I’m using potentiometers and the A/D convertors to simulate flow control valves, turbine speed, generator loading, etc. Plus 5 volts on one side of the pot and GRD on the other side. Middle tap goes to the A/D card.
Well… turns out there is a resistor voltage divider on the A/D card. Putting the pot directly to the card affects the resistance (makes the pot look like an audio taper instead of a linear taper). Quick email to AB Electronics and they solved my problem. I should have purchased the differential A/D cards instead of the single ended. Thinking back to 1984, I did use differential input A/D chips with +/- 5 input. But no matter, their solution of removing the resistor divider network was a great workaround.

Since now I’m going straight into the A/D chip, I needed to change the voltage on the pots from +5 to +2.048 (which is max input to the A/D chip). No problem. I found a single chip voltage reference card that will work. Cut and soldered a few wires and the rotary controls are up and running.