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Prometheus CPU User Manual V1.44 Page 57
18. ANALOG CIRCUIT CALIBRATION
Calibration applies only to boards with the analog I/O circuit.
The analog I/O circuit is calibrated during production test prior to shipment. Over time the circuit
may drift slightly. If calibration is desired follow the procedure below. For analog I/O circuit
configuration see page 45.
Four adjustments are possible:
♦ A/D bipolar offset
♦ A/D unipolar offset
♦ A/D full-scale
♦ D/A full-scale
No adjustment for D/A offset is possible.
18.1 A/D bipolar offset
Potentiometer R66 is used for adjustment. Configure the circuit for Bipolar A/D mode. Input 0V to
any input channel and perform A/D conversions on that channel. The gain setting and single-
ended vs. differential mode do not matter. Adjust R66 until the A/D value is 0. To eliminate the
effects of noise, it is best to take a number of readings and average the values.
18.2 A/D unipolar offset
Potentiometer R67 is used for adjustment. Configure the circuit for Unipolar A/D mode. The gain
setting and single-ended vs. differential mode do not matter. Input 0V to any input channel and
perform A/D conversions on that channel. Adjust R67 until the A/D value is 0~1. To eliminate the
effects of noise, it is best to take a number of readings and average the values.
18.3 A/D full-scale
Potentiometer R74 is used for adjustment. Configure the circuit for Bipolar A/D mode ±10V. Input
9.9945V to any input channel and perform A/D conversions on that channel using a gain setting
of 1. Single-ended vs. differential mode does not matter. Adjust R74 until the average A/D value
is 32750. To eliminate the effects of noise, it is best to take a number of readings and average the
values.
Any input voltage and A/D reading near the top of the range (10V) can be used for the calibration
target voltage/reading. The above value is provided as an example.
18.4 D/A full scale
Potentiometer R89 is used for adjustment. Configure the D/A for 0-10V output range. Write the
output code of 4095 to all four D/A channels. Measure each one and adjust R89 until the average
reading is as close to 9.9976 as possible.