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 manufacturer 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 as follows, assuming that the mv/v sensitivity rating of the transducer
and the bridge resistance are known.
(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 load cell
(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.)
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.
Calibration IL78A.3
AC Strain Gage Conditioner
Module
IL78A
