Measurement Computing ADAC/5500 Series - Manual (Page 22)

ADAC Series PCI Boards 795 - 17 - ADAC/5500 Series User Manual
Fully-Differential for Grounded Signal Sources
See Figure 4.3 for an example of connecting Grounded Signal Sources in Fully Differential configuration.
Figure 4.3
Fully-Differential Configuration for Grounded Sources
Fully-Differential for Floating Signal Sources
Floating Signal Sources are typically wired to a data acquisition board in Single-Ended configuration,
however, when the Floating Source signal leads pass through an electrically noisy environment, Fully-
Differential configuration will give the best performance. When wiring Floating Signal sources in Fully-
Differential configuration, a resistor must be connected from the low side of the sources to analog ground
(AGND). These resistors create a return path to AGND for the bias currents of the instrumentation amplifier.
If a return path is not provided, the bias current will build up on stray capacitance, resulting in drift and
possible saturation of the amplifier.
If the input signal is DC coupled a 10 K ohm to 100 K ohm resistor must be connected from the input signal's
return to the data acquisition board's AGND.
For AC coupled input signals a 10 K ohm to 100 K ohm resistor must be connected from both input signal
high and input signal low to AGND.
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