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When single item's quality is not good, all of the items become null

support
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25 Dec 2025 15:11 #14523 by support

Replied by support on topic When single item's quality is not good, all of the items become null

Hello.
there is a single OPC call made for reading all the items you specify in ReadMultipleItems. And all results are thus returned at once.

What happens here is that when you include the "problematic" nodes, the OPC server takes much longer to process. Until has it has *all* results, *no* results can be returned to the client. While waiting for the results, QuickOPC times out. It cannot give you any data, because at that moment, that server had not returned any data yet.

This is one of the reasons why in OPC, subscriptions are highly preferred over periodic reads.

You could increase the timeout, or make two ReadMultipleItems calls, one with the "OK" items and then the one with "dangerous" items.

Regards

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sigasec
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24 Dec 2025 16:04 #14522 by sigasec

Replied by sigasec on topic When single item's quality is not good, all of the items become null

Thanks for reply.

1. If I remove the problematic nodes from the list (there are currently 2 of them), I get the rest 370 node values in under 100 milliseconds.
2. If I add the problematic nodes back, the first call to _easyDAC.ReadMultipleItems waits exactly the number of milliseconds specified as read timeout:
_easyDAC.InstanceParameters.Timeouts.ReadItem = 15000;
and then throws an exception:
The time alloted for the OPC DA operation has expired. The timeout value was 15000 milliseconds.
So, vtqResults.Succeeded is never true, and ErrorMessageBrief of every item in vtqResults is exactly the same:
The time alloted for the OPC DA operation has expired. The timeout value was 15000 milliseconds.

So when timeout is reached, why the entire results collection is invalidated?
Also, is OPC server reports that specific node's quality is not 192 (Good), why EasyDAC still waits for timeout instead of returning the actual VTQ?

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support
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18 Dec 2025 07:30 - 18 Dec 2025 07:30 #14505 by support

Replied by support on topic When single item's quality is not good, all of the items become null

Hello.

1. What makes you think that the observed data are not simply what the OPC server sends to the client?

2. Is "vtqResults.Succeeded" true or false for the remaining items?

3. If it is true, what is the QUality of those remaining items? If it is false, what is the error associated with them (for start, ErrorMessageBrief)?

Thank you

Last edit: 18 Dec 2025 07:30 by support.

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sigasec
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17 Dec 2025 23:32 #14504 by sigasec

When single item's quality is not good, all of the items become null was created by sigasec

We use QuickOPC 5.83 with .NET 8. Our app is Windows Service that queries local OPC-DA server with 373 node items every 1000 milliseconds. Normally, everything works just fine, but sometimes one of the node's quality differs from 192 (Good), and in this case all the items values become NULL. The code is below:

Code:

var results = new List<double?>();
var serverDescriptor = new ServerDescriptor(Parameters.OPCServerName);

var newVal = new List<DAItemDescriptor>();
foreach (var tag in Parameters.OPCTagList)
{
    newVal.Add(tag);
}

Stopwatch timer = new Stopwatch();
timer.Start();
_easyDAC.InstanceParameters.Timeouts.ReadItem = 10000;
var readParameters = new DAReadParameters(0); // Taking the measurement of the current time even if it has not changed
DAVtqResult[] vtqResults = _easyDAC.ReadMultipleItems(serverDescriptor, newVal.ToArray(), readParameters);

if (vtqResults.Length > 0)
{
    validMeasumentExist = true;
}
timer.Stop();

if (_isDebug_OPC_Read)
{
    Trace.WriteInfo("Elapsed milliseconds: " + timer.ElapsedMilliseconds.ToString() + ", vtqResults.Length=" + vtqResults.Length, true);
}


for (int i = 0; i < vtqResults.Length; i++)
{
    Debug.Assert(vtqResults[i] != null);

    
    if (vtqResults[i].Succeeded)
    {
        results.Add((vtqResults[i].Vtq.Quality == DAQualities.GoodNonspecific) ? Convert.ToDouble(vtqResults[i].Vtq.Value) : null); 
    }
    else
    {
        Trace.WriteException(new Exception(vtqResults[i].ErrorMessageBrief));
        results.Add(null);
    }
}

return results;

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