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Chapter 2
Analog Input and Temperature Sensor Measurements
Using Referenced Single-Ended (RSE) Connections for Floating
Signal Sources
Figure 2-9 shows how to connect a floating signal source to the DAQ device configured for RSE
mode.
Figure 2-9.
RSE Connections for Floating Signal Sources
Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes.
Ground-Referenced Signal Sources
A ground-referenced signal source is a signal source connected to the building system ground.
It is already connected to a common ground point with respect to the device, assuming that the
computer is plugged into the same power system as the source. Non-isolated 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 and 100 mV, but the difference can be much higher if power
distribution circuits are improperly connected. If a grounded signal source is incorrectly measured,
this difference can appear as measurement error. Follow the connection instructions for grounded
signal sources to eliminate this ground potential difference from the measured signal.
When to Use Differential Connections with Ground-Referenced
Signal Sources
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.
•
Two analog input channels, AI+ and AI–, are available.
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