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If you precisely calibrate a D/A output range, you can use the it with
the CALB.EXE program to calibrate the card's A/D input. To calibrate
the ±10 V A/D range, first calibrate the 0 to 10 V D/A output. To
calibrate the ±5 V A/D range, first calibrate the 0 to 5 V D/A output.
Connect a reference voltage within the range ±10 V to the reference
input of the D/A channel to be calibrated. You can use the on-board -5
V (-10 V) reference or an external reference. Adjust the full scale gain
and zero offset of the D/A channel with VR3 and VR4. Use a precision
voltmeter to calibrate the D/A output.
1. Set the D/A data register to 0 and adjust VR4 until the output
voltage equals 0 V.
2. Set the D/A data to 4095 and adjust VR3 until the D/A output
voltage equals the reference voltage minus 1 LSB, but with the
opposite sign. For example, if V
+4.9988 V. If V
Regular and accurate calibration procedures ensure maximum possible
accuracy. The CALB.EXE calibration program leads you through the
whole A/D offset and gain adjustment procedure. The basic steps are
outlined below:
1. Short the A/D input channel 0 to ground and measure the voltage at
TP1 on the PCB (see the figure in Appendix B). Adjust VR5 until
TP1 is as close as possible to 0 V.
2. Connect a DC voltage source with value equal to 0.5 LSB (such as
the D/A output) to A/D Channel 0 (pin 1 on connector CN3).
3. Adjust VR2 until the output from the card's A/D converter flickers
between 0 and 1.
4. Connect a DC voltage source with a value of 4094.5 LSB (such as
the D/A output) to A/D channel 0.
5. Adjust VR1 until the A/D reading flickers between 4094 and 4095.
6. Repeat steps 2 to step 5, adjusting VR1 and VR2.
is -10 V, V
should be +9.9975 V.
ref
out
is -5 V, then V
ref
Appendix D Calibration
should be
out
69
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