Chapter 4
Connecting Signals
4-10
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Differential Connection Considerations
A differential connection is one in which the AI signal has its own reference
signal or signal return path. These connections are available when the
selected channel is configured in DIFF input mode. In DIFF mode, the AI
channels are paired, with ACH<
i>
as the signal input and ACH<
i
+8> as the
signal reference. For example, ACH0 is paired with ACH8, ACH1 is paired
with ACH9, and so on. The input signal is tied to the positive input of the
PGIA, and its reference signal, or return, is tied to the negative input of
the PGIA.
When you configure a channel for DIFF input mode, each signal uses
two multiplexer inputs—one for the signal and one for its reference signal.
Therefore, with a differential configuration for every channel, up to eight
AI channels are available.
You should 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.
Differential signal connections reduce noise pick up and increase
common-mode noise rejection. Differential signal connections also allow
input signals to float within the common-mode limits of the PGIA.
