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Chapter 4
Analog Input
for grounded signal sources to eliminate this ground potential difference from the measured
signal.
When to Use Differential Connections with Ground-Referenced
Signal Sources
Use DIFF input connections for any channel that meets any of the following conditions:
•
The input signal is low level (less than 1 V).
•
The leads connecting the signal to the device are greater than 3 m (10 ft).
•
The input signal requires a separate ground-reference point or return signal.
•
The signal leads travel through noisy environments.
•
Two analog input channels, AI+ and AI-, are available.
DIFF signal connections reduce noise pickup and increase common-mode noise rejection. DIFF
signal connections also allow input signals to float within the common-mode limits of the
NI-PGIA.
Refer to the
Using Differential Connections for Ground-Referenced Signal Sources
more information about differential connections.
When to Use Non-Referenced Single-Ended (NRSE)
Connections with Ground-Referenced Signal Sources
Only use NRSE connections if the input signal meets the following conditions:
•
The input signal is high-level (greater than 1 V).
•
The leads connecting the signal to the device are less than 3 m (10 ft).
•
The input signal can share a common reference point with other signals.
DIFF input connections are recommended for greater signal integrity for any input signal that
does not meet the preceding conditions.
In the single-ended modes, more electrostatic and magnetic noise couples into the signal
connections than in DIFF configurations. The coupling is the result of differences in the signal
path. Magnetic coupling is proportional to the area between the two signal conductors. Electrical
coupling is a function of how much the electric field differs between the two conductors.
With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and
the ground potential difference between the signal source and the device ground.
Refer to the
Using Non-Referenced Single-Ended (NRSE) Connections for Ground-Referenced
Signal Sources
section for more information about NRSE connections.
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