I hope some one can help with this !!
I have been using the ADC with one instrument for some time with perfect results. This circuit is from a battery powered unit so I have had to wire in a 24V DC supply.
The additional instrument is 3 channel and mains powered and when I connect it to the ADC Terminal board all the voltages look correct but when it is plugged into the ADC the 3 new lines go to maximum.
I believe it could be something to do with different ground potentials but have not been able to figure it out!
I have attached a pdf of the circuit to make it easier to understand.