NI 9237 Operating Instructions and Specifications
14
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sensors beca
u
se there may be significant resistance in the wiring to
the active resistor in the bridge.
The NI 9237 sh
u
nt calibration circ
u
itry consists of a precision
resistor and a software-controlled switch. Refer to the software
help for information abo
u
t enabling the sh
u
nt calibration switch for
the NI 9237.
Sh
u
nt calibration involves sim
u
lating the inp
u
t of strain by
changing the resistance of an arm in the bridge by some known
amo
u
nt. This is accomplished by sh
u
nting, or connecting, a large
resistor of known val
u
e across one arm of the bridge, creating a
known strain-ind
u
ced change in resistance. Yo
u
can then meas
u
re
the o
u
tp
u
t of the bridge and compare it to the expected voltage
val
u
e. Yo
u
can
u
se the res
u
lts to correct gain errors in the entire
meas
u
rement path, or to simply verify general operation to gain
confidence in the set
u
p.
Use a stable signal, which is typically the
u
nloaded state of the
sensor, first with the sh
u
nt calibration switch off and then again
with the switch on. The difference in these two meas
u
rements
provides an indication of the gain errors from wiring resistances.
Yo
u
can design the software application to correct s
u
bseq
u
ent
readings for this gain error.
