Owner's manual
Table Of Contents
- DMT345/346 USER'S GUIDE
- TABLE OF CONTENTS
- GENERAL INFORMATION
- PRODUCT OVERVIEW
- INSTALLATION
- OPERATION
- Getting Started
- Display/Keypad
- MI70 Link Program for Data Handling
- Serial Line Communication
- LAN Communication
- Communicating with a Transmitter in POLL Mode
- General Settings
- Serial Output Settings
- Data Recording
- Analog Output Settings
- Operation of Relays
- Sensor Functions
- MODBUS
- MAINTENANCE
- CALIBRATION AND ADJUSTMENT
- TECHNICAL DATA
- EXAMPLE INSTALLATION OF DMT346
- CALCULATION FORMULAS
- MODBUS REFERENCE
Chapter 5 ___________________________________________________________________ Modbus
VAISALA _______________________________________________________________________ 137
CHAPTER 5
MODBUS
This chapter contains information that is needed when operating the
transmitter using the Modbus protocol.
Overview of Modbus Protocol Support
The DMT345/346 transmitters can be accessed using the Modbus serial
communication protocol. Support for Modbus protocol is available on all
DMT345/346 transmitters as a standard feature from software version
5.10 onward. The supported Modbus variants and the connections they
use are listed in Table 32 below.
Table 32 Supported Modbus Variants
Supported Modbus Variant
Connections
Modbus RTU (Serial Modbus)
RS-232 (standard User Port)
RS-422/485 interface (optional module)
Modbus TCP (Ethernet Modbus)
LAN interface (optional module)
WLAN interface (optional module)
The supported Modbus functions, registers, configuration options, and
diagnostics are described in Appendix C, Modbus Reference, on page
177.
Note the following limitations of the Modbus implementation:
- Modbus TCP mode accepts only one TCP connection at a time.
Design the system so that only one Modbus TCP client accesses the
transmitter.
- Modbus TCP can process reliably only one Modbus transaction at a
time. Reduce the polling rate of the client to avoid nested transactions.