Vaisala Optimus OPT100 - Modbus Registers Overview

A complete 32-bit floating point or 32-bit integer value should be read and written in a single
Modbus transaction.
Reading the measurement data registers with incorrect floating
point format setting may occasionally result in correct-looking, but nevertheless
incorrect values.
CAUTION!
It is highly recommended to verify that you have configured the floating point
format correctly on your Modbus host system by reading a floating point value
from a test value register.
A.4 Modbus registers
Registers are numbered in decimal, starting from 1. Register addresses in actual Modbus
messages (Modbus Protocol Data Unit (PDU)) are in hexadecimal and start from zero. Register
number 1 corresponds to address 0
hex
in the actual Modbus message.
Reading the wrong register(s) may result in correct-looking values.
Check the reference documentation of your Modbus host (PLC) to verify which
notation it uses for Modbus register addresses.
CAUTION!
A.4.1 Measurement data registers
Table 28 Measurement data registers (read-only)
Register number Address Register
description
Data format Unit and notes
Present values
21 0014
hex
Methane 32-bit float ppm
v
0015
hex
23 0016
hex
Acetylene 32-bit float ppm
v
0017
hex
25 0018
hex
Ethylene 32-bit float ppm
v
0019
hex
27 001A
hex
Ethane 32-bit float ppm
v
001B
hex
Appendix A – Modbus reference
105