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3.2 Analog Input Signal Connections
The PCM-3718 cards support either 16 single-ended or eight differential
analog inputs. Jumper JP3 selects the input channel configuration (See
2.2.3). The major difference between single-ended and differential input
connections is the number of signal wires per input channel.
3.2.1 Single-ended Channel Connections
Single-ended connections use only one signal wire per channel. The volt-
age on the line refers to the common ground on the card. A signal source
without a local ground is called a "floating" source. It is fairly simple to
connect a signal-ended channel to a floating signal source. A standard
wiring diagram looks like this.
Signal Input
+
T o A/D
Vs
-
A.GND
A.GND
3.2.2 Differential Channel Connection
The differential input configuration uses two signal wires per channel.
The card measures the voltage difference between these two wires, the
HIGH wire and the LOW wire. If the signal source has no connection to
local ground, it is called a "floating' source. A connection must exist
between LOW and ground to define a common reference point for float-
ing signal sources. To measure a floating source connect the input chan-
nel as shown below.
HIGH
+
+
+
Vs
V in
-
-
LO W
-
A.GND
25
Chapter 3
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