Modbus tcp communication fault finding

asked 2021-05-14 08:12:07 +0000

MGharat
1 ●1

I have Mobus TCP network communicating one PLC client & 18 nos of Feeders as servers. But sometimes any of server IP shows fault condition at PLC software after 1/2 secs fault disappears automatically & communication error is resolved. But when we taken wireshark trace through analyzer , we do not get any timeout/error in communication when actaully fault occurs at PLC. can u guide ?

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answered 2021-05-14 10:02:41 +0000

grahamb

flag of United Kingdom of Great Britain and Northern Ireland

23835 ●4 ●973 ●227 https://www.wireshark.org

Often the client software has some configuration option to set a timeout for the expected response, a bit of historical baggage from serial links. When using TCP there is no need for this (or the often associated config. value of "retries") as the TCP stack will either deliver a response (possibly after TCP retransmissions) or will indicate a failure of the stream.

If there is a comms. or message timeout, try increasing it a bit (or even disable it if an option). Similarly set any retries option to 0.

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answered 2021-05-14 08:40:03 +0000

hugo.vanderkooij
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It depends where you do the actual measurements. I would prefer to do measurements on both ends and also compare it with network statistics. But if you don't see any obvious network issue it could very well be a software glitch.

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what you mean by - measurements on both ends ? can you give some more idea ?

MGharat ( 2021-05-14 08:51:37 +0000 )edit

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