Nematron OptiLogic Series - Manual (Page 13)

Optimation, Inc. (256)883-3050 13
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OptiLogic Series
Single Ended Inputs
Single ended inputs are all referenced to
the same ground point. In many applications,
single ended inputs produce significant
advantages. Single ended inputs require only
one ground connection and one signal input per
measured value. The result is reduced wiring
costs along with the reduced cost per channel on
the analog input module.
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.
Analog
inputs
Common
ground Converter Module
A/D
Converter
Bus
Interface
Analog
inputs
Converter Module
A/D
Converter
Bus
Interface
+
+
+
+
-
-
-
-