Kepware 6.12 not refreshing OPC client

[AT_9493596]

I have an OPC DA client (Citect) writing a value to a PLC via Kepware. The value written is 1, 2 or 3 and once the PLC has seen this, it resets the value back to 0. This works fine.

The problem I have is that Citect never sees the value reset to 0 and the value in Citect 'sticks' at 1, 2 or 3. I can however see that in Kepware (via Quick Client) the value is 0. It appears that Kepware is not giving an update to the Citect OPC client.

If I restart Citect, the value is successfully read as 0 (presumably because Kepware will then provide a general refresh of all tags to Citect). 

Is it possible for Kepware to get confused when a tag has two new values in quick succession? (0 to 1 and then 1 to 0) i.e. It sends the first change to the OPC client but not the second change.

I have seen something similar with another OPC server in the past where it would forget to send the second update. 

[rajskumar]

Hello,

Kepware itself acts as middleware and cannot directly perform read/write(A client is needed) operations and send them to the Citect DA client. Instead, the Citect DA client must perform a read after write to determine the final value (in this case, 0).

Regarding the Quick Client, it is important to note that it has a default update rate of 1000 ms. If the scan mode in the Kepware driver is set to “Respect Client specified Scan rate,” the Quick Client will read after each 1000 ms and update the value.

For further troubleshooting, I recommend trying a Sync/Async read in the Citect client to observe whether it updates the value to 0.

Feel free to reach out if you have any additional questions or need further assistance.

[AT_9493596 · Accepted solution]

Hi rajskumar,

Thank-you very much for taking the time to reply. My assumption was that the tag in question would be refreshed when it changed (like all the other tags that are read from the PLC). Therefore, when the PLC changed the tag back to 0, Kepware would pick this up and Citect would be notified. What I found was that Kepware does pick up the change but Citect isn't notified. 

I'm still surprised by this. However, I discovered a Citect OPC parameter that goes in the OPC section of the Citect ini file - "ReadAfterWrite" - and this solves it.      

You suggestion pointed me to look for this so thank-you again!

[cmorehead]

@AT_9493596 

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