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Chapter 2
Analog Input
Single-Ended Connection Considerations
Common-Mode Signal Rejection Considerations
E Series User Manual
A single-ended connection is one in which the device AI signal is
referenced to a ground that it can share with other input signals. The input
signal connects to the positive input of the PGIA, and the ground connects
to the negative input of the PGIA.
When every channel is configured for single-ended input, up to 64 AI
channels are available.
You can use single-ended input connections for any input signal that 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 10 ft. (3 m).
•
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.
Using the DAQ Assistant, you can configure the channels for RSE or NRSE
input modes. RSE mode is used for floating signal sources; in this case, the
device provides the reference ground point for the external signal. NRSE
input mode is used for ground-referenced signal sources; in this case, the
external signal supplies its own reference ground point and the device
should not supply one. Refer to the DAQ Assistant Help for more
information about the DAQ Assistant.
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 PGIA rejects both the common-mode
noise in the signal and the ground potential difference between the signal
source and the device ground, shown as V
Ground-referenced signal sources with single-ended connections to a
device are referenced to some ground point with respect to the device. In
this case, the PGIA can reject any voltage caused by ground potential
differences between the signal source and the device.
cm
2-26
in Figure 2-11.
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