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Best method to read a lot of opc variables

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support
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12 Oct 2016 12:59 #4450 by support

Replied by support on topic Best method to read a lot of opc variables

It is correct in principle. Such a big read, however, can take long time, and the default timeout is set to 60 seconds.

It is possible to increase the timeout, e.g. like this (for 5 minutes):

client_.InstanceParameters.Timeouts.ReadItem = 5*60*1000;

You may also think of splitting the read in several chunks (but not very small ones). It is generally recommended to read as many items as possible in "one go", but it has one disadvantage, and that is, that you need to wait for all of them at once. Doing it in chunks gives you at least something sooner. Whether that's better or not depends on the use case.

Best regards

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mpp
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12 Oct 2016 10:09 #4448 by mpp

Best method to read a lot of opc variables was created by mpp

Hi, at the startup of my machine interface I need to read (and if a compilation variable is set write) more then 900 OPC variables which are machine parameters to control all the motors, parts, etc.

Actually I'm preparing a list of ItemDescriptors and read them in block with ReadMultipleItemsValue:

var itemDescriptors = new List<DAItemDescriptor>();
 
foreach (var item in variables)
{
    itemDescriptors.Add(new DAItemDescriptor(HandleOPC.PLC_ID + "." + item));
}
 
valueResults = client_.ReadMultipleItemValues(HandleOPC.OPCServerName, itemDescriptors.ToArray());

Is it correct?
If I scan the valueResults a lot of variables has the timeout exception.

What should I do?

Thanks in advance

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