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Chapter 4
Analog Input
©
National Instruments Corporation
4-37
Fig
u
re 4-24 shows a differential connection config
u
ration.
Figure 4-24.
Connecting to the USB-6215/6216/6218 in Differential Mode
The differential connection config
u
ration allows the common-mode noise
voltage, V
cm
, to be rejected d
u
ring the meas
u
rement of V
1
.
Yo
u
m
u
st connect the negative lead of yo
u
r sensors and AI GND to a local
gro
u
nd signal on yo
u
r system.
Taking Referenced Single-Ended Measurements
Using the referenced single-ended meas
u
rement config
u
ration allows the
USB-6215/6216/6218 to take meas
u
rements on all AI channels when all
channels share a common gro
u
nd. Fig
u
re 4-25 shows an referenced
single-ended connection config
u
ration.
Note
If yo
u
leave the AI GND pin
u
nconnected, the signals float o
u
tside the working inp
u
t
range of the USB-6215/6216/6218. This can res
u
lt in
u
nreliable meas
u
rements beca
u
se
yo
u
cannot ens
u
re that the inp
u
t signal is within 10 V of AI GND.
* This signal name indicates the differential pair. Refer to Table 3-1,
, for a list of differential signal pairs.
AI 0+
AI 0– (AI 8)
*
M
u
x
AI 1+
AI 1– (AI 9)
*
AI GND
V
1
V
2
V
cm
ADC
PGIA
U
S
B-6215/6216/6218