Automating Manufacturing Systems - Process Control and ...

continuous sensors - 23.33
A Shield is a metal sheath that
surrounds the wires
Analog Input
Analog voltage source
+
-
IN1
REF1
SHLD
Figure 23.32
Cable Shielding
When connecting analog voltage sources to a controller the common, or reference
voltage can be connected different ways, as shown in Figure 23.33. The least expensive
method uses one shared common for all analog signals, this is called single ended. The
more accurate method is to use separate commons for each signal, this is called double
ended. Most analog input cards allow a choice between one or the other. But, when double
ended inputs are used the number of available inputs is halved. Most analog output cards
are double ended.