Chapter 4
Analog Input
4-36
ni.com
Connecting Analog Input Signals on
USB-6215/6216/6218 Devices
Yo
u
can connect the USB-6215/6216/6218 directly to a variety of devices
and other signal so
u
rces. Make s
u
re the devices yo
u
connect to the
USB-6215/6216/6218 are compatible with the inp
u
t specifications of the
mod
u
le.
When connecting vario
u
s so
u
rces to the USB-6215/6216/6218, yo
u
can
u
se
differential, single-ended, or a combination of single-ended and differential
connections.
Note
Yo
u
m
u
st always connect AI GND to a local gro
u
nd signal in yo
u
r system
u
sing
a low impedance connection. If yo
u
leave AI GND
u
nconnected, yo
u
cannot ens
u
re that
AI <0..31> are within 10 V of AI GND, and yo
u
r meas
u
rement may be
u
nreliable.
Taking Differential Measurements
To attain more acc
u
rate meas
u
rements and less noise,
u
se a differential
meas
u
rement config
u
ration. A differential meas
u
rement config
u
ration
req
u
ires two inp
u
ts for each meas
u
rement. The AI <0..31> description in
Table 3-1,
, lists the signal pairs that are valid for
differential connection config
u
rations with USB-621
x
devices.
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
* 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
