With the transducer loaded as in step (f), adjust the Symmetry control (right
above the PHASE control adjustment) to obtain a dead weight reading equal to
that obtained in step (f).
If
dead weight calibration is not practical
and the transducer manufac-
turer has supplied a calibration resistor (or resistor value), install the
recommended calibration resistor. See Fig. 5
(j)
(k)
Perfom steps (b) thru (e). Now activate the SHUNT POSITIVE (SHP) terminal
and adjust the SPAN controls until the instrument output is equal to the Equivalent
Input value simulated by the installed resistor. Shunt is performed at zero load.
If a negative Equivalent Input value is also provided on the calibration sheet
of the transducer under calibration, activate the SHUNT NEGATIVE (SHN) terminal.
Confirm that the negative value can also be obtained. If necessary, adust the SYMMETRY
control to obtain the negative Equivalent Input value as listed on the calibration
document. The SYMMETRY control has approximately 7% authority, full scale.
If dead weight calibration is not practical and the transducer calibration
data is unknown, the Equivalent Input value for the factory-installed
calibration resistor can be approximated
mv/v sensitivity rating of the transducer
known.
as follows, assuming that
and the bridge resistance
the
are
(l)
(m)
where
X
=
Equivalent Input, % of full scale
R
b
=
bridge resistance, ohms
K =
transducer sensitivity, mV/V full scale
R
c
=
calibration resistance, ohms (59 k installed)
Sample Calculation: Assume that K = 3.000 mV/V for a 5000-pound loadcell
(fullscale) with a bridge resistance of 350 ohms.
49.4%
of full scale = 2472 pounds
X =
25000 R
b
K R
c
X =
59000 x 3
25000 x 350
=
ring, one unit can be designated the master, and the remaining units can be driven
from the oscillator contained in the master unit. The remaining units are designated
as slave instruments. To perform master/slave wiring, refer to Figure 4.
3. CALIBRATION
(cont.)
Calibration 5M78.3
Note: Above calculation is useful in applications involving non - star bridge shunt calibration strain gage
bridges (for example DC bridges, and slip ring type torque sensors). Rotary transformer type sensors
which use star bridge shunt circuit will not equate properly and the sensor's published calibration
data should be referenced.
