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Calibration Procedures
Chapter 5
AT-MIO-16D User Manual
5-6
© National Instruments Corporation
b. Take analog input readings from channel 0 at a gain of 1, and adjust trimpot R8 until a
reading of roughly two counts is returned.
c. Take analog input readings from channel 0 at the following gains:
both 1 and 500 for the AT-MIO-16DL
both 1 and 8 for the AT-MIO-16DH
d. Adjust trimpot R2 until the readings at each gain setting match to within one count of each
other.
2. Adjust the ADC input offset.
Adjust the ADC input offset by applying an input voltage across ACH0 and ACH8. This input
voltage is 1.22 mV, or 0 V +
1
/
2
LSB.
a. Connect the calibration voltage (1.22 mV) across ACH0 (pin 3 on the I/O connector) and
ACH8 (pin 4). Connect the ground point on the calibration voltage source to AI SENSE
(pin 19).
b. Take analog input readings from channel 0 at a gain of 1, and adjust trimpot R8 until the
ADC readings flicker evenly between zero and one.
3. Adjust the analog input gain.
Adjust the analog input gain by applying an input voltage across ACH0 and ACH8. This input
voltage is +9.99634 V, or V
+fs
-
3
/
2
LSB.
a. Connect the calibration voltage (+9.99634 V) across ACH0 (pin 3 on the I/O connector) and
ACH8 (pin 4). Connect the ground point on the calibration voltage source to AI SENSE
(pin 19).
b. Take analog input readings from Channel 0 at a gain of 1, and adjust trimpot R1 until the
ADC readings flicker evenly between 4,094 and 4,095.
Analog Output Calibration
To null out error sources that affect the accuracy of the output voltages generated, you must
calibrate the analog output circuitry by adjusting the following potential sources of error:
•
Analog output offset error
•
Analog output gain error
Offset error in the analog output circuitry is the total of the voltage offsets contributed by each
component in the circuitry. This error appears as a voltage difference between the desired
voltage and the actual output voltage generated and is independent of D/A setting. To correct
this offset gain error, set the D/A to negative full scale and adjust a trimpot until the output
voltage is the negative full-scale value
±
1
/
2
LSB.
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