Nematron Pointe Controller - Manual (Page 94)

Chapter 4: System Design and Installation Pointe Controller User Guide
92
In order to use single ended inputs, the ground connection must be very good.
The measurement devices must also be capable of being referenced to a common
ground.
Differential Inputs
There are cases when the individual analog inputs cannot be connected to a
common ground. In those cases, a differential input A/D converter should be
used.
With a differential analog input, both a positive and negative signal line must be
connected for each signal. The analog input module then measures the difference
between the positive and negative. The effect of one channel’s signal on another
channel’s signal should be as little as possible. That relationship of the effect on
the measured value of one channel to the value input on a second channel is
called “common mode.” The higher the “common mode rejection ratio (CMRR)”
the better.