National Instruments AT-MIO-64F-5, User Manual

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Chapter 2 Configuration and Installation
© National Instruments Corporation 2-21 AT-MIO-64F-5 User Manual
Table 2-5. Recommended Input Configurations for Ground-Referenced
and Floating Signal Sources
Type of Signal Recommended Input
Configuration
Ground-referenced (nonisolated outputs, plug-in instruments) DIFF
NRSE
Floating (batteries, thermocouples, isolated outputs) DIFF with bias resistors
RSE
Differential Connection Considerations (DIFF Input Configuration)
Differential connections are those in which each AT-MIO-64F-5 analog input signal has its own
reference signal or signal return path. These connections are available when the AT-MIO-64F-5
is configured in the DIFF input mode. Each 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 the AT-MIO-64F-5 is configured for differential input, each signal uses two multiplexer
inputsÐone for the signal and one for its reference signal. Therefore, with a differential
configuration, up to 32 analog input channels are available. Differential input connections
should be used when any of the following conditions are present:
¥ You are connecting 32 or fewer signals to the AT-MIO-64F-5.
¥ Input signals are low level (less than 1 V).
¥ Leads connecting the signals to the AT-MIO-64F-5 are greater than 10 ft.
¥ Any of the input signals require 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 cause input signals to float within the common-
mode limits of the PGIA.