National Instruments 321645c-01 User Manual

Chapter 2

Function Reference — Calibrate_1200

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 National Instruments Corporation

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NI-DAQ FRM for PC Compatibles

DAC1chan is the analog input channel connected to DAC1 when calOP is 3.

Range:

0 through 7.

calRefVolts is the value of the DC calibration voltage connected to calRefChan when 
calOP = 2. 

gain is the device gain setting at which you want to calibrate when calOP is 2 or 3. When 
you perform an analog input operation, a calibration constant for that gain must be available. 
When you run the 

Calibrate_1200

 function at a particular gain, the device only can be used 

to collect data accurately at that gain. If you are creating a set of calibration constants that you 
intend to use, you must be sure to calibrate at all gains at which you intend to sample.

Range:

1, 2, 5, 10, 50, or 100.

A calibration performed in bipolar mode is not valid for unipolar and vice versa. 

Calibrate_1200

 performs a bipolar or unipolar calibration, or loads the bipolar or unipolar 

constants (calOP=1, EEPROMloc=0), depending on the value of the polarity parameter in 
the last call to 

AI_Configure

 and 

AO_Configure

. If analog input measurements are taken 

with the wrong set of calibration constants loaded, you might produce erroneous data.

Calibrate for a particular gain if you plan to acquire at that gain. If you calibrate the device 
yourself make sure you calibrate at a gain that you are likely to use. Each gain has a different 
calibration constant. When you switch gains, NI-DAQ automatically loads the calibration 
constant for that particular gain. If you have not calibrated for that gain and saved the constant 
earlier, an incorrect value is used.

To set up your own calibration constants in the user area for both unipolar and bipolar 
configurations, you need to complete the following steps. The basic steps are to create and 
store both unipolar and bipolar ADC calibration constants, and modify the default load table 
so that NI-DAQ automatically loads your constants instead of the factory constants. 

Step 1. Unipolar calibration—Change the polarity of your device to unipolar (by using the 

AI_Configure

 call or use the NI-DAQ Configuration Utility in Windows). Call 

Calibrate_1200

 to perform an ADC calibration, as in the following example: 

status = Calibrate_1200 (device, 2, 1, EEPROMloc, calRefChan, 

grndRefChan, 0, 0, calRefVolts, gain)

where you specify device, EEPROMloc (say 1, for example), calRefChan, grndRefChan, 
calRefVolts, and gain.