06-15-2012 02:54 AM
I have a number of PXI 6254 cards that I think need self calibrating as all channels on each card share the same offset of mA.
I have read as much of the help files as I can find on the various ways to perform calibration and think that Self Calibration is required however I am struggling to find out information on the nitty gritty of performing the Self Calibration.
See attached screenshot of the NI software that I am using with the configuration of rack and cards.
I can see the "Self Calibrate" button towards the top right of the picture but do not want to press it until I fully understand what it will do as don't want to risk messing up anything that is currently working as the system has been in use for some years.
I would expect a new screen to open up showing the calibration factors currently in use (there has been no "Internal Calibration") that are from the original "External Calibration" - I understand these are permanently stored in the EEPROM.
I would also expect a "Self Calibrate" Start button. Once the Self Calibrate is completed then there must be some option there to save in EEPROM - in a separate location to the "External Calibration" factors. Also there must be some option to revert back to the original "External Calibration" factors.
Please could someone point me in the direction of the relevant documentation or outline the basic process involved in performing a "Self Calibration"- including the way to get back to the current calibration if the "Self Calibration" doesnt make things better.
Many thanks in advance...
06-19-2012 05:03 AM
Hi MonteMonte and thanks for your questions and interest in calibration.
I have two documents that I think will answer most of your questions and give you a much better idea of what the calibration process does:
Firstly, this one is nice and concise:
Secondly, this one is highly detailed, and mostly should hold true for your multifunction DAQ card:
It sounds like all of your cards have been in the same conditions and experienced the same voltage drift over time, as such, I would expect the reference voltages for self-calibration (mentioned in those documents) would also have drifted the same amount for each card. I would therefore recommend a self-calibration, which should improve accuracy and maintain consistency accross cards. However, it seems there is no going back!
If you've had the cards for more than 2 years and accuracy is important to your measurements, then it might be worth getting a quote for external calibration. If you would like to explore this option with National Instruments, please let me know and I'll get someone to get in touch with you.
06-19-2012 01:56 PM
Thanks for the reply and info.
I have read through the detailed info that you sent but have a few specific questions:
1) When I press the "Self Calibrate" button in the "Measurement and Automation Explorer" - known as MAX what will happen?(as per original screen shot posted with question):
- Will a new screen open up with more options/buttons
- Will a new screen open up with a text box where I type in commands to query/command the PXI (as per detailed calibration instructions)?
- Will the card go away and immediately start an internal calibration?
This is important as I dont want to risk starting an internal calibration.
2) You wrote "However, it seems there is no going back!" - does this really mean that once I start a self/internal calibration then I cant go back to the original external/factory calibration that the PXI is currently using? (there has never been an internal calibration).
3) Is there not an in depth proceedure for Self Calibration of PXI 6254 cards, or even M series PXI cards?
I have found the following manual - as attached.
"CALIBRATION PROCEDURE -B/E/M/S/X Series-For NI-DAQ™mx"
This basically suggests there is a single command to start the self calibration but gives no more info about how to get back to the original factory internal calibration. Should I assume that this is not possible for the M series, even if your detailed calibration instructions suggest it is?
Many thanks in advance for your help...