Measurement Computing PCM-DAS16D/12 - Manual (Page 22)

reduce the overall common mode voltage, or add isolated signal conditioning between
the source and your board.
4.2.6 Isolated Grounds / Single-Ended Inputs
Single-ended inputs can be used to monitor isolated inputs, though the use of the dif-
ferential mode will increase you system’s noise immunity. The diagram below shows
the recommended connections is this configuration.
18
System with a Large Common Mode Voltage,
Connected to a Differential Input
+
-
L arge
comm
on
m
ode v
oltag
e
be
tween
signa
l
sou
rce &
A/D
board
GND
Isolation
Barrier
When the voltage difference
between signal source and
A/D board ground is large
enough so the A/D board’s
common mode range is
exceeded, isolated signal
conditioning must be added.
+
-
Input
Amp
To A/D
A/D Board I/O
Connector
LL GND
CH High
CH Low
10 K
10K is a recommended value. You may short LL GND to CH Low
instead, but this will reduce your system’s noise immunity.
Isolated Signal Source
Connected to a Single-Ended Input
I/O
Connector
+
-
Input
Amp
To A/D
LL GND
CH IN
A/D Board
+
-
Isolat
ed
signa
l
sour
ce