Pulling Values with Bad Quality (0X00)
From what we have tested when we pull values that have a bad quality, they return null either through the read API or axiom. When looking at it through the views I can see it has a value, is there a way to request the value of tag regardless of the quality?
We are on version 23.2
7 replies
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Hi ,
The Excel Add-in has an option to return the value regardless of quality. If you choose the Raw Data function, there is a Value and Value if Good checkbox. Choose Value.
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No luck, values using the excel add-in show empty.
Another odd thing is the timestamps don't line up. The tag shown is from the same view. -
I asked this question a while back (Steve, see case #14863). The short answer is you can't get Bad data. Some notable quotes from support:
I've talked with our engineers, and they said this is expected and there isn't a way to view data if it has a bad quality.
Quality gives the value its accuracy. If we get a bad not connected quality, the value is invalid. I'm not sure what the source is sending for a value, but we don't consider it valid and don't display it in a client because it's not accurate. The value may have some significance for troubleshooting what or why the source is sending it, but we wouldn't want operators thinking its valid data.
Which I understood but disagreed with. So they brought OPC spec into it.
In OPC (both classic OPC DA and OPC UA), a quality/status of “Bad – Not Connected” means the OPC server or client cannot currently communicate with the underlying data source for that tag/value.
The value may still show a number or previous value, but it should be considered invalid or stale. This is the OPC spec for the quality. We are just following the spec that the value can't be trusted, so why would a client display it?
There are 3 types of data good, uncertain, and bad. Uncertain could be a good or bad value and this would be the operators choice on how they want to handle it. This is why we include the option to include quality as well.I hope that helps. I don't see a feature request to allow this. Maybe ask for an optional checkbox in the API and Excel Add-In?
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I wouldn't expect a value to be returned if the quality is Bad; however, the add-in seems to be the exception, at least in version 26.6 that I'm running. Maybe this is a bug, but it's working as it should in 23.2. This is what I'm seeing in my system:
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