Calibration of AI and AO cards

[cueball]

How do you calibrate the onboard reference voltage on both PXI-6259 and -6733?  Most of the documents show how to perform the external calibration on the AI or AO, but not to what happens to the internal reference voltage.  Does this get calibrated at the same time?  I could see this being the case for the -6733 since it is calibrated at 5V, but not the -6259 since it is calibrated at 7.5v.  Any ideas?

[Jennifer O]

Hi Cueball,

There is some detailed information available regarding External Calibration of our devices which you may find helpful.  The M-Series devices use an onboard precision reference. This information is located under the title New NI-MCal Calibration Methodology Improves Measurement Accuracy.

I will look into finding a clear answer for you regarding how the onboard reference is affected during external calibration (For both M-Series and AO) and post back.

Regards,

Jennifer O.
Applications Engineer
National Instruments

[Jennifer O]

Hi Cueball,

Although you already received an answer through email support I thought I would post an answer here for anyone else who may have a similar question. 

The drift in accuracy of the internal reference is corrected through a calibration factor which is updated during the external calibration process. The calibration procedures have been written to take a particular, accurate external voltage reference.  The internal refterence is corrected, even if it is at a different level than the externally provided source.  In the case of the M-Series calibration, a polynomial algorithm is used which facilitates accuracy at the full range of the card.

Regards,

Jennifer O.