Chapter 5
Calibration Procedures
© National Instruments Corporation
5-7
AT-MIO-16D User Manual
Gain error in the analog output circuitry is the product of the gains contributed by each
component in the circuitry. This error appears as a voltage difference between the desired
voltage and the actual output voltage generated, which depends on the D/A setting. This gain
error is corrected by setting the D/A to positive full scale and adjusting a trimpot until the output
voltage corresponds to the positive full-scale value
±
1
/
2
LSB.
Board Configuration
The calibration procedure differs if you select either bipolar or unipolar output configuration. A
procedure for each configuration is given below.
The calibration procedures presented in this chapter assume that the internal voltage reference
+10 V is selected for the analog output channel to be calibrated.
To calibrate your board to an external reference input (DC only), you must recalculate the
desired output voltages to calibrate to.
•
For bipolar output:
1 LSB = V
extref
/2,048 (therefore,
1
/
2
LSB = V
extref
/4,096)
V
-fs
= -V
extref
V
+fs
= V
extref
- 1 LSB
•
For unipolar output:
1 LSB = V
extref
/4,096 (therefore,
1
/
2
LSB = V
extref
/8,192)
V
-fs
= 0 V
V
+fs
= V
extref
- 1 LSB
In calibrating to your own external reference, you should write your own procedures using the
following procedures as a guide. Substitute your calculated voltages for those given.
Bipolar Output Calibration Procedure
If your board is configured for bipolar output and two's complement mode, which provides an
output range of -10 to +10 V, then complete the following procedure in the order given.
1. Adjust the analog output offset.
Adjust the analog output offset by measuring the output voltage generated with the DAC set at
negative full-scale (0). This output voltage should be V
-fs
±
1
/
2
LSB. For bipolar output,
V
-fs
= -10 V, and
1
/
2
LSB = 2.44 mV.
•
For analog output channel 0:
a. Connect the voltmeter between DAC0 OUT (pin 20 on the I/O connector) and AOGND
(pin 23).
b. Set the analog output channel to -10 V by writing -2,048 to the DAC.
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