24 hour vs 2 year specifications

[ShadyJN]

Good evening everyone,

I'm trying to find out where the 24 hour specification used in Calibration Executive comes from for some devices.

For example the PXI-4072 has the 2-year and 24-hour specifications laid out in the specifications manual. Yet I'm calibrating a PXIe-6358 Multifunction DAQ and notice that the specifications manual only shows specifications for 2 years and not for 24 hours yet the certification Calibration Executive shows gives a 2 year and 24 hour specification. 2-years being the as found specification and 24 hours being the as left specification

Is there a formula to derive 24 hour specifications from the 2 year specifications?

Are there certain sources of error that aren't included in the 24 hour specifications?

I'm performing a validation and verification on this procedure and cant accomplish this without being able to verify both sets of tolerances in the calibration executive certification.

Any guidance is greatly appreciated, Thank you!

Joe

[sunaenae]

Hi Joe,

Here are the 24-hour and 2-year specifications for that device: http://www.ni.com/pdf/manuals/370937t.pdf#page=89.

Hope that helps!

Thanks,

[Russ_B.]

Hello Joe,

Warranted 24 hour limits are not provided for the PXIe-6358 module.  The calibration procedure provides limits only for particular data points for 24 hrs and 2 year.  Those limits should not be taken as warranted specs.

The formula you're asking for is the same formula that is in the spec sheet (page 3) under the AI Absolute Accuracy Equation section:

http://www.ni.com/pdf/manuals/374453c.pdf

The only difference is that the "GainError" portion has an added component of voltage reference drift over time.  This error is rolled into the ResidualGainError variable.  

The major difference between the 24 hr calculation vs the 2 year calculation is that the contribution of the reference drift over time is almost 0 for the 24 hr case.  The other difference is that it is assumed that there is less of an ambient temperature change for the 24 hour case.  Since these limits are used to verify calibration we make this assumption knowing that calibration is done in a very stable temperature environment.   

I hope this helps.

Russell