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Use ReadMultipleItemValues, or subscription/event handlers?

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03 Apr 2011 12:21 #348 by support
I was giving an answer to your question where you state " read ... tags ... every 2 seconds", i.e. periodically, and the answer (the recommendation to use subscription) holds for that scenario.
What you have described now is an opposite of what you described earlier. Consequently, the answer to it is different: And you are right, if you are not reading periodically and need a momentary snapshot of a set of values, then ReadMultipleItemValues is the way to go.

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03 Apr 2011 06:44 #347 by mpuig@mapex.es
Hello,
Ok, I understand that for individual tags, event handlers is the best solution.
But in case that part of these tags are recipes with a table format, for example :
component name1, quantity1, work order1, units1,
component name2, quantity2, work order2, units2, ...
we assume that we should use ReadMultipleItemValues to receive the whole table of components. In this case the duration of the read function is not important, because it will not be executed periodically.
Thank you.
Marc

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03 Apr 2011 04:31 #346 by support
Subscription and event handlers is definitely the right way to go. Repeatedly calling ReadMultipleItemValues is possible, but - especially with large quantities - can give worse performance and less precise timing.

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02 Apr 2011 18:24 #345 by support
From: M.
Sent: Saturday, April 02, 2011 5:51 PM
To: Zbynek Zahradnik
Subject: .....

Hello,

I have another question for you.

We have to develop an application to read 4000 tags from OPC server every 2 seconds and save the values to a database.

So, we are wondering if use the function ReadMultipleItemValues() with an array for the 4000 values is the best solution.

Do you recommend any other solution, like subscribe the items and use event handlers ?

Marc

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