Advantech Carbon Monoxide Alarm PCI-1718 Series User Manual

Regular and accurate calibration ensures 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:

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 VR4 until TP1 is as 
close as possible to 0 V. 
Connect a DC voltage source with value equal to 0.5 LSB (such as the D/
A output) to A/D Channel O (pin 1 on connector CN3).
Adjust VR3 until the output from the card's A/D converter flickers 
between 0 and 1.
Connect a DC voltage source with a value of 4094.5 LSB (such as the D/
A output) to A/D channel 0.
Adjust VR2 until the A/D reading flickers between 4094 and 4095.
Repeat steps 2 to step 5, adjusting VR2 and VR3.
Select unipolar input configuration. Connect a DC voltage source with a 
value of 0.5 LSB (such as the D/A output) to A/D channel0. Adjust VR1 
until the reading of the A/D flickers between 0 and 1.