Using Non-Referenced Single-Ended (Nrse) Connections For Floating Signal Sources - National Instruments PCI-6251 User Manual

Chapter 4 Analog Input
Figure 4-7. Differential Connections for AC Coupled Floating Sources with
Using Non-Referenced Single-Ended (NRSE)
Connections for Floating Signal Sources
It is important to connect the negative lead of a floating signals source to AI GND (either directly
or through a resistor). Otherwise the source may float out of the valid input range of the NI-PGIA
and the DAQ device returns erroneous data.
Note (NI USB-62xx BNC Devices)
BNC devices, move the switch under the BNC connector to the FS position.
Figure 4-8 shows a floating source connected to the DAQ device in NRSE mode.
Figure 4-8. NRSE Connections for Floating Signal Sources
All of the bias resistor configurations discussed in the
Floating Signal Sources
AI SENSE in Figures 4-4, 4-5, 4-6, and 4-7 for configurations with zero to two bias resistors.
The noise rejection of NRSE mode is better than RSE mode because the AI SENSE connection
is made remotely near the source. However, the noise rejection of NRSE mode is worse than
DIFF mode because the AI SENSE connection is shared with all channels rather than being
cabled in a twisted pair with the AI+ signal.
Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer
Configuring AI Ground-Reference Settings in Software
to the
the DAQ Assistant.
4-16 | ni.com
Balanced Bias Resistors
AC Coupling
AC Coupled
Floating
+
Signal
V
s
Source –
Floating
+
Signal
V
s
Source
–
R
section apply to the NRSE bias resistors as well. Replace AI- with
M Series Device
AI+
AI–
AI SENSE
AI GND
To measure a floating signal source on USB
M Series Device
AI
AI SENSE
AI GND
Using Differential Connections for
section for more information about