Table 17. NI sbRIO Analog Input Configuration
AI Ground-
Reference
Setting
Floating Signal Sources (Not
Connected to Building Ground)
Ground-Referenced Signal
Sources
Examples
•
Ungrounded thermocouples
•
Signal conditioning with isolated
outputs
•
Battery devices
•
Plug-in instruments with non-
isolated outputs
Differential
+
–
+
–
AI+
AI–
AI GND
Signal Source
+
–
+
–
AI+
AI–
AI GND
Signal Source
Referenced
Single-Ended
(RSE)
+
–
+
–
AI
AI GND
Signal Source
Ground-loop potential (V
A
– V
B
)
are added to measured signal.
NOT RECOMMENDED
+
–
+
–
AI
AI GND
V
B
V
A
Signal Source
Connecting Floating Signal Sources
A floating signal source is not connected to the building ground system, but has an isolated
ground-reference point. Some examples of floating signal sources are outputs of transformers,
thermocouples, battery-powered devices, optical isolators, and isolation amplifiers. An
instrument or device that has an isolated output is a floating signal source.
When to Use Differential Connections with Floating 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.
NI sbRIO-9637 User Manual
|
© National Instruments
|
33
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
