Is it possible to create a tag as a result of multiplication of two other tags?
Are you asking if it is possible to create a calculated tag that receives the product of 2 other tags values?
Yes, this is possible. I suggest you to look for PI Performance Equation Scheduler within the PI Server Application user guide and into the PI Performance Equation Reference (%PIHOME%\Help\PEReference.chm). Your equation could look like follows:
'Tag1' * 'Tag2'
You can use Performance Equation Builder add-in for PI System Management Tools (PI SMT -> Points -> Performance Equations).
Thanks Gregor, that looks like I want.
I've created a PE Point 'SINUSOID' * "SINUSOIDU' with a Event Scheduling linked to SINUSOID tag and I called it 'Eqq'. Later I've wanted to read my PE Point with PI WS and I've compared the values of Eqq and they aren't the same of SINUSOID values multiplicated by SINUSOIDU values.
Do you tell me why?
I've done what you did and to me results look as expected. You may see more archive values for tag 'Eqq' than for 'SINUSOID'. The reason for this is as follows:
Each new Snapshot event for tag 'SINUSOID' triggers a calculation but only a few Snapshot events path compression and make it into the archive. 'SINUSOIDU' is not the trigger but it's current value (Snapshot) will be used with calculations and compression is applied later. To compare 'Eqq' archive values against the product of what's been archived for 'SINUSOID' and 'SINUSOIDU' you would have to disable compression.
I've turnned off the compression option of SINUSOID, SINUSOIDU and Eqq and I still get the expected results.
If i try the GetPISanapshotData, the Eqq value isn't the product of SINUSOID value and SINUSOIDU value.
I've observed that the two PI Point and the PE Point have the same measures, one per second.
I've used PI DataLink -> Current Value to verify results. There's indeed a difference between DataLink and Microsoft Excel but I consider it marginal and cannot imagine this would be of any concern.
SINUSOID is the trigger for the calculation. Please note that the timestamp for SINUSOIDU can be older. PI Performance Equation Scheduler will use the current (snapshot) value for the calculation.
I am unsure what GetPISanapshotData refers to but when comparing calculation results, one always needs to compare current values at a particular time to verify if a result is wrong or not.
Does that help?
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