YOKOGAWA DO71 User manual

Technical Optical Dissolved Oxygen, model DO71/DO72

Information MODBUS Communication

TI 12J06J01-00EN-P

Yokogawa Process Analyzers Europe B.V. TI 12J06J01-00EN-P, 1st Edition

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MODBUS Communication - Contents 3 
 
All Rights Reserved. Copyright © 2022, Yokogawa Process Analyzers Europe B.V. TI 12J06J01-00EN-P 
 
Contents 
 
Introduction....................................................................................................................................4 
General ....................................................................................................................................5 
1 MODBUS setup ...............................................................................................................5 
2 Function code / Exception code ...................................................................................5 
3 MODBUS communication..............................................................................................6 
4 Connection......................................................................................................................6 
MODBUS map.........................................................................................................................8 
1 Hold Register DO............................................................................................................9 
Failures and Warnings DO..................................................................................................17 
Low/High Point Calibration DO...........................................................................................18 
Revision History...................................................................................................................19 
 

MODBUS Communication - Introduction 4

Introduction

This document describes MODBUS communicationby the Optical Dissolved Oxygen (DO) sensor,

model DO71 and DO72, for a basic user.

Before communication using the MODBUS protocol, refer to the User’s Manual of the Optical

Dissolved Oxygen sensors, model DO71 and model DO72 (IM 12J06J01-00EN-P) for details of

the parameters and connections.

Latest revision of the User’s Manual can be downloaded from the website:

https://www.yokogawa.com/solutions/products-platforms/process-analyzers/liquid-

analyzers/#Downloads

You can use the QR-code for quick-access.

NOTE

No part of the Technical Information may be transferred or reproduced without prior written

consent from YOKOGAWA.

YOKOGAWA reserves the right to make improvements in the Technical Information and product

at any time, without notice or obligation.

MODBUS Communication –General 5

1. General

Optical Dissolved Oxygen sensors are slave devices which can be configured or are sending

process data using Bi-directional digital communication (RS485, half-duplex) with full MODBUS

(RTU) support. The power for the Optical Dissolved Oxygen sensors must be supplied by a HOST

or by a separate power supply in the range +7VDC up to +30VDC. Maximum power of the Optical

Dissolved Oxygen sensors is 1W in active mode, and 150mW in stand-by mode.

1.1 MODBUS setup

The following list shows the required setting by HOST to establish communication between the

HOST as master device and the Optical Dissolved Oxygen sensor as slave device. The procedure

for changing list items is explained in the following chapters in this document.

Slave address : 1

Serial Profile : 19200 bps, 8 data bits, No parity, 2 stop bits

NOTE

Slave address and Serial Profile are configurable as explained in this document.

IncaseofusingmultipleOpticalDissolvedOxygensensorsinabussystem,connectedtooneHOST,

the Slave addresses of all the Optical Dissolved Oxygen sensors must be unique. Because initial

settingofaddressis1itisrecommendedtochangetheinitial addressvaluetopreventcommunication

conflicts in case a new purchased Optical Dissolved Oxygen sensor is added to the bus.

Serial profile of the slave device(s) mustbe the same as the HOST.

1.2 Function code / Exception code

MODBUS Function codes used for DO71 and DO72:

Function

Function code (hex)

Read Hold Register

Write Single Register

Write Multiple Registers

Exception codes used for DO71 and DO72:

Name

Exception code

Meaning

Illegal Function

0x01

The Function code received is not an

allowable action for the slave

Illegal Data Address

0x02

The Data Address received is not an

allowable address for the slave

MODBUS Communication –General 6

1.3 MODBUS communication

If the Optical Dissolved Oxygen sensor is used with a HOST, the following must be considered.

⚫MODBUS response timing

TheOpticalDissolvedOxygensensor’s HR (HOLDRegister)responsetoaHOSTHR Readrequest

is within 100ms. The timing in between a response and a new request must be at least 10ms.

Figure 1.3: Timing diagram

⚫HOLD Register renewal cycle

Process value sent in HOLD Register is configurable, initial value is 1 s.

1.4 Connection

⚫BUS system

Wired connection:

Figure 1.4: DO71 sensor with HOST

< 100 ms > 10 ms

HOST HR: Hold Register

DO sensor

HR Request

HR Response

HR Request

MODBUS Communication –General 7

Table 1.4.1: DO71 connection definition

Terminal

pin no.

(Fixed cable)

Wire

colour

Description

yellow

RS485 Data + (B)

green

RS484 Data –(A)

white

Power - GND

brown

Power - VDC

transparent

Cable shield / Probe body

Table 1.4.2: DO72 connection definition

Terminal

pin no.

(WU10-V-D-xx)

Wire

colour

Connector pin

(Variopin)

Description

green

RS485 Data + (B)

yellow

RS484 Data –(A)

white-shield

Power - GND

white-core

Power - VDC

black

Shield

Cable shield /

Probe body

xx: Cable length in meters

MODBUS Communication –MODBUS map 8

2. MODBUS map

Data type for Optical Dissolved Oxygen sensor MODBUS map:

Data type

Definition

Float

floating point (4byte, little endian byte swap [CDAB])

IEEE754

NaN: 0x7FFFFFFF

Uint32

32 bit unsigned integer, little endian byte swap [CDAB]

ASCII

character set (using one byte per character), multiple registration possible,

little endian byte swap [CDAB])

Access (load/import) to multiple data types, such as Float, Uint32, ASCII etc., must be

implemented at once. The current version does not support Script yet.

Access

Function

Function Code (hex)

Data Access

16 bits

Read Hold Registers

Write Single Register

Write Multiple Register

Hold Registers are Read only (R) or Read/Write (R/W).

NOTE

The content of this Modbus Map is based upon DO71 firmware YPA 1.4.0.xx and DO72 firmware

YPA 1.4.0.xx

MODBUS Communication –Hold Register DO 9

2.1 Hold Register DO

If applicable, in the Value/description field the Factory Default setting (D), Low limit setting (L) and

High limit setting (H) are explained. NaN does mean that there is Not a Number defined.

NOTE

Because no limit checks are implemented, incorrect settings or settings outside the specified range

are accepted as is. Pleasetake care that settings aredone correctly and within the specified range.

Address

Item name

Data type

Access

Value / description

1031

Firmware version

ASCII

Alphanumeric Firmware version code:

16 bytes, 8 addresses

2089

Oxygen unit

Uint32

R/W

0x 0000 0010 % vol O2

0x 0000 0020 % air saturation

0x 0000 0040 ppb (µg/L) 2)

0x 0000 0080 ppm (mg/L) 2)

0x 0400 0000 µmol/L 2)

0x 0800 0000 % DO saturation

0x 2000 0000 hPa (mbar)

0x 4000 0000 ppm gas 1) 2)

0x 8000 0000 Torr

Remark:

1) ppm gas only possible with DO72-T

2) Setting not possible in

measurement mode “Dry”

(register HR5703)

D: % DO saturation

2091

Oxygen value

Float

Calculated oxygen value in oxygen unit

as defined in register HR2089

Remark:

1) The calculated oxygen value is only

updated if an interval rate is set

(register HR3499)

2) When value is -999 this means

there is no calculated output

2093

Error

Uint32

For details see Section 3.1

2409

Temperature Unit

Uint32

R/W

0x 0000 0002 K

0x 0000 0004 °C

0x 0000 0008 °F

D: °C

2411

Temperature Value

Float

Measured temperature value used for

temperature compensation

MODBUS Communication –Hold Register DO 10

Address

Item name

Data type

Access

Value / description

3115

Salinity

Float

R/W

Salinity value used for salinity

compensation (unit is g/L)

D: 0

3145

Pressure Comp. Unit

Uint32

0x 0080 0000 hPa (mbar)

Remark:

1) This is a fixed unit

D: hPa (mbar)

3147

Volatile Pressure Comp. Value

Float

R/W

Pressure value in hPa (mbar) used for

oxygen calculation

Remark:

1) If included in a multi register write,

no change will take place

2) Value is not written into Flash

memory

D: By default, this is the Persistent

Pressure Comp. value (register

HR3153)

3153

Persistent Pressure Comp. Value

Float

R/W

Default setting for compensation

pressure value in hPa (mbar)

Remark:

1) Do not use this register frequently

due to limited number of write

cycles into Flash memory. For

frequent pressure changes please

use register HR3147

2) Value is stored into Flash memory

and restored at startup

D: Set by manual input

3497

Interval Unit

Uint32

R/W

0x 0000 0001 seconds

Remark:

1) This is the time unit for the oxygen

measurement interval rate, fixed

set to seconds

D: seconds

3499

Interval rate

Uint32

R/W

Oxygen measurement interval rate in

time unit as set in register HR3497

Remark:

1) Setting the interval rate to 0

deactivates the continuous

measurement

(see register HR9000)

D: 1

L: 0

H: 300

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