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Digital Trends and Trend Storage on Data Change

Chris

Hello,

We trend a lot of Digital tags, set to 2-byte storage method, but it would be so much better to storage them at a single bit. Also, we use the Wonderware Historian with the connector utility, all of our tags are configured as Analog with the 8-byte Trends stored as doubles and the 2-byte Trends stored as Integers. We have to set the engineering units to T/F and the range 0,1 to help sort them.

We run very fast trending, 100-250ms and it uses a lot of storage, we typically save about 13 months of data per site and I thought it might be possible to use the trigger in the Trend tag configuration to only store when the Variable tag data has changed. Has anybody done this? If so, what was your methods, workarounds and pitfall?

Thanks,

Chris

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  • Hi Chris,
    What version of the Wonderware Historian Connector are you using?
    In the V3.0 release the following change was made:
    - Connector stores "floating point (8-byte samples)" values from Citect SCADA as double in Wonderware Historian.
    - Connector stores "scaled (2-byte samples)" values from Citect SCADA as a float in Wonderware Historian.
    It is also possible to historize Digital Tags directly, without the need to configure a Trend tag. You are correct, 2-bytes of storage isn't the most efficient way to store a digital value.
    The only thing to be aware of is that Digital Variable Tags (which have Historize = True) get .Discrete appended to the tagname in the Historian DB. They also don't support backfilling, so you might miss samples while Connector is down.
    I agree that there should be a better way in Citect SCADA to store digital data more efficiently.
    With regard to storing Variable Tag data in a Trend only when it changes, your best option is to use Event Trends. The amount of engineering you need to do to make this work will depend on the protocol you are using. If you have OPC, DNP, ABCLX or IEC61850 then these drivers are Driver Runtime Interface enabled, which means they push samples into the Trend and Alarm system. If you have a traditional poll based driver (like MODNET, S7NT, etc.) then you will need to configure a tag or expression which controls when the Trend sample is taken (via the Trigger field).
    Kind regards
    Olivier
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  • Hi Chris,
    What version of the Wonderware Historian Connector are you using?
    In the V3.0 release the following change was made:
    - Connector stores "floating point (8-byte samples)" values from Citect SCADA as double in Wonderware Historian.
    - Connector stores "scaled (2-byte samples)" values from Citect SCADA as a float in Wonderware Historian.
    It is also possible to historize Digital Tags directly, without the need to configure a Trend tag. You are correct, 2-bytes of storage isn't the most efficient way to store a digital value.
    The only thing to be aware of is that Digital Variable Tags (which have Historize = True) get .Discrete appended to the tagname in the Historian DB. They also don't support backfilling, so you might miss samples while Connector is down.
    I agree that there should be a better way in Citect SCADA to store digital data more efficiently.
    With regard to storing Variable Tag data in a Trend only when it changes, your best option is to use Event Trends. The amount of engineering you need to do to make this work will depend on the protocol you are using. If you have OPC, DNP, ABCLX or IEC61850 then these drivers are Driver Runtime Interface enabled, which means they push samples into the Trend and Alarm system. If you have a traditional poll based driver (like MODNET, S7NT, etc.) then you will need to configure a tag or expression which controls when the Trend sample is taken (via the Trigger field).
    Kind regards
    Olivier
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