Calibration data in X Series EEPROM

[sar]

[Thanks again to the NI engineers that have prepared the X Series support for the MHDDK. Your work is much appreciated!]

I've been reviewing the X Series DDK manual and example code to get a handle on how things work, and I have

a couple questions about the calibration data that's retrieved from the EEPROM via eepromHelper and how it is used.

1) There are 4 AI "modes" containing 4 coefficients. What do these modes refer to? Do they have anything to do with different

ground reference modes (DIFF, RSE, NRSE)? I noticed that eepromHelper::getAIScalingCoefficients() only uses the coefficients

for the first mode (mode 0) to compute the scaling coefficients for a given voltage range. Is that OK no matter which ground

reference mode my application employs?

2) There is one AO "mode" containing the usual 4 coefficients. The eepromHelper reads in this mode as well as the different

voltage interval (gain, offset) pairs, but it doesn't use the mode coefficients to compute the scaling coefficients for a given

interval as is done for AI and as is implied in the DDK reference manual on p. 2-18. Instead, scaling coefficients are simply

the gain (C1) and offset (C0) for the chose voltage interval. Is the mode not relevant in the case of AO?

Sincerely,

Scott

[Christopher_T. · Accepted solution]

Hi Scott,

The AI Modes do not correspond to different ground references, but rather just the configuration for the AI frontend. The EEPROM actually has more information than the device needs. Therefore, as you have mentioned only mode 0 is used, this is because the other modes are not used.

The AO mode also does not use all of the data in the EEPROM. In this case, unlike the third order polynomial fit that is used for AI, the AO is simply a linear fit. Therefore only the gain and offset are used.

Regards,