Modbus communication problem between S7 300 and Honeywell DCS.

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Thread Starter

SULFIKER

I conected my siemens PLC as a slave (CPU313C-2DP with CP341) with Honeywell DCS as master. Communication parameters as follows:

Digital tags: 100 Nos. (only read)
Analog Tags: 32 Nos. (only read)
Baud rate: 9600 kbps
Distance: 250 meters

Honeywell DCS side they are using Quick Builder Software for configuring Modbus tags.

All the digitals tags are communicating very well.

But some of the Analog datas are failing randomly. Some times all the datas are communicating well. After seeing the problem the scanning time of some of the tags they incresed in DCS side, after that the number failing tags are redused.But still we are facing problem. Please forward me some tips to solve this problem.

with regards,
sulfiker
 
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Shahid Waqas

It would help if you can tell the model of the honeywell DCS. If you are connecting using the EPLCG or PLCG (TDC3000 / TPS), then the scanning time is a problem. Increasing the scan time should solve the problem.

I have faced this problem when communicating with other sub-systems to the (E)PLCGs.
 
Ensure the modbus addresses are serial i.e 1,2,3 etc. If some adresses are at a gap then such problem may arise. some other hints are - reduce the scan time of the points built.
 
What is the brand of terminal server installed. I faced issue on a plant where moxa terminal servers were installed and were facing huge delays in communication. Honeywell tech support recommended to replace them with Systech terminal servers which resolved the issue.
 
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