Good afternoon sir:
From the diagram you supplied, you are trying to measure two series current points in the same loop. To do this, you will need an isolator in one or both of the current loops before attempting to measure current with the 9203's different inputs, as all of its inputs have a common point at the negative terminal. As it is, the reading you are getting on the second channel is probably a float on the 9203 internal multiplexer. Even if you tried to use the two cards you have at the same time, you would be out of luck, as both the commons would still be tied together. Either get some external isolation in the loop to be measured, or a current measurement card with isolated inputs that you can float.
Good luck,
Dave
