m series eeprom map / internal reference voltages

[fmhess]

I'm trying to write some calibration code for the m-series boards (I have a pci-6289). I can read the factory calibration coefficients from the eeprom (using the example code as a guide). However, what I want to be able to do is determine the coefficients on my own by reading the board's internal reference sources. By using the AI_Config_FIFO_Bypass register I can read various internal sources on the board, in particular 6.85V, 0.5V, 2V, 10V, and the analog outputs. Now, finally to get to my question.

Is it safe to assume the reference voltages are exactly 6.85V, 10V, etc. or is there information on the eeprom which gives the exact voltages of the references? There appears to be a floating point value in the eeprom at address 412 (the calibration area starts at 400) which looks like a voltage near 6.85V. But I don't see anything corresponding to the other voltage sources.

Also, I don't see any voltage references small enough to be used for the 0.2V or 0.1V input ranges. Am I supposed to just use a (calibrated) analog output channel to calibrate these input ranges?

[Hal_L]

Hi,

I am not clear on exactly what you are trying to do. However, the reference voltages on the card are accurate.

I would also like to point out that National Instruments provides a document with information for writing step by step calibration procedures in LabVIEW or C. Here is the link to this resource: Calibration Procedures. I hope that you find this information helpful.

Regards,

Hal L.

[DiegoF]

Offset 412 the reference voltage (float32 big-endian).  The internal calibration area starts at 400.  The calibration area offset is stored as a u16 (big-endian) at address 24.

This is the internal reference voltage read with the 10/-10 V range during external calibration.

Diego. 

[fmhess]

Okay, I've got it figured out now. I agree the 6.85V reference is indeed the calibration reference and its true voltage is on the eeprom. The 10V, 2V, and 0.5V references I mentioned before are actually the PWM calibration DAC used to calibrate the nonlinearity, described here:

http://zone.ni.com/devzone/conceptd.nsf/webmain/77D3DA4DAB6A767486256FA2005D27AD

The PWM DAC references can be varied between +-10V, +-2V, or +-0.5V from by writing pulse high/low times to the Cal_PWM register, you can even see them oscillate if you set the times large enough.