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Chapter 2

Function Reference — SCXI_Cal_Constants

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 National Instruments Corporation

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NI-DAQ FRM for PC Compatibles

calibrating, and then call 

SCXI_Cal_Constants

 again at the end of your calibration 

sequence with 

opCode

 = 4 to copy the user EEPROM area to the default load area. That 

way there will be two copies of your new constants and you can revert to the factory 
constants using 

opCode

 = 4 without wiping out your new constants entirely.

Repeat the procedure above for each channel and range you want to calibrate. Subsequent 
calls to 

SCXI_AO_Write

 will use your new constants to scale voltage or current to the correct 

binary value.

EEPROM Organization
The SCXI-1122, SCXI-1124, SCXI-1126, and SCXI-1141 modules have an onboard 
EEPROM to handle storage of calibration constants. The EEPROM is divided into the 
following three areas:

•

The factory area is shipped with a set of factory calibration constants; you cannot write 
into the factory area, but you can read from it.

•

The default load area is where NI-DAQ automatically looks to load calibration 
constants the first time you access the module during an NI-DAQ session using an 
NI-DAQ function call, such as 

SCXI_Reset

, 

SCXI_Single_Chan_Setup

, or 

SCXI_AO_Write

. When the module is shipped, the default load area contains a copy 

of the factory calibration constants. When you write to the default load area using 

SCXI_Cal_Constants

, NI-DAQ also updates the constants in NI-DAQ memory.

•

The user area is an area for you to store your own calibration constants that you calculate 
by following the instructions above and using the 

SCXI_Cal_Constants

 function. You 

can also put a copy of your own constants in the default load area if you want NI-DAQ 
to automatically load your constants for subsequent NI-DAQ sessions.