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Very slow periodic WriteItemValue() calls

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08 Sep 2014 13:38 #2245 by athyssen
Here is the code:

Stopwatch ST = new Stopwatch();
ST.Start();
OPCClient.WriteItemValue(ServerDesc, TagName, Value);
ST.Stop();

I would be interested in utilizing OPC Analyzer. Please send further instructions.

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08 Sep 2014 13:33 #2244 by support
It can be either caused by QuickOPC, or by the OPC server. I do not see a reason why it should be caused QuickOPC, but we need facts to establish the true cause.

Would you be willing to use a tool (OPC Analyzer) that will log the communication between your OPC client and the OPC Server? Note that your app needs to be changed temporarily to connect to OPC Analyzer instead (the OPC Analyzer acts as both a server and a client, forwards the commnunication and stores the log). The resulting log contains timing on the level function calls between the server and client, and from it, it should be possible to tell whether the delay is on the client side or server side.

Just to be absolutely sure, aren't you timing something else together with the Write? Can you post here a piece of code that does the timing please?

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08 Sep 2014 13:27 #2243 by athyssen
No one-shot reads. Only Subscribe-s and a single WriteItemValue.

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08 Sep 2014 13:25 #2242 by support
Are there also "one-shot" Reads in your application, or just Subscribe-s and Write-s?

Thank you

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08 Sep 2014 13:20 #2240 by athyssen
I have about a dozen boolean tags that I am monitoring using SubscribeItem with 100ms requested update rate. The tags match up to proximity sensors on a slow moving conveyor and change once every 1-3 seconds. Ping times to the PLC are < 1ms.

Once every 5-10 seconds I am writing a boolean value to a single item using:
WriteItemValue( ServerDesc, DAItemDesc, Value )

I have wrapped a timer around this call and sometimes get 33ms but frequently am seeing 600ms for this single write.

Any suggestions on what could be causing such a large delay?

Thanks.

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