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42 Micro Motion 7827 Digital Viscosity Meter
Calibration Check
A fourth fluid is used as an overcheck to verify the calibration for each viscosity range. Each check is
monitored by the Micro Motion Quality Assurance Department.
6.2.2 Density
The 7827 meter is calibrated within the standard shroud 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 calculation. The check is monitored by the
Micro Motion Quality Assurance Department.
Where viscosity correction is concerned, the temperature measurement from each viscosity
calibration fluid taken is translated into density through a previous characterization of the fluid using
prime standards. This method is used to assess the density offset due to viscosity for each viscosity
calibration range not including the 1 to 100 cP range, as the viscosity effect only becomes significant
at viscosities greater than 100 cP.
Once the meter has been calibrated with the necessary fluids a factory calibration certificate is
produced from the measurement data.
6.2.3 Primary standards
The fluids used in the viscosity calibration have been characterized for viscosity and density versus
temperature in between 15°C and 25°C. This is done using BS/U “U-tube” capillary viscosity meters
for kinematic viscosity measurement and pyknometers for density measurements. Both of these
methods are Primary Measurement Systems conforming to BS188 and BS733 Part 1 respectively.
The calibration of the calibration fluids is performed under closely controlled laboratory conditions.
A calibration certificate is issued. Calibrations are repeated, typically every six months, producing a
well documented history of the fluid.
6.2.4
Transfer standards
The Transfer Standard instruments used in the density calibration are selected instruments which are
calibrated by the British Calibration Service Laboratory and 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. A calibration certificate is issued. Calibrations are repeated, typically every six months,
producing a well-documented density standard.