What is performed during DMM Self Test

[colinowen]

There are self-calibration and self-test features available for the PXI4070 DMM cards. Whilst I can find information regarding what the self-calibration actually does, i can not find anything on the self-test other than:

Self Test - Performs a self test of the device.

Does the self-test perform the same testing as that performed as part of the self-calibration but without changing calibration data?

[colinowen]

Sorry guys, similar question for PXI5112 Scope card.

[RobSims]

Hi Colin,

Thanks for your post.

When a device carries out a self test, what occurs is a check of its base address(es), and interrupts. Essentially the self test is checks that the PC can communicate to the DMM/Scope correctly, and vice versa.

On the other hand, the self calibration checks device measurements against a set of constants that are stored on its EEPROM chip. This stored data relates to calibration constants obtained at the last external calibration (usually carried out at NI before shipping).
More info on what is carried out in a DMM's ADC self-cal can be found here and further DMM info can be found here.

In-depth calibration info on your scope card can be found here.

If you are looking to carry out a self calibration, I suggest allowing your PXI chassis to reach its operational temperature before cal'ing the card. This can be done by leaving the chassis powered on for 1/2 an hour or so.

I hope this helps.

Regards,

[Mark_S1]

I want to add to what R Sims wrote.
In our traditional devices, the NI PXI/PCI-4060 and PCMCIA-4050, self test works as mentioned above.
In our newest DMMs, the NI 4070/4071/4072, self test is more complete. We run some test that verify proper operation of digital components, and then we test the measurements of numerous internal analog paths.

Self Cal is only supported on the NI 4070/4071/4072 and it is what allows you to operate the DMM over a wide range of temperatures and maintain the accuracy of your measurements. During self cal, we take a long list of internal measurements (based on our stable and accurate on board references) and use them to calculate new, modified coefficients which we store in the user area of the EEPROM. The calculations use the last factory calibration as a starting point, but allow changes to the coefficients to take into account temperature changes. The factory calibration coefficients are written only during an external calibration to the factory area of the EEPROM, ensuring the calibration of your device is tracable to NIST. Keep in mind the calibration period of NI 4070/4071/4072 is every two years.

ADC Calibration is also only supported on the NI 4070/4071/4072 and is a per measurement gain modification. You can think of ADC Cal as a gain correction to your measurement, similar to how auto zero is an offset correction. In general, you will only need ADC Cal for high resolution measurements, such as 6 1/2 and 7 1/2 digits. It does not overwrite any calibration coefficients.

Mark S
DMM R & D Software

[colinowen]

Thank you for the response.

I have been trying to find further documentation regarding the self-test of the DMM (PXI-4070) and Scope card (PXI-5112). Also the presence, if any, of self-test and self-calibration routines for the Timer/Counter Card (PXI-6602).

Does anyone know if and where this information is documented?

Thanks for your help

Colin O

[MKWL]

Hi

I'm also looking for finer details of the self test. Does anyone know if these are stored somewhere?

Thanks

Matt

[Mark_E]

Hi Matt,

Basically, a self-test checks communication with the DMM and a few other functions to verify overall functionality. It's not meant to be an in-depth test or to self-calibrate you DMM, as mentioned previously. What kind of "finer details" are you looking for?

I sense that there may be more history behind your question and would like to understand the reason for your asking it. If you have concerns about how a unit is functioning, please let us know by either contacting us or by perusing or posting to the forums.

Have a great day!

[MKWL]

Hi Mark, thanks for your quick reply.

The details I'm after would be the 'few other functions to verify overall functionality', what parts are tested and how are they done. I'll be using the PXI-4071 along with 9 other PXI modules in a 1044 chassis as part of a test rack and I am required to look at methods for verifying it's functionality, as well as the other PXI modules.

From browsing the NI website and forums I've come across pockets of text that say the self test checks comms between the module and the computer, the ID of the module with the one registered in the computer, verifies proper operation of digital components, and test measurements of numerous internal analogue paths.

Are these all correct and if so are you about to provide a more in dept description?

Thanks
Matt

[Mark_E]

Hi Matt,

Self-test is meant to be a quick overall check of the DMM's functionality. That doesn't mean it is guaranteed ot be performing within specs or that nothing is amiss. NI-DMM has minor changes in each release that may alter the self-test routine slightly. What I say today might not necessarily be true tomorrow, etc.

To ensure you test the functionality you want at the paths of interest to you I recommend writing your own verify routine. I hope that helps!

[Mark_E]

Hi Matt,

Would you be OK with me contacting you offline? I just need your permission to access the email on your account.