Chapter 4
Analog Input
4-30
ni.com
Figure 4-19.
Differential Connections for AC Coupled Floating Sources
with Balanced Bias Resistors
Using Non-Referenced Single-Ended (NRSE)
Connections for Floating Signal Sources
It is important to connect the negative lead of a floating signals so
u
rce to
AI GND (either directly or thro
u
gh a resistor). Otherwise the so
u
rce may
float o
u
t of the valid inp
u
t range of the NI-PGIA and the DAQ device
ret
u
rns erroneo
u
s data.
Fig
u
re 4-20 shows a floating so
u
rce connected to the DAQ device in
NRSE mode.
Figure 4-20.
NRSE Connections for Floating Signal Sources
All of the bias resistor config
u
rations disc
u
ssed in the
Connections for Floating Signal Sources
section apply to the NRSE bias
resistors as well. Replace AI– with AI SENSE in Fig
u
u
rations with zero to two bias resistors. The noise
rejection of NRSE mode is better than RSE mode beca
u
se the AI SENSE
connection is made remotely near the so
u
rce. However, the noise rejection
of NRSE mode is worse than DIFF mode beca
u
se the AI SENSE
connection is shared with all channels rather than being cabled in a
twisted pair with the AI+ signal.
–
+
AI GND
V
s
AC-Co
u
pled
Flo
a
ting
S
ign
a
l
S
o
u
rce
AI+
AI–
AI
S
EN
S
E
AC Co
u
pling
–
+
AI GND
R
AI
S
EN
S
E
AI
V
s
Flo
a
ting
S
ign
a
l
S
o
u
rce