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4.2.4 Common Mode Voltage < +/-10V / Differential Inputs
Systems with varying ground potentials should always be monitored in the differential mode. Care is required to assure that
the sum of the input signal and the ground differential (referred to as the common mode voltage) does not exceed the
common mode range of the A/D board (+/-10V on the PCI-DAS1000). The diagram below show recommended connections
in this configuration.
4.2.5 Common Mode Voltage > +/-10V
The PCI-DAS1000 will not directly monitor signals with common mode voltages greater than +/-10V. You will either need
to alter the system ground configuration to reduce the overall common mode voltage, or add isolated signal conditioning
between the source and your board.
11
+
-
Input
Amp
To A/D
A/D Board
I/O
Connector
LL GND
CH High
CH Low
Signal Source
with Common
Mode Voltage
Signal source and A/D board
with common mode voltage
connected to a differential input.
GND
The voltage differential
between these grounds,
added to the maximum
input signal must stay
within +/-10V
System with a Large Common Mode Voltage,
Connected to a Single-Ended Input
I/O
Connector
+
-
Input
Amp
To A/D
LL GND
CH IN
A/D Board
L
arge common
mode voltage
between signal
source & A/D board
GND
Isolation
Barrier
When the volta
g
e difference
between si
g
nal source and
A/D board
g
round is lar
g
e
enou
g
h so the A/D board’s
common mode ran
g
e is
exceeded, isolated si
g
nal
conditionin
g
must be added.