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Chapter 2
Configuration and Installation
© National Instruments Corporation
2-27
AT-MIO-16D User Manual
Ground-Referenced Signal Sources
A ground-referenced signal source is one that is connected in some way to the building system
ground and is therefore already connected to a common ground point with respect to the
AT-MIO-16D board, assuming that the PC AT is plugged into the same power system.
Nonisolated outputs of instruments and devices that plug into the building power system fall into
this category.
The difference in ground potential between two instruments connected to the same building power
system is typically between 1 mV and 100 mV but can be much higher if power distribution
circuits are not properly connected. If the grounded signal source is measured improperly, this
difference may show up as an error in the measurement. The connection instructions for grounded
signal sources below are designed to eliminate this ground potential difference from the measured
signal.
Input Configurations
The AT-MIO-16D can be configured for one of three input modes–NRSE, RSE, or DIFF. The
following sections discuss the use of single-ended and differential measurements, and
considerations for measuring both floating and ground-referenced signal sources. Table 2-10
summarizes the recommended input configuration for both types of signal sources.
Table 2-10. 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 Configuration)
Differential connections are those in which each AT-MIO-16D analog input signal has its own
reference signal or signal return path. These connections are available when the AT-MIO-16D is
configured in the DIFF mode. Each input signal is tied to the positive (+) input of the
instrumentation amplifier; and its reference signal, or return, is tied to the negative (-) input of the
instrumentation amplifier.
When the AT-MIO-16D is configured for DIFF input, each signal uses two of the multiplexer
inputs–one for the signal and one for its reference signal. Therefore, only eight analog input
channels are available when using the DIFF configuration. The DIFF input configuration should
be used when any of the following conditions are present:
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