.
VI. Cycle the power to save the information.

V. Programming Masters:

Be sure that the electrical terminations are complete and accurate. Also confirm that the baud
rate and data format are the same on the master as they are on the slaves. Different software
may have different ways of displaying and programming information on the device, however
the function code and addresses for the specified equipment will be the same regardless of the
software being used. Refer to the tables below for setting the equipment parameters on the
master/server.

Function Code Designations:

Table 3. Description of Function Codes for Hydro Instruments Equipment

Function Request Response

Function Name Description
Code Packet Size Packet Size
01 read coils read 1 to 2000 bits 8 5 or 6 + N/8
02 read discrete inputs read 1 to 2000 bits 8 5 or 6 + N/8
03 read hold registers read 1 to 125 registers 8 5 + 2N
04 read input registers read 1 to 125 registers 8 5 + 2N
05 write a single coil write 1 bit 8 8
06 write a single register write 1 register 8 8
15 write multiple coils write 1 to 2000 bits 9 or 10 + N/8 8
16 write multiple registers write 1 to 123 registers 9 + 2N 8

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 7

VARIABLE ADDRESSES AND REGISTER VALUES

*Values are read only and cannot be edited by the user.

**The decimal positions can be read but should not be written over Modbus since they can
only be changed on the display.

The variable type defines whether or not the data stored in the register is a real time
value/number (float/floating point) or if the number will correspond to a feature or command
(integer). In the case of integers, values have been developed so that the Omni-valve can
change and display features like units, the control type, or control alarms and relays over the
Modbus network. The following definitions for integer type values can be seen in table 5.

The Omni-valve integer type values correspond to Modbus registers. The Omni-valve float
values correspond to two Modbus registers in which the float data is in the IEEE 754 format (32
bit). Using this format the first address reads/writes the most significant 16 bits, whereas the
second address reads/writes the least significant 16 bits.

Table 4. Modbus OV-110 and OV-1000 Omni-valve

Variable Addresses, Register Values, and Features

Register
Name Type Address Feature
Value
0 Automatic
Run Mode Integer 0 1 Manual
2 Check Valve Position
0 Normal
1 Flow Signal Loss
2 Low Flow
3 Res/ORP Loss
Alarm Status Integer 1
4 Low Residual
5 High Residual
6 Flow + Resl Loss
7 Dose Signal Loss
0 Flow Pacing
1 Residual/ORP
Control Method Integer 2 2 Compound Loop
3 Step Feed
4 Dual Input Feed Fwd
0 %
1 GPM
2 MGD
Process Variable 1 Units Integer 3 3 LPM
4 MLD
5 GPD
6 m3/hr
0 ppm
Process Variable 2 Units Integer 4 1 mg/l
2 mV

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 8

 3 pH
4 GPD
0 %
1 PPD
2 g/hr
3 kg/hr
Process Output 1 Units Integer 5 4 GPH
5 GPM
6 GPD
7 LPM
8 LPH
*PV1 Float 6/7
PV1 Dosage Float 8/9
PV1 Span Float 10/11
PV1 Low Set Float 12/13
*PV2 Float 14/15
PV2 Set Point Float 16/17
PV2 Span Float 18/19
PV2 Integral Float 20/21
PV2 Low Set Float 22/23
PV2 High set Float 24/25
*PO1 Float 26/27
PO1 Span Float 28/29
PO1 Manual Float 30/31
*PV3 Float 32/33
PV3 Set Point Float 34/35
PV3 Span Float 36/37
PV3 Integral Float 38/39
PV1 Enable Integer 51 0 = Modbus, 1 = 4-20mA input
PV2 Enable Integer 52 0 = Modbus, 1 = 4-20mA input
PV3 Enable Integer 53 0 = Modbus, 1 = 4-20mA input
PV2 Lag Time Mode Integer 54 0 = fixed, 1 = single point, 2 = 2 point
PV2 F1 Integer 55
PV2 T1 Integer 56 Time in Seconds
PV2 F2 Integer 57
PV2 T2 Integer 58 Time in Seconds
PV3 Lag Time Mode Integer 59 0 = fixed, 1 = single point, 2 = 2 point
PV3 F1 Integer 60
PV3 T1 Integer 61 Time in Seconds
PV3 F2 Integer 62
PV3 T2 Integer 63 Time in Seconds
PO1 GFM Integer 64 In PO1 Units
PO1 GFM Span Integer 65 In PO1 Units
PO1 GFM Error Integer 66 10% to 100%
*Values are read only and cannot be edited by the user. However, PV1, PV2, and PV3 can each
be selected to either be read at the analog input channels or set over Modbus.

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 9

 Table 5. Modbus VPH-10000 Vaporizer
Variable Addresses, Register Values, and Features

Register
Name Type Address Feature
Value
*Gas Temperature Integer 1
*Gas Pressure Integer 2
Gas Pressure Span Integer 3
High Pressure Alarm Level Integer 4
*Superheat Temperature Integer 5
Superheat Alarm Set Point Integer 6
*Control Water Temperature Integer 7
Water Temperature Set Point Integer 8
High Temperature Alarm Set Point Integer 9
Low Temperature Alarm Set Point Integer 10
*Aux Water Temperature Integer 11
0 Normal
1 High
*Water Level Integer 12
2 Low
3 Low Low
*Heater Power Output (kW) Integer 13
*Heater Power Output (%) Integer 14
*Heater Element Temperature Integer 15
0 Celsius
Temperature Units Integer 16
1 Fahrenheit
0 PSI
Pressure Units Integer 17
1 Bar
0 Normal
2 Low Water Temperature
3 High Water Temperature
4 Heater Over Temperature
5 Superheat Alarm
*Alarm Status Integer 18 6 High Water Alarm
7 Low Water Alarm
8 PRV Burst Disc
EXP Burst Disc High
9
Pressure
10 High Pressure
*Values are read only and cannot be edited by the user.

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 10

 Table 6. Modbus GA-180 Gas Detector
Variable Addresses, Register Values, and Features

Name Type Address Description

Array holds all 16
Array of 1 through For example
*SensorLive(1 through 16) live sensor values
Integers 16 75 = 7.5ppm
(ppm or %)
Array holds the sensor configuration for all 16
sensors. Each integer value is a bit field, with the
following fields:
Array of
17 b23-b16 = Filter Time
Integer
SensorType(1 through 16) through b15-b8 = Alarm Delay Time
Bit
32 b6 = Engineering Units (0=ppm, 1=%)
Fields
b5 = Latch Enable
b4 = Fail Safe Enable
b3-b0 = Gas Type
b23
b22
b21
b20
b19
b18
b17
b16
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
Filter Time Alarm Delay Time Gas Type

Fail Safe Enable

Latch Enable
Engineering Units

Gas Type Integer

b3
b2
b1
b0

0 0 0 0 = 0  Sensor Off
0 0 0 1 = 1  NH3 (Ammonia)
0 0 1 0 = 2  O2 (Oxygen)
0 0 1 1 = 3  O3 (Ozone)
0 1 0 0 = 4  SO2 (Sulfur dioxide)
0 1 0 1 = 5  Cl2 (Chlorine)
0 1 1 0 = 6  ClO2 (Chlorine dioxide)
0 1 1 1 = 7  CO (Carbon monoxide)
1 0 0 0 = 8  H2 (Hydrogen)
1 0 0 1 = 9  H2S (Hydrogen sulfide)

33
Array of Array holds all 16 For example
SensorSpan(1 through 16) through
Integers sensor span values 100 = 10.0ppm
48
Integer Value Status
0 Off
49 Array holds all
Array of 1 Normal
*SensorStatus(1 through 16) through 16 sensor
Integers 2 Danger
64 status values
3 Alarm
4 Error
65
Array of Array holds all 16 For example
LowAlarm(1 through 16) through
Integers sensor low alarm values 10 = 1.0ppm
80
HighAlarm(1 through 16) Array of 81 Array holds all 16 For example

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 Integers through sensor high alarm 20 = 2.0ppm
96 values
Live temperature from
For example
*Temperature Integer 97 thermocouple
75 = 75F
(C or F)
Integer Value Status
Temperature 0 Normal
*TempStatus Integer 98
status 1 High Temp
2 Error
A bit field which holds the temperature
configuration:
Integer 99, 100,
TempSetup b16 = Temp Units (0=C, 1=F)
Bit Field 101
b15-b8 = Alarm Delay Time
b7-b0 = High Alarm Temp (C or F)
b16
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
Alarm Delay Time High Alarm Temp

Temp Units

Remote Set to 1 to remote

RemoteAck Integer 102
acknowledge acknowledge alarm
Indicates any Integer Value Status
*AnyLowAlarm Integer 103 sensor low 0 No Alarm
alarm 1 Any Alarm
Indicates any Integer Value Status
*AnyHighAlarm Integer 104 sensor high 0 No Alarm
alarm 1 Any Alarm
Indicates any Integer Value Status
*AnyFailAlarm Integer 105 sensor fail 0 No Alarm
alarm 1 Any Alarm
*Values are read only and cannot be edited by the user.

Table 7. Modbus CS-110 Automatic Changeover Controller

Variable Addresses, Register Values, and Features

Name Type Address Description

Integer Value State
0 Off
*V1State Integer 1
1 On
2 Empty
V1RunMins Integer 2 Run time in minutes
*V1Scale Float 3,4 Scale reading (e.g., 868 kg)
V1ScaleSpan Float 5,6 Scale span value (e.g., 1,000 kg)
Integer Value State
0 Off
*V2State Integer 11
1 On
2 Empty
V2RunMins Integer 12 Run time in minutes
*V2Scale Float 13,14 Scale reading (e.g., 868 kg)

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 12

 V2ScaleSpan Float 15,16 Scale span value (e.g., 1,000 kg)
Integer Value Setting
ScaleUnits 0 Off
Integer 20
(Enable / Scale Units) 1 Kg (kilograms)
2 Pd (pounds)
OnDelayTime Integer 21 Valve turn on delay time in seconds
Set to 1 to remote
RemoteAck Integer 22 Remote acknowledge
acknowledge alarm
Remote Integer Value Behavior
control 0 Turn OFF both valves
***RemoteCtrl Integer 23
for 1 Turn ON valve 1
valves 2 Turn ON valve 2
*Values are read only and cannot be edited by the user.
***Value is not persistent, and the command is ignored when tanks are empty.

Table 8. Modbus RAH-210 and RPH-250 Residual Analyzers

Variable Addresses, Register Values, and Features

Name Type Address Description

Temperature live displayed For example

*Temp Integer 1
(C or F) 74 = 74F

For example
Temp manual
TempManual Integer 2 2555 = 255.5K, display
(Kelvin x 10)
still shows C or F
Integer Value Setting
TempMode Integer 3 Temp mode 0 Auto
1 Manual
Integer Value Setting
TempUnits Integer 4 Temp units 0 C (Celsius)
1 F (Fahrenheit)
pH live calibrated value For example
*Ph Integer 10
(pH x 100) 425 = 4.25 pH
Integer Value Setting
0 Auto
PhMode Integer 11 pH mode 1 Manual
2 Monitor
3 None
PhFilterTime Integer 12 pH average filter time in seconds
pH manual value For example
PhManual Integer 13
(pH x 100) 425 = 4.25 pH
pH low alarm value For example
PhLow Integer 14
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
PhHigh Integer 15
(pH x 100) 425 = 4.25 pH
Hexadecimal Value Float Scale Factor
Flow 0x50 x1
**FlowDP Hex 20 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000

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 Flow Integer 21 Flow live
FlowSpan Integer 22 Flow span
FlowThreshold Integer 23 Flow threshold for PO1Flow
FlowMinCLC Integer 24 Flow min to stop Resl in CLC mode
Percent of FlowSpan below For example
FlowStop Integer 25
which stop 10 = 10% of span
FlowLow Integer 26 Flow low alarm value (0=Off)
Integer Value Setting
0 %
1 GPM
2 MGD
FlowUnits Integer 27
3 LPM
4 MLD
5 GPD
6 m3/hour
Flow dosage value For example
FlowDosage Integer 28
(% x 100) 125 = 1.25%
FlowFilterTime Integer 29 Flow average filter time in seconds
Hexadecimal Value Float Scale Factor
Turb1 0x50 x1
**Turb1DP Hex 30 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
*Turb1 Integer 31 Turb1 live (turbidity)
Integer Value Setting
Turb1Mode Integer 32 Turb1 mode 0 Off
1 On
Turb1Span Integer 33 Turb1 span
Turb1High Integer 34 Turb1 high alarm value
Hexadecimal Value Float Scale Factor
Turb2 0x50 x1
**Turb2DP Hex 40 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
*Turb2 Integer 41 Turb2 live (turbidity)
Integer Value Setting
Turb2Mode Integer 42 Turb2 mode 0 Off
1 On
Turb2Span Integer 43 Turb2 span
Turb2High Integer 44 Turb2 high alarm value
Hexadecimal Value Float Scale Factor
Residual 0x50 x1
**ReslDP Hex 50 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
*Resl Integer 51 Residual final calibrated value
ReslSetPoint Integer 52 Residual set point for PID ctrl
ReslLow Integer 53 Residual low alarm value (0=Off)
ReslHigh Integer 54 Residual high alarm value
ReslSpan Integer 55 Residual span
ReslMode Integer 56 Residual sensor Integer Value Setting

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 mode 0 mV cell
1 4/20mA sensor
Integer Value Setting
ReslUnits Integer 57 Residual units 0 PPM
1 MG/L
Residual integral value For example
ReslIntegral Integer 58
(% x 10) 225 = 22.5%
ReslFilterTime Integer 59 Residual average filter time in seconds
Hexadecimal Value Float Scale Factor
PO1 0x50 x1
**PO1DP Hex 60 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
PO1 Integer 61 PO1 final calibrated value
PO1Manual Integer 62 PO1 manual
PO1Span Integer 63 PO1 span
Integer Value Setting
0 %
1 PPD
2 GR/H
PO1Units Integer 64 PO1 units
3 KG/H
4 GPH
5 GPM
6 GPD
Integer Value Setting
PO1GasType Integer 65 PO1 gas type 1 Cl2
-1 SO2
Flag Bit Alarm Condition
b0 High Turbidity 1
b1 High Turbidity 2
b2 Turbid 1 Signal Loss
b3 Turbid 2 Signal Loss
b4 Low Flow
b5 Flow Signal Loss
Alarm status
AlarmStatus Integer 70 b6 Data Log Error
flag bits
b7 Thermistor Failure
b8 High Residual
b9 Low Residual
b10 Res/ORP Signal Loss
b11 High pH
b12 Low pH
b13 I/O Node COM Error
Integer Value Setting
Alarm mode
AlarmMode Integer 71 0 No Latch
setting
1 Latch
AlarmTime Integer 72 Alarm delay time in seconds
Integer Value Setting
Relay 0 Resl High Alarm
Relay1Mode Integer 80 mode 1 Resl Low Alarm
setting 2 Turbid 1 High Alarm
3 Turbid 2 High Alarm

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 15

 4 pH High/Low Alarm
5 Any Alarm
Integer Value Setting
0 Resl High Alarm
Relay 1 Resl Low Alarm
Relay2Mode Integer 81 mode 2 Turbid 1 High Alarm
setting 3 Turbid 2 High Alarm
4 pH High/Low Alarm
5 Any Alarm
Integer Value Setting
0 Resl High Alarm
Relay 1 Resl Low Alarm
Relay3Mode Integer 82 mode 2 Turbid 1 High Alarm
setting 3 Turbid 2 High Alarm
4 pH High/Low Alarm
5 Any Alarm
Integer Value Setting
0 Resl High Alarm
Relay 1 Resl Low Alarm
Relay4Mode Integer 83 mode 2 Turbid 1 High Alarm
setting 3 Turbid 2 High Alarm
4 pH High/Low Alarm
5 Any Alarm
Relay1 Integer 84 Relay 1 state
Relay2 Integer 85 Relay 2 state
Relay3 Integer 86 Relay 3 state
Relay4 Integer 87 Relay 4 state
DataLogEnb Integer 90 Data log enable
DataLogTime Integer 91 Data log time interval in seconds
Integer Value Setting
0 Resl
1 Temp
AO1 mode
AO1Mode Integer 100 2 pH
setting
3 Turb 1
4 Turb 2
5 PO1
Integer Value Setting
0 Resl
1 Temp
AO2 mode
AO2Mode Integer 101 2 pH
setting
3 Turb 1
4 Turb 2
5 PO1
Integer Value Setting
0 Resl
1 Temp
AO3 mode
AO3Mode Integer 102 2 pH
setting
3 Turb 1
4 Turb 2
5 PO1
AO4Mode Integer 103 AO4 mode Integer Value Setting

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 16

 setting 0 Resl
1 Temp
2 pH
3 Turb 1
4 Turb 2
5 PO1
Integer Value Setting
Run mode
RunMode Integer 110 0 Auto
setting
1 Manual
Integer Value Setting
0 Off
CtrlMode Integer 111 Control mode 1 Flow
2 Resl
3 Compound
*Values are read only and cannot be edited by the user.
**The decimal positions can be read but should not be written over Modbus since they can
only be changed on the display.

Table 9. Modbus TH-4000 Turbidimeter

Variable Addresses, Register Values, and Features

Name Type Address Description

Hexadecimal Value Float Scale Factor
Turb1 0x50 x1
**Turb1DP Hex 1 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
*Turb1 Integer 2 Turb1 live
Turb1Mode Integer 3 Turb1 mode (on or off)
Turb1Span Integer 4 Turb1 span level
Turb1High Integer 5 Turb1 high alarm level
Turb1AvgTime Integer 6 Turb1 average filter time in seconds
Hexadecimal Value Float Scale Factor
Turb2 0x50 x1
**Turb2DP Hex 11 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
*Turb2 Integer 12 Turb2 live
Turb2Mode Integer 13 Turb2 mode (on or off)
Turb2Span Integer 14 Turb2 span level
Turb2High Integer 15 Turb2 high alarm level
Turb2AvgTime Integer 16 Turb2 average filter time in seconds
Flag Bit Alarm Condition
b0 High Turbidity 1
b1 High Turbidity 2
AlarmStatus Integer 20 Alarm status flag bits b2 Turbid 1 Signal Loss
b3 Turbid 2 Signal Loss
b4 Data Log Error
b5 I/O Node COM Error
AlarmMode Integer 21 Alarm mode setting Integer Value Setting

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 17

 0 No Latch
1 Latch
AlarmTime Integer 22 Alarm delay time in seconds (set by user)
Relay1 Integer 30 Relay 1 state
Relay2 Integer 31 Relay 2 state
DataLogEnb Integer 40 Data log enable
DataLogTime Integer 41 Data log time interval in seconds
*Values are read only and cannot be edited by the user.
** The decimal positions can be read but should not be written over Modbus since they can
only be changed on the display.

Table 10. Modbus GA-171 Gas Detector

Variable Addresses, Register Values, and Features

Name Type Address Description

S1 live For example
*S1 Integer 1
(ppm x 10) 32 = 3.2ppm
S1 span For example
S1Span Integer 2
(ppm x 10) 32 = 3.2ppm
Integer Value Setting
0 Channel OFF -
1 NH3 Ammonia
2 O2 Oxygen
S1 3 O3 Ozone
S1GasType Integer 3 gas 4 SO2 Sulfur dioxide
type 5 Cl2 Chlorine
6 ClO2 Chlorine dioxide
7 CO Carbon monoxide
8 H2 Hydrogen
9 H2S Hydrogen sulfide
Integer Value Setting
S1AlarmMode Integer 4 S1 alarm mode 0 No Latch
1 Latch
S1 high alarm level For example
S1HighLevel Integer 5
(ppm x 10) 32 = 3.2ppm
S1AlarmTime Integer 6 S1 alarm delay time in seconds
S1FilterTime Integer 7 S1 averaging filter time in seconds
S2 live For example
*S2 Integer 11
(ppm x 10) 32 = 3.2ppm
S2 span For example
S2Span Integer 12
(ppm x 10) 32 = 3.2ppm
Integer Value Setting
0 Channel OFF -
1 NH3 Ammonia
S2 2 O2 Oxygen
S2GasType Integer 13 gas 3 O3 Ozone
type 4 SO2 Sulfur dioxide
5 Cl2 Chlorine
6 ClO2 Chlorine dioxide
7 CO Carbon monoxide

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 18

 8 H2 Hydrogen
9 H2S Hydrogen sulfide
Integer Value Setting
S2AlarmMode Integer 14 S2 alarm mode 0 No Latch
1 Latch
S2 high alarm level For example
S2HighLevel Integer 15
(ppm x 10) 32 = 3.2ppm
S2AlarmTime Integer 16 S2 alarm delay time in seconds
S2FilterTime Integer 17 S2 averaging filter time in seconds
Flag Bit Alarm Condition
b0 S1 High Alarm
b1 S2 High Alarm
AlarmStatus Integer 20 Alarm status flag bits
b2 S1 Loss Alarm
b3 S2 Loss Alarm
b4 I/O Node COM Error
*Values are read only and cannot be edited by the user.

Table 11. Modbus HC-220 PID Controller

Variable Addresses, Register Values, and Features

Name Type Address Description

Hexadecimal Value Float Scale Factor
PV1 0x50 x1
**PV1DP Hex 1 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
PV1 Integer 2 PV1 live
PV1 input selection (0=Modbus, 1=AI1, 2=AI2, 3=AI3,
PV1Select Integer 3
4=AI4)
Integer Value Setting
0 PV1
PV1Name Integer 4 PV1 name 1 H2O
2 PRO
3 FLO
Integer Value Setting
0 %
1 GPM
2 MGD
PV1Units Integer 5 PV1 units
3 LPM
4 MLD
5 GPD
6 m3/hour
PV1 dosage For example
PV1Dosage Integer 6
(dosage x 100) 125 = 1.25
PV1Span Integer 7 PV1 span
PV1MinCLC Integer 8 PV1 flow min in compound loop control mode
PV1 percent of
For example
PV1Stop Integer 9 span
3025 = 30.25%
below which

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 19

 stop
(% x 100)
PV1Threshold Integer 10 PV1 threshold
PV1FilterTime Integer 11 PV1 averaging filter time in seconds
PV1Low Integer 12 PV1 low alarm level
PV1VarLagTimeK1 Integer 13 PV1 Flow at variable lag time for PV1/PV2
PV1VarLagTimeK2 Integer 14 PV1 Flow at variable lag time for PV3
MaxLagTime1 Integer 15 PV1 max calculated lag time
LagTimeK1 Integer 16 PV1 user set lag time

MaxLagTime2 Integer 17 PV2 max calculated lag time

LagTimeK2 Integer 18 PV2 user set lag time
PV2DP Integer 20 PV2 Decimal position
PV2 Integer 21 PV2 live = residual
PV2 input selection (0=Modbus, 1=AI1, 2=AI2, 3=AI3,
PV2Select Integer 22
4=AI4)
0 = PV2, 1=RES, 2 =ORP, 3=pH,
PV2Name Integer 23 PV2 name 4=Ch1, 5=SCM, 6=TDS, 7=DO,
8=CON, 9=TUR
Integer Value Setting
0 PPM
1 MG/L
2 mV
PV2Units Integer 24 PV1 units
3 pH
4 NTU
5 %

PV2SetPoint Integer 25 PV2 set point for example 225 = 22.5%

PV2Span Integer 26 PV2 span
PV2Zero Integer 27 PV2 zero
PV2FilterTime Integer 28 PV2 averaging filter time in seconds
PV2DeadBand Integer 29 PV2 set point dead band
PV2Integral Integer 30 PV2 integral (% x 10)
PV2Low Integer 31 PV2 low alarm level
PV2High Integer 32 PV2 high alarm level
PV2LagTimeMode Integer 33 PV2 Lag time mode (0=fixed, 1=slope, 2=point)

PV3 Integer 40 PV3 filtered and scaled

PV3 input selection (0=Modbus, 1=AI1, 2=AI2, 3=AI3,
PV3 Select Integer 41
4=AI4)
PV3SetPoint Integer 42 PV3 set point used when PV3Mode = 3
PV3Span Integer 43 PV3 span
PV3Integral Integer 44 PV3 integral (% x 10)
PV3Mode Integer 45 PV3 Mode (0=Flow, 1=Res, 2=CLC, 3=Feed forward)
PV3LagTimeMode Integer 46 PV3 Lag time mode (0=fixed, 1=slope, 2=point)

PO1DP Integer 60 PO1 decimal position

PO1 Integer 61 PO1 live
PO1Manual Integer 62 PO1 value in manual mode
0 %
PO1Units Integer 63 PO1 units
1 PPD

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 20

 2 GR/H
3 KG/H
4 GPH
5 GPM
6 GPD
7 LPM
8 LPH
PO1Span Integer 64 PO1 Span
1 Cl2
PO1GasType Integer 65 PO1 gas type
0 SO2

b1 PV1 low alarm

b2 PV1 loss alarm
b3 PV2 low alarm
Alarm status b4 PV2 loss alarm
AlarmStatus Integer 66
flag bits b5 PV2 high alarm
B6 PV3 loss alarm
B7 Node 1 comm error
B8 Node 2 comm error
AlarmTime Integer 67 Alarm delay time (secs) – delay time set by user
0 Flow
1 Resl
CtrlMode Integer 68 control mode
2 Compound
3 Feed forward
0 Auto
RunMode Integer 69 run mode
1 Manual
PV1/PV2 0 Maintain Valve
PVxLoss Integer 70
input loss action 1 Close Valve

Table 12. Modbus WQM-100 Water Quality Monitor

Variable Addresses, Register Values, and Features
Name Type Address Description
Hexadecimal Value Float Scale Factor
Flow 0x50 x1
**FlowDP Hex 20 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
Flow Integer 21 Flow live
FlowSpan Integer 22 Flow span
FlowThreshold Integer 23 Flow threshold for PO1Flow
FlowMinCLC Integer 24 Flow min to stop Resl in CLC mode
Percent of FlowSpan below For example
FlowStop Integer 25
which stop 10 = 10% of span
FlowLow Integer 26 Flow low alarm value (0=Off)
Integer Value Setting
0 %
FlowUnits Integer 27
1 GPM
2 MGD

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 21

 3 LPM
4 MLD
5 GPD
6 m /hour
3

Flow dosage value For example

FlowDosage Integer 28
(% x 100) 125 = 1.25%
FlowFilterTime Integer 29 Flow average filter time in seconds

pH live calibrated value For example

Pb1PhInt Integer 30
(pH x 100) 725 = 7.25 pH
For example
Pb1Volts Integer 31 mV live value
535 = 53.5 mV
For example
Pb1CondInt Integer 32 Cond Live Calibrated Value
3035 = 30.35 mS/cm
Integer Value Setting
0 Off
Pb1ProbeType Integer 33 Probe Type 1 pH
2 ORP
3 Conductivity
Pb1FilterTime Integer 34 pH average filter time in seconds
pH low alarm value For example
Pb1Low Integer 35
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
Pb1High Integer 36
(pH x 100) 925 = 9.25 pH

pH live calibrated value For example

Pb2PhInt Integer 40
(pH x 100) 725 = 7.25 pH
41 For example
Pb2Volts Integer mV live value
535 = 53.5 mV
For example
Pb2CondInt Integer 42 Cond Live Calibrated Value
3035 = 30.35 mS/cm
Integer Value Setting
0 Off
Pb2ProbeType Integer 43 Probe Type 1 pH
2 ORP
3 Conductivity
Pb2FilterTime Integer 44 pH average filter time in seconds
pH low alarm value For example
Pb2Low Integer 45
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
Pb2High Integer 46
(pH x 100) 925 = 9.25 pH

pH live calibrated value For example

Pb3PhInt Integer 50
(pH x 100) 725 = 7.25 pH
51 For example
Pb3Volts Integer mV live value
535 = 53.5 mV
For example
Pb3CondInt Integer 52 Cond Live Calibrated Value
3035 = 30.35 mS/cm
Pb3ProbeType Integer 53 Probe Type Integer Value Setting

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 22

 0 Off
1 pH
2 ORP
3 Conductivity
Pb3FilterTime Integer 54 pH average filter time in seconds
pH low alarm value For example
Pb3Low Integer 55
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
Pb3High Integer 56
(pH x 100) 925 = 9.25 pH

pH live calibrated value For example

Pb4PhInt Integer 60
(pH x 100) 725 = 7.25 pH
61 For example
Pb4Volts Integer mV live value
535 = 53.5 mV
For example
Pb4CondInt Integer 62 Cond Live Calibrated Value
3035 = 30.35 mS/cm
Integer Value Setting
0 Off
Pb4ProbeType Integer 63 Probe Type 1 pH
2 ORP
3 Conductivity
Pb4FilterTime Integer 64 pH average filter time in seconds
pH low alarm value For example
Pb4Low Integer 65
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
Pb4High Integer 66
(pH x 100) 925 = 9.25 pH

For example
Temperature
Temp Integer 70 2555 = 255.5K, display
(Kelvin x 10)
still shows C or F
Temp active sensor node
Temp Node Integer 71 1, 2, 3, or 4
number (where to read T)
Integer Value Setting
TempMode Integer 72 Temp mode 0 Auto
1 Manual
Integer Value Setting
TempUnits Integer 73 Temp units 0 C (Celsius)
1 F (Fahrenheit)

PO1 final calibrated

PO1 Integer 90
value
PO1Span Integer 91 PO1 span Full scale value for display
PO1Units Integer 92 PO1 units % etc…
Integer Value Setting
PO1RunMode Integer 93 Run Mode 0 Manual
1 Auto
PO1Manual Integer 94 Manual Value User adjustable

PIDCtrlMode Integer 95 PID Control mode Integer Value Setting

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 23

 0 Off
1 Flow
2 Set Point
Compound
3
Loop
PID set point based
PIDChannel Integer 96 Select 1, 2, 3, or 4
on which channel
PIDSetPoint Integer 97 PID Set Point User selected value
PIDDeadBand Integer 98 PID Dead Band User selected value
PIDIntegral Integer 99 PID Integral Value Ex. 200 = 20.0 %

AO1Mode Integer 100 AO1 Mode

AO2Mode Integer 101 AO2 Mode 0=PO1, 1=Probe 1, 2=Probe 2,
AO3Mode Integer 102 AO3 Mode 3=Probe 3, 4=Probe 4, 5=Temp
AO4Mode Integer 103 AO4 Mode

b0:DataLogAlm, b1:Pb1LowAlm,
b2:Pb1HighAlm, b3:Pb2LowAlm,
b4:Pb2HighAlm,
AlarmStatus Integer 104 Alarm Status b5:Pb3LowAlm,b6:Pb3HighAlm,
b7:Pb4LowAlm,b8:Pb4HighAlm,
b9:TempAlm, b10:FlowLowAlm,
b11:FlowLossAlm, b12:ComError

AlarmMode Integer 105 Alarm Mode 0=nonlatching, 1 = latching

Relay1Mode Integer 110 Relay 1 mode 0=Ch1 Low, 1=Ch1 High, 2=Ch2 Low,
Relay2Mode Integer 111 Relay 2 mode 3=Ch2 High, 4=Ch3 Low, 5=Ch3 High,
Relay3Mode Integer 112 Relay 3 mode 6=Ch4 Low, 7=Ch4 High, 8=Flow Low,
9=Any Alarm
Relay4Mode Integer 113 Relay 4 mode
Relay1 Integer 114 Relay 1 State
Relay2 Integer 115 Relay 2 State
0 = OFF, 1 = ON
Relay3 Integer 116 Relay 3 State
Relay4 Integer 117 Relay 4 State

Table 13. Modbus RPH-260 Residual Analyzer

Variable Addresses, Register Values, and Features
Name Type Address Description
Res1DP Integer 10 Resl 1 decimal position
Res1 Integer 11 Resl 1 final calibrated value
Res1Low Integer 12 Resl 1 low alarm value (0=off)
Resl1High Integer 13 Resl 1 High Alarm value
Resl1FlowStopEnb Integer 14 Resl 1 sample water flow stop alarm enable
Res1Span Integer 15 Resl 1 span
Resl1Units Integer 16 Resl 1 engineering units (0=PPM, 1=mg/l)
Resl1FilterTime Integer 17 Resl 1 Avg filter time (seconds)
Resl1ProbeType Integer 18 Resl 1 probe type (0=off, 1=F1, 2=F2, 3=T1, 4=F3)
Resl1pHProbe Integer 19 Resl 1 pH probe used for compensation (1 or 2)

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 24

 Resl1FlowStop Integer 92 Resl 1 sample water flow (0=ok, 1=stopped)

Res2DP Integer 20 Resl 2 decimal position

Res2 Integer 21 Resl 2 final calibrated value
Res2Low Integer 22 Resl 2 low alarm value (0=off)
Resl2High Integer 23 Resl 2 High Alarm value
Resl2FlowStopEnb Integer 24 Resl 2 sample water flow stop alarm enable
Res2Span Integer 25 Resl 2 span
Resl2Units Integer 26 Resl 2 engineering units (0=PPM, 1=mg/l)
Resl2FilterTime Integer 27 Resl 2 Avg filter time (seconds)
Resl2ProbeType Integer 28 Resl 2 probe type (0=off, 1=F1, 2=F2, 3=T1, 4=F3)
Resl2pHProbe Integer 29 Resl 2 pH probe used for compensation (1 or 2)
Resl2FlowStop Integer 93 Resl 2 sample water flow (0=ok, 1=stopped)

pH 1 live calibrated value For example

Ph1PhInt Integer 30
(pH x 100) 725 = 7.25 pH
Integer Value Setting
0 Off
Ph1ProbeType Integer 31 Probe 1 Type 1 pH
2 ORP

0=off, 1=auto,
pH1CompMode Integer 32 pH 1 Comp mode
2=manual
PH1FilterTime Integer 33 pH 1 average filter time in seconds
pH1Manual Integer 34 pH 1 manual value
pH1Low Integer 35 pH 1 low alarm value
pH1High Integer 36 pH 1 High Alarm Value

pH 2 live calibrated value For example

Ph2PhInt Integer 40
(pH x 100) 725 = 7.25 pH
Integer Value Setting
0 Off
Ph2ProbeType Integer 41 Probe 2 Type 1 pH
2 ORP

0=off, 1=auto,
pH2CompMode Integer 42 pH 2 Comp mode
2=manual
PH2FilterTime Integer 43 pH 2 average filter time in seconds
pH2Manual Integer 44 pH 2 manual value
pH2Low Integer 45 pH 2 low alarm value
pH2High Integer 46 pH 2 High Alarm Value

For example
Temperature 1
Temp1Show Integer 50 2555 = 255.5K, display
(Kelvin x 10)
still shows C or F
Integer Value Setting
0 Off
Temp1Mode Integer 51 Temp 1 mode
1 Auto
2 Manual
Temp1Units Integer 52 Temp 1 units Integer Value Setting

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 25

 0 C (Celsius)
1 F (Fahrenheit)

For example
Temperature 2
Temp2Show Integer 53 2555 = 255.5K, display
(Kelvin x 10)
still shows C or F
Integer Value Setting
0 Off
Temp2Mode Integer 54 Temp 2 mode
1 Auto
2 Manual
Integer Value Setting
Temp2Units Integer 55 Temp 2 units 0 C (Celsius)
1 F (Fahrenheit)

AO1Mode Integer 60 AO1 Mode 0=Res1, 1=Res2, 2=pH/ORP1,

AO2Mode Integer 61 AO2 Mode 3=pH/ORP2, 4=Temp1,
AO3Mode Integer 62 AO3 Mode 5=Temp2, 6=Cond, 7=Press,
AO4Mode Integer 63 AO4 Mode 8=PO1, 9=PO2

alarm status flag bits (b0:DataLogAlm, b1:Res1LowAlm,

b2:Res1HighAlm, b3:Res1LossAlm, b4:Res2LowAlm,
b5:Res2HighAlm, b6:Res2LossAlm, b7:pH1LowAlm,
b8:pH1HighAlm, b9:pH2LowAlm, b10:pH2HighAlm,
b11:Temp1Alm, b12:Temp2Alm,
AlarmStatus Integer 70
b13:Res1FlowStopAlm, b14:Res2FlowStopAlm,
b15:CondHighAlm,
b16:CondLowAlm, b17:PressHighAlm,
b18:PressLowAlm, b19:PressLossAlm,
b20:ComErrorAlm)
AlarmMode Integer 71 Alarm Mode 0=nonlatching, 1 = latching
AlarmTime Integer 72 Alarm Delay Time seconds

Relay1Mode Integer 80 Relay 1 mode 0=Res 1 Low Alm, 1=Res 1 High Alm,
2=Res 2 Low Alm, 3=Res 2 High Alm,
Relay2Mode Integer 81 Relay 2 mode 4=pH/ORP 1 Alarm,
Relay3Mode Integer 82 Relay 3 mode 5=pH/ORP 2 Alarm, 6=Any Alarm,
7=Flow 1 Stop Alarm, 8=Flow 2 Stop
Alarm, 9=Cond Low Alm,
Relay4Mode Integer 83 Relay 4 mode 10=Cond High Alm, 11=Press Low Alm,
12=Press High Alm
Relay1 Integer 84 Relay 1 State
Relay2 Integer 85 Relay 2 State
0 = OFF, 1 = ON
Relay3 Integer 86 Relay 3 State
Relay4 Integer 87 Relay 4 State

DataLogEnb Integer 90 Data Log Enable 0=off, 1=enable

Data Log Time
DataLogTime Integer 91 Seconds
Interval

CondEnb Integer 100 Conductivity Enable

Cond Integer 101 Conductivity Live (mS x 100, ex. 125 = 1.25mS)
CondLow Integer 102 Conductivity Low alarm value
CondHigh Integer 103 Conductivity high alarm value

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 26

 PressEnb Integer 110 Pressure enable
Press Integer 111 Pressure live (0x30 = psi, 0x21=bar)
PressMa Integer 112 Pressure live (mA x 100, ex. 425 = 4.25mA)
PressSpan Integer 113 Pressure Span
PressLow Integer 114 Pressure low alarm value
PressHigh Integer 115 Pressure high alarm value
PressUnits Integer 116 Pressure units (0=psi, 1=bar)
FlowDP Integer 120 Flow decimal position
Flow Integer 121 Flow Live
Flow Span Integer 122 Flow Span
Flow Threshold Integer 123 Flow threshold for PO1Flow
FlowMinCLC Integer 124 Flow min to stop the Resl in CLC mode
FlowStop Integer 125 Flow percent of FlowSpan below which stop
Flow Low Integer 126 Flow low alarm value (0=off)
Integer Flow engineering units (0=%, 1=GPM, 2=MGD,
Flow Units 127
3=LPM, 4=MLD, 5=GPD, 6=M3/H)
Flow Dosage Integer 128 Flow dosage value (%)
Flow Filter Time Integer 129 Flow filter time (seconds)

PID1CtrlMode Integer 130 PID1 Ctrl mode (0=Off, 1=Flow, 2=SP, 3=Compound)
PID1Channel Integer 131 PID1 Channel (0=Residual, 1=pH1, 2=ORP1, 3=Cond)
PID1SetPOint Integer 132 PID1 set point (Res or pH or ORP or Cond)
PID1DeadBand Integer 133 PID1 dead band (Res, pH, ORP, or Cond)
PID1 Integral Integer 134 PID1 integral value (%)

PID2CtrlMode Integer 135 PID2 Ctrl mode (0=Off, 1=Flow, 2=SP, 3=Compound)
PID2Channel Integer 136 PID2 Channel (0=Residual, 1=pH1, 2=ORP1, 3=Cond)
PID2SetPOint Integer 137 PID2 set point (Res or pH or ORP or Cond)
PID2DeadBand Integer 138 PID2 dead band (Res, pH, ORP, or Cond)
PID2 Integral Integer 139 PID2 integral value (%)

PO1 Integral 140 PO1 final calibrated value

PO1Span Integral 141 PO1 span
Integral PO1 engineering units (0=%, 1=PPD, 2= GR/h,
PO1Units 142
3=KG/H, 4=GPH, 5=GPM, 6=GPD)
PO1Run Mode Integral 143 PO1 run mode (1=Auto, 2=Manual)
PO1Manual Integral 144 PO1 Manual value

PO2 Integral 150 PO2 final calibrated value

PO2Span Integral 151 PO2 span
Integral PO2 engineering units (0=%, 1=PPD, 2= GR/h,
PO2Units 152
3=KG/H, 4=GPH, 5=GPM, 6=GPD)
PO2Run Mode Integral 153 PO2 run mode (1=Auto, 2=Manual)
PO2Manual Integral 154 PO2 Manual value

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 27

 Table 14. Modbus RAH-280 Residual Analyzer
Variable Addresses, Register Values, and Features
Name Type Address Description
Hexadecimal Value Float Scale Factor
Flow 0x50 x1
**FlowDP Hex 20 decimal 0x31 x 10
position 0x22 x 100
0x13 x 1000
Flow Integer 21 Flow live
FlowSpan Integer 22 Flow span
FlowThreshold Integer 23 Flow threshold for PO1Flow
FlowMinCLC Integer 24 Flow min to stop Resl in CLC mode
Percent of FlowSpan below For example
FlowStop Integer 25
which stop 10 = 10% of span
FlowLow Integer 26 Flow low alarm value (0=Off)
Integer Value Setting
0 %
1 GPM
2 MGD
FlowUnits Integer 27
3 LPM
4 MLD
5 GPD
6 m3/hour
Flow dosage value For example
FlowDosage Integer 28
(% x 100) 125 = 1.25%
FlowFilterTime Integer 29 Flow average filter time in seconds

ReslDP Integer 30 Resl decimal position

Resl Integer 31 Resl final calibrated value
ReslLow Integer 32 Resl low alarm value (0=off)
ReslHigh Integer 33 Resl high alarm value (0=off)
ReslFlowStop Integer 34 Resl sample water flow (0=ok, 1=stopped)
ReslSpan Integer 35 Resl span
ReslUnits Integer 36 Resl engineering units (0=PPM, 1=MG/L)
ReslFilterTime Integer 37 Resl filter time (seconds)

pH live calibrated value For example

PhInt Integer 40
(pH x 100) 725 = 7.25 pH
PhMode Integer 41 pH mode (0=off, 1=auto, 2=manual, 3=monitor)
pHFilterTime Integer 42 pH average filter time in seconds
pHManual Integer 43 Manual value
pH low alarm value For example
Pb1Low Integer 44
(pH x 100) 425 = 4.25 pH
pH high alarm value For example
Pb1High Integer 45
(pH x 100) 925 = 9.25 pH

OrpEnb Integer 50 ORP enable

51
ORPVolts Integer ORP live value (mV)

Hydro Instruments Modbus Manual Rev 2022/09/16 Page 28

ORPFilterTime Integer 52 ORP filter time working seconds
ORPLow Integer 53 ORP Low Alarm Value
ORPHigh Integer 54 ORP High Alarm Value

CondEnb Integer 60 Conductivity enable

61
COndInt Integer Conductivity live calibrated value in mS
CondLow Integer 63 Conductivity Low Alarm Value
CondHigh Integer 64 Conductivity High Alarm Value

For example
Temperature
Temp Integer 70 2555 = 255.5K, display
(Kelvin x 10)
still shows C or F
Temp active sensor node
Temp Node Integer 71 1, 2, 3, or 4
number (where to read T)
Integer Value Setting
TempMode Integer 72 Temp mode 0 Auto
1 Manual
Integer Value Setting
TempUnits Integer 73 Temp units 0 C (Celsius)
1 F (Fahrenheit)

PO1 final calibrated

PO1 Integer 90
value
PO1Span Integer 91 PO1 span Full scale value for display
PO1Units Integer 92 PO1 units % etc…
Integer Value Setting
PO1RunMode Integer 93 Run Mode 0 Manual
1 Auto
PO1Manual Integer 94 Manual Value User adjustable

Integer Value Setting

0 Off
PIDCtrlMode Integer 95 PID Control mode 1 Flow
2 Set Point
3 Compound
PID set point based
PIDChannel Integer 96 Select 1, 2, 3, or 4
on which channel
PIDSetPoint Integer 97 PID Set Point User selected value
PIDDeadBand Integer 98 PID Dead Band User selected value
PIDIntegral Integer 99 PID Integral Value Ex. 200 = 20.0 %

AO1Mode Integer 100 AO1 Mode

AO2Mode Integer 101 AO2 Mode 0=PO1, 1=Resl, 2=pH, 3=ORP,
AO3Mode Integer 102 AO3 Mode 4=Cond, 5=Temp
AO4Mode Integer 103 AO4 Mode

b0:DataLogAlm, b1:ReslLowAlm,
b2:ReslHighAlm, b3:PHLowAlm,
AlarmStatus Integer 104 Alarm Status
b4:PHHighAlm,
b5:ORPLowAlm,b6:ORPHighAlm,

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 b7:CondLowAlm,b8:CondHighAlm,
b9:FlowLowalm,
b10:FlowLossAlm, b11:TempAlm,
b12:FlowStopAlm, b13:ComError

AlarmMode Integer 105 Alarm Mode 0=nonlatching, 1 = latching

Relay1Mode Integer 110 Relay 1 mode 0=Ch1 Low, 1=Ch1 High, 2=Ch2 Low,
Relay2Mode Integer 111 Relay 2 mode 3=Ch2 High, 4=Ch3 Low, 5=Ch3 High,
Relay3Mode Integer 112 Relay 3 mode 6=Ch4 Low, 7=Ch4 High, 8=Flow Low,
9=Any Alarm
Relay4Mode Integer 113 Relay 4 mode
Relay1 Integer 114 Relay 1 State
Relay2 Integer 115 Relay 2 State
0 = OFF, 1 = ON
Relay3 Integer 116 Relay 3 State
Relay4 Integer 117 Relay 4 State

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VI. Troubleshooting

Consider the following points if having difficulty establishing communication:

1.) The master can request several addresses in one packet request, but the addresses have to be
sequential.

2.) When the master requests data the slave node may not respond instantly because its running
the program loop.
a. The SCADA has a parameter that can be set which is how long to wait for a response.
b. Another parameter is the polling interval- how often does the SCADA request data. If its
too fast the slave node may not be ready.
c. You could try to increase those times and also only request 1 address in the packet from
one of the addresses which is not working to see if the address can be read properly.

3.) Another issue is that there is very specific timing required for Modbus regarding the data packet
and the interval timing between packets which nodes on the network use to determine when a
packet ends and when a new packet begins.
a. Windows and Linux are not real time operating systems. So there is no way to ensure
this timing in a Windows or Linux application program.
b. The solution is the interface hardware between the computer and the RS-485 network
must handle this timing.
c. Good SCADA software accounts for this. Keep this in mind.

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