Solartron Mobrey 7828, Technical Manual

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78285000_AA
5-1
5
Calibration Check
5.1 CALIBRATION
5.1.1 FACTORY CALIBRATION
The 7828 Insertion Liquid Density Transmitter is calibrated within a standard physical
boundary (typically 52.5mm diameter) against Transfer Standard instruments traceable to
National Standards, prior to leaving the factory. Three fluids ranging in density from 1 to
1000 kg/m
3
are used to establish the general density equation constants. The
temperature coefficients are derived from the air point and material properties.
The calibration procedure relies on units being immersed in fluids whose density is
defined by Transfer Standards. Great attention is paid to producing temperature
equilibrium between the fluid, the unit under test and the Transfer Standard. In this way,
accurate calibration coefficients covering the required density range can be produced.
All instruments are over-checked on water to verify the calibration. This check is
monitored by the Solartron Quality Assurance Department.
5.1.2 CALIBRATION OF TRANSFER STANDARDS
The Transfer Standard instruments used in the calibration are selected instruments which
are calibrated by the British Calibration Service Calibration Laboratory and are certified.
Transfer Standard calibration uses a number of density-certified liquids, one of which is
water. The densities of these reference liquids are obtained using the Primary
Measurement System whereby glass sinkers of defined volume are weighed in samples
of the liquids.
Calibration of the Transfer Standard instruments is performed under closely controlled
laboratory conditions and a calibration certificate is issued. Calibrations are repeated,
typically every six months, producing a well documented density standard.
5.1.3 INSTRUMENT CALIBRATION
Each 7828 Transmitter is issued with its own calibration which is programmed in to the
instrument electronics before it leaves the factory. The calibration data is shown on a
calibration certificate supplied with the instrument, an example of which is shown overleaf.
The calibration contains four important pieces of data:
a. The instrument serial number.
b. The output signal/density relationship; this is based on three calibration points across
the sensor’s operating density range.