Floating Signal Sources - National Instruments USB-6008 User Manual

Analog Input
Mode Connected to Building Ground)
•
Examples
•
•
Differential
(DIFF)
Referenced
Single-Ended
(RSE)

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.
Refer to Field Wiring and Noise Considerations for Analog Signals for more information. To
access this document, go to
When to Use Differential Connections with Floating Signal Sources
Use DIFF input connections for any channel that meets any of the following conditions:
• Your application requires input ranges other than ±10 V.
• The input signal is low level and requires greater accuracy.
Table 6. Analog Input Configurations
Floating Signal Sources (Not
Ungrounded thermocouples
Signal conditioning with
isolated outputs
Battery devices
Signal Source NI USB-6008/6009
AI+
+
– AI–
Signal Source NI USB-6008/6009
AI
+
–
ni.com/info
Ground-Referenced Signal Sources
Plug-in instruments with non-isolated
outputs
Signal Source
+
–
GND
+
Signal Source
–
GND
V
A
Ground-loop potential (V
and enter the Info Code
NI USB-6008/6009 User Guide | © National Instruments | 13
NI USB-6008/6009
AI+
+
AI–
–
NOT RECOMMENDED
NI USB-6008/6009
AI
+
–
V
B
GND
– V
A B
to measured signal.
.
rdfwn3
+
–
GND
+
–
) are added