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Chapter 4
Analog Input
signal path as previously described using the same value resistor on both the positive and
negative inputs; be aware that there is some gain error from loading down the source, as shown
in Figure 4-7.
Figure 4-7. Differential Connections for AC Coupled Floating Sources
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-6341/6343/6346/6361/6363 BNC Devices)
signal source on X Series USB 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.
4-16 | ni.com
with Balanced Bias Resistors
AC Coupling
AC Coupled
+
Floating
V
s
Signal
–
Source
Floating
+
Signal
V
s
Source
–
R
section apply to the NRSE bias resistors as well. Replace AI- with
MIO X Series Device
AI+
AI–
AI SENSE
AI GND
MIO X Series Device
AI
AI SENSE
AI GND
Using Differential Connections for
To measure a floating
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