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 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
non-referenced single-ended mode.
Figure 4-20.
Non-Referenced Single-Ended 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
non-referenced single-ended bias resistors as well. Replace AI– with AI
SENSE in Fig
u
res 4-16, 4-17, 4-18, and 4-19 for config
u
rations with zero
to two bias resistors. The noise rejection of non-referenced single-ended
mode is better than referenced single-ended mode beca
u
se the AI SENSE
connection is made remotely near the so
u
rce. However, the noise rejection
of non-referenced single-ended mode is worse than differential 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