on 01-29-2010 10:32 AM
We have created a Tag Query in MII 12.1 with following details:
Server: PI Historian
Query: Tag
Mode: Statistics
Method: Total
The total function in PI is time weighted. It is adding up the raw values and then adjusting for the time period.
Is there a way that I can find event weighted value?
Hi Harsh,
you can connect to PI using the oledb connector. You have to install PI SDK on .net then connect using an OLEDB Dataserver to a windows server/system datasource.
You'll then be able to run queries on the pimean and piavg table. with a defined timestep in your where close.
ex: select sinusoid.2hr from pimean where timestep = 500s and time > 'sthg'
Cheers,
Arnaud
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Using PCo 2.1 to call the SUM function for getting the event-weighted values should help me.
API for PI Historian has a method to do this:
PIAdvCalcVal(<TAGNAME>,<Start Date>,<End Date>,"total","event-weighted", 0,1, 0,"xxxx")
Thanks for the help!
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While the PI API does directly support a call that would return the EventWeighted value, there is no way to make this call using the old UDS products - you would need to use one of the alternative suggestions already made.
The new PCo 2.1 release includes a PI Agent which supports a lot of additional functionality including new aggregate methods. The 2 methods pertaining to this thread are: "Integral" which works the way the current UDS works performing the total as TimeWeighted and the new "Sum" which would give you the total performed as EventWeighted.
Regards,
John
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Hi Harsh,
A simple way to get event weighted totals is to use Statistics - AVG and then multiply by the time period.
But I have to wonder why you would want to do such a thing? Time Weighted Averaging is not just industry standard when using process data via historians, it is also more correct in its representation of a process.
Regards,
Mike
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