modbus connection of AC800M controller to AC110 and about 7s delay in receive and send signals

Hello,

In our project,I have connected one contrller AC800M through CI853 to the 2 AC110 controller using modbus RTU by using westermo modem MD-12.I have configured both side and communication is ok ,but I have about 7s delay in signal updating in both side.I have attached my modbus logic and hardware setting.Please help me how can I fix this delay time problem.

thanks a lot.

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takabi Rank: 262

Asked 2 years ago

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7 Seconds does seem far too long. I think that your Program design is making it hard to see if you are getting tiemouts or if you are overloading the CI853 with too many read requests. Some small changes may make it easier to debug.

Your poll time is too short, move it out to 10 or 15 seconds. With a poll this short you're continually polling while you're also trying to send messages.

Your timeout is also probably too short. At 2 seconds this isbarely longer than the 1 second sending interval. If you are having timeout problems then you wont see them before you just resend the message with the regular clock pulse cycle time.

IMHO, The FTrig at TP blocks are not required. Remove them and also the En_N1 and En_N2 variables. Move the Pulse Generator AFTER the MBConnect and enable the generator if "Valid AND NOT Error". Use separate pulse generators for each port.

Connect the output of the Pulse Generator to the REQ of the MBReads ONLY if your AC110 immediately responds withing the 1 second pulse time. Otherwise, You need to slow your pulse generator or chain the NRd teminals of each MBRead to enable the Next read only after the previous read has completed.

And obviously if the PLC interfaces are identical then simply write the entire program in a Library or user defined function block and instantiate it twice instead of Copy/Pasting it.

The task interval for your program should be 500Ms or shorter. I would suggest 250 or 125mSec so that your MBRead blocks have several opportunities to be updated before the next set of MBRead requests are generated.

The CI853 is actually quite good at queing up multiple Read requests as long as you dont overload the response time of the Slave PLC.

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by takabi Rank: 262 on 10/21/2015 1:14:28 AM | Like (0) | Report

Dear Rob
Thank you for your kind attention.Is it possible to make Polling time to Zero or not?
For your information In modbus network the CI853 is master and there are two Nodes (AC110)with address 2,3 in network,then I have to read and write them, is it necessary to make chain all read and write in both nodes toghether?and how we can chain them?

thanks a lot.

by Rob Lyon AKS expert

Rank: 2 on 10/21/2015 8:43:24 AM | Like (0) | Report

Are the two slaves on the same multidrop or on 2 different ports of the CI853 ?I would strongly recommend that you use 2 separate ports otherwise if one PLC fails the other PLC interface will have to wait for the failed PLC to timeout on EVERY message making your link very slow.

If the PLCs are on different ports then obviously no, don't chain the reads for both PLCs together. The Ndr output of the read block goes to the Req of the next read.

If the PLCs respond quickly and the amount of data is small then it is not necessary to chain the Read Requests like this. Typically I don't bother.

by takabi Rank: 262 on 10/21/2015 9:53:33 AM | Like (0) | Report

Dear Rob
Both PLC are on the same ports and we have multidrop on one port.Then I have to read and write two nodes in multiplexing method.I think it is better to send a request to the first Read function in node1 and connect Ndr of first block to req terminal of next read or next write and do it like this from node 1 to node2 and at least return to first function.Is it correct or not?
Another problem is that in MVB database of AC110 Valid terminal is toggling between 0,1 when Cycletime parameter terminal in MVB is less than 32.It means updating between PC program and MVB is too long.Can be this cause of our link slow?

thank you very much

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Rob Lyon

Rank: 2

Answered 2 years ago

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modbus connection of AC800M controller to AC110 and about 7s delay in receive and send signals

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