4 differential outputs from gas sensors are fed into 4 differential inputs on the termination board. same results whether the board is plugged into the chassis or not.
If all outputs from the gas sensors are at zero and any of the 4 goes posiitive, the other 3 follw it up in value. There is not an exact match, maybe 75% of full value for the one that is actually going up. This a measureable phenomena ( a DMM will read it as well ). It only happens if the - input of the differential port is connected.
I have looked for CMV and so far have not found any.