ABB OPC Server - write ok, read fails

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2010-12-24
2013-05-30
  • Markus Clarkus
    Markus Clarkus
    2010-12-24

    Hi, 

    Has anyone tried the ABB OPC server with open opc?

    I am not using the gateway server - direct connection on same computer.

    I can write 4 values to the OPC server fine.

    I can usually read 1 value fine.

    If I read say 4 values, it fails 99% of time (timeout).

    Anyone else had this problem?

     
  • Are you doing group based reads, or instantaneous reads?

    If instantaneous reads, then the likely problem is your group build timeout (ya, i know, sounds confusing, but check it out - everytime you read, you have to create a read-group  - so even an instantaneous read will build a group, read the data, then close the group… a group based read will build the group, read the data, leave the group open, wait a little while, read again, wait a little while, read again, so on and so on…)

    serial, token ring, or older / congested networks (even some large ethernet networks) will benefit from read calls as follows…

    group based -

    opc.read(WHATEVER-YOU-WANTED-TO-NORMALLY-READ, group=SOMENAME, timeout=TIMEOUT-IN-MILLISECONDS)

    for example -

    opc.read(ARRAY-OF-TAGS-TO-READ, group=GROUP_READ_1, timeout=30000)

    this will yield a 30 second connection period - the default is 5 seconds I believe.  So you can try 15000 (15 seconds), or 30000, but I don't think you'll need more than 60000 even with a horrendous network.

     
  • Markus Clarkus
    Markus Clarkus
    2010-12-25

    Thanks for the tip - yes I was doing instantaneous reads. I will try group reads and have a go at updating the documentation.

    Thanks,
    Mark.