National Instruments Multifunction RIO NI R Series, User Manual

Page: 35 / 71

Chapter 2 Hardware Overview of the NI 78xxR
R Series Multifunction RIO User Manual 2-16 ni.com
Common-Mode Signal Rejection Considerations
Fig
u
re 2-6 and Fig
u
re 2-9 show connections for signal so
u
rces that
are already referenced to some gro
u
nd point with respect to the
NI 783 x R/784 x R/785 x R. In these cases, the instr
u
mentation amplifier can
reject any voltage ca
u
sed by gro
u
nd potential differences between the
signal so
u
rce and the device. With differential inp
u
t connections, the
instr
u
mentation amplifier can reject common-mode noise pick
u
p in the
leads connecting the signal so
u
rces to the device. The instr
u
mentation
amplifier can reject common-mode signals when V+
in
and V–
in
(inp
u
t signals) are both within their specified inp
u
t ranges. Refer to
the NI R Series Multifunction RIO Specifications , available at
ni.com/
manual
s
, for more information abo
u
t inp
u
t ranges.
Analog Output
The bipolar o
u
tp
u
t range of the NI 783 x R/784 x R/785 x R AO channels is
fixed at ±10 V. Some applications req
u
ire that the AO channels power on
to known voltage levels. To set the power-on levels, yo
u
can config
u
re the
NI 783 x R/784 x R/785 x R to load and r
u
n a VI when the system powers on.
The VI can set the AO channels to the desired voltage levels. The VI
interprets data written to the DAC in two’s complement format. Table 2-3
shows the ideal AO voltage generated for a given inp
u
t code.
Note If yo
u
r VI does not set the o
u
tp
u
t val
u
e for an AO channel, then the AO channel
voltage o
u
tp
u
t will be
u
ndefined.
Table 2-3. Ideal Output Voltage and Input Code Mapping
Output Description AO Voltage
Input Code (Hex)
(Two’s Complement)
F
u
ll-scale range –1 LSB 9.999695 7FFF
F
u
ll-scale range –2 LSB 9.999390 7FFE
Midscale 0.000000 0000
Negative f
u
ll-scale range, +1 LSB –9.999695 8001
Negative f
u
ll-scale range –10.000000 8000
Any o
u
tp
u
t voltage —
AO Voltage
10.0 V
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