12
7.
SHUNT CALIBRATION FACILITY
Refer to Section 4.06 for Operation
This is applicable to resistance bridge transducers only, e.g. most load cells and
pressure transducers (not semi-conductor gauges).
The Shunt Calibration Facility can be used as:-
7.1
A Calibration Check.
When the prime calibration has been made by applying a
precise known pressure or load to the transducers as described in Section 5 or 6,
the R-CAL relay can be operated (normally with zero pressure or load applied) and
the output recorded as the Calibration Check figure. A quick check can then be
made at anytime by comparing new CAL outputs with the original.
Note
that if the output is not at zero when the CAL switch is operated, the true CAL
CHECK figure is the CAL output less the initial output.
7.2
A Shunt Calibration.
The shunt calibration method can be used to calibrate the
transducer and electronics without having to apply a known pressure or load to the
transducer.
7.2.1
Calculate the shunt calibration figure required from the data given on the transducer
Calibration Record Sheet (CRS).
From CRS - output for 100% = WmV
- output with shunt = YmV
Therefore output required in CAL is Y/W x required full scale output.
Note:
If CRS states shunt resistor different from the one fitted (59k ohm is
standard, other values to order) then it may still be possible to obtain a
calibration from:
CAL figure calculated x (R shunt / 59k) = new CAL figure
7.2.2
Set the COARSE GAIN switch for the required input sensitivity (see Section 4.5).
7.2.3
Connect the monitor and supply as detailed in Sections 2 and 3. With transducer
DISCONNECTED switch ON power. Set excitation voltage, via the EXCIT control,
to the value indicated in the transducer data.
Note, excessive excitation voltage or incorrect connection may irreparably damage
the transducer.
Connect transducer and allow a 20-minute warm-up period (for maximum accuracy)
7.2.4
Ensure no load or pressure applied to the transducer.
7.2.5
Operate CAL relay and adjust FINE GAIN control to give the required output as
calculated in 7.21.
