ADLINK PCM-9112+ - Manual (Page 84)

76 • Calibration
6.2 VR Assignment
There are five variable resistors (VR) on the PCI-9112 board for making
adjustments on the A/D and D/A channels. The function of each VR is
specified in Table 6.1.
VR1 A/D bipolar offset adjustment
VR2 A/D full scale adjustment
VR3 D/A channel 1 full scale adjustment
VR4 D/A channel 2 full scale adjustment
VR5 A/D unipolar offset adjustment
VR6 D/A reference voltage adjustment
VR7 A/D programmable amplifier offset adjustment
Table 6.1 Functions of VRs
6.3 A/D Adjustment
To calibrate the analog input channel, please follow the procedures
described below. Note that whether unipolar or bipolar input mode is applied,
programmable amplifier offset should be calibrated first. Moreover, when A/D
input configuration is bipolar, you should only follow the bipolar calibration
procedure. Performing a unipolar calibration on a bipolar configuration will
reduce the A/D input accuracy and vice versa.
6.3.1 A/D Programmable amplifier offset Calibration
1. Connect A/D channel 0 (AI0) to ground (GND).
2. Trim the variable resistor VR7 to obtain a reading as close as
possible to 0 (at most 0.5).
6.3.2 A/D Bipolar Calibration (Gain = 1, i.e. input range = +/-
5V)
1. Adjust the voltage calibrator’s voltage output to –4.9987V (i.e. –V
full
scale
+ 1/2 LSB). Apply this signal to A/D channel 0.
2. Trim VR1 to obtain a reading which toggles between 0 and 1.
3. Adjust the voltage calibrator’s voltage output to +4.9963V (i.e. +V
full
scale
-- 3/2 LSB). Apply this signal to A/D channel 0.
4. Trim VR2 to obtain a reading which toggles between 4094 and 4095.