National Instruments sbRIO-9637 - Page 34

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
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