Upon request, or where the calibration range requested is beyond that of the secondary standard, a service is also provided for calibration of devices against a pressure balance.
Only instruments in generally good condition and of suitable quality and precision are accepted for calibration.
Instruments are normally calibrated in a cyclic series of rising and falling pressures, with measurements taken at between four and ten pressure points. The gas used for the calibration is normally either dry nitrogen or compressed air from the Laboratory’s general supply line. Some barometric pressure sensors are gas species dependent and it is important to specify the gas to be used for the calibration. Before calibration these instruments will be pressure cycled, over a pressure range just beyond the calibration range, to flush with the test gas.
Certificates of Calibration will normally show the values of pressure measured by the NPL standard and the corresponding corrections to be applied to the barometer tested.
Barometers submitted for calibration must have a pressure connection port to enable them to be connected to a closed pneumatic system, which includes an NPL standard, a ballast volume and means of altering the pressure.
Please note that NPL no longer provides a calibration service for mercurial barometers.
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