Using Non-Referenced Single-Ended (Nrse) Connections For Floating Signal Sources - National Instruments NI USB-621x User Manual

Chapter 5 Connecting AI Signals on the USB-6210/6211 Devices
Using Non-Referenced Single-Ended (NRSE) Connections for Floating
Signal Sources
NI USB-621x User Manual
inputs; be aware that there is some gain error from loading down the source,
as shown in Figure 5-4.
AC Coupled
Floating
Signal
Source
Figure 5-4. Differential Connections for AC Coupled Floating 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.
Figure 5-5 shows a floating source connected to the DAQ device in NRSE
mode.
Floating
Signal
Source
Figure 5-5. NRSE Connections for Floating Signal Sources
All of the bias resistor configurations discussed in the
Connections for Floating Signal Sources
resistors as well. Replace AI– with AI SENSE in Figures 5-1, 5-2, 5-3,
and 5-4 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
AC Coupling
+
V
s
–
with Balanced Bias Resistors
+
V
s
–
R
section apply to the NRSE bias
5-8
AI+
AI–
AI SENSE
AI GND
AI
AI SENSE
AI GND
Using Differential
ni.com