National Instruments AT E Series User Manual
Page 67
Chapter 4
Connecting Signals
4-20
ni.com
Differential Connection Considerations (DIFF Input Configuration)
A differential connection is one in which the AT E Series device 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.
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 differential input, 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 (up to 32 channels on the AT-MIO-64E-3).
In DIFF input 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.
You should use differential 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 AT E Series device are greater
than 10 ft (3 m).
•
The input signal requires a separate ground-reference point or return
signal.
•
The signal leads travel through noisy environments.
Differential signal connections reduce picked-up noise and increase
common-mode noise rejection. Differential signal connections also allow
input signals to float within the common-mode limits of the PGIA.