Emerson Exchange 365

Troubleshoot and configure Modbus

In need of some assistance on where to start for navigating to either reconfigure modbus device communication (if need to replaced) or troubleshoot existing. Any help would be appreciated, therefore in the midst of getting familiar with delta v. 

gbilly

• 2 May 2024 2:29 PM
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2 Replies

• Andre Dicaire

  

  • 3 May 2024 4:07 PM

  Not much information to go on. Modbus implies serial communications, with RS232 or RS485 multidrop. Things like baud rate, stop bit, parity need to be aligned with the client and server nodes. there is also the device addressing to set up. Also understanding the data format of the Holding and input registers of the device with respect to byte and word order. And finally the actual mapping.
  
  So it starts by knowing how the data is mapped into the registers and the communication details, and aligning the client to establish the connection with the right settings and read the data. On the DeltaV side, which serial card do you have? There are some configuration options on the programmable card to align byte and word order if needed. The addressing, communication settings and physcial media are configured to match.
  
  If you meant Modbus TCP, the communication layer is ethernet, typically auto negotiated. Could be using a VIM or native via EIOC or PK controller.
  
  And what is the problem you are trying to trouble shoot. Hardest thing to uncover is which side of the connection is the problem. Setting up a working server with the client allows you to confirm the Client is good. Then bring on the device in question. With Serial cards, they can be configured as a client or a server, allowing you to use one as a "known" client and work out the various settings.
  
  Documentation is the key.

  Andre Dicaire

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• gbilly

  

  • 3 May 2024 4:53 PM

  In reply to Andre Dicaire:

  Yes sir, I appreciate your assistance upon request. Well I have a Otis instruments Gen 2 H2S Gas Detectors that has bad mod alarm, for radio box it's 2 wire to serial to RS485 connected to MTL800 plc with Node service monitor to LAN B ethernet to delta V switch. Looks like modbus is through PK Controller, I wish this reply forum to upload pics, or when I try it ends up being too large to send to be more pacific on the setup.

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