SCADA running slow on Modbus TCP IP protocol.


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Hello Sir/Madam,

The SCADA project has 4 PLC's  connected on Modbus TCP communication protocol. However, if any device is switched off the project file runs too slow. Is there a need that all 4 devices must be power on. Is there any suggestion that if no device is connected or any one or more device are  connected the SCADA doesn't run slow. A trial of device bypass using sequence has not much success as the project file is closed on its own without any error. Is it possible that there is a log of the file being shutdown?.

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If you have multiple PLC's that are on different IP addresses and not on a single RS485 chain, you can simply give all the channels of each PLC a different Timing/Offset combination.  This will cause DAQFactory to query them simultaneously, and timeouts caused by one PLC being offline won't affect the others.  So, for example, PLC1 might have its channels on Timing 1, Offset 0, while PLC2 might have Timing 1, Offset 0.25, and PLC3 might have Timing 1, Offset 0.5.

As for device bypass, it is likely that you created circular logic and blew the stack.  I'd have to see your document to truly tell.  

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Thank you for the response.

So, After giving the channels of each PLC a different Timing/Offset combination will solve the issue of lagging of data if any one more  PLC is not powered up?. 

I will share the document for sure by the end of week.

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