Force, pressure and mass

Pressure standards and barometers

UKAS accredited calibration and bespoke services

Pressure standards

Pressure balances (deadweight standards) are used to generate accurate reference pressures for the calibration of pressure calibrators, transducers and gauges. NPL provides a UKAS accredited calibration service for both pneumatically (gas) - and hydraulically (oil) - operated pressure balances.

UKAS accreditation:

Gas-operated pressure balances to uncertainties of: 

3.5 kPa to 16 kPa:  0.0023 %
16 kPa to 700 kPa:  0.0021 %
700 kPa to 7 MPa:  0.0025 % + 0.25 ppm/MPa
7 MPa to 21 MPa:  0.0028 % + 0.50  ppm/MPa

Oil-operated pressure balances to uncertainties of:

500 kPa to 200 MPa:  0.0031% +0.24 ppm/MPa
200 MPa to 500 MPa:  0.0038 % +0.24 ppm/MPa

The calibration of a pressure balance determines its effective area and, where appropriate, a pressure dependent term (expressed as ppm area per MPa pressure) also known as a distortion coefficient. The masses of the piston and other floating elements can also be certified.

Customers’ pressure balances are calibrated against NPL’s working standards which are part of a hierarchy of working, reference and primary standards. Traceability to the SI comes through the dimensional measurement of the primary standard piston-cylinders and via mass standards. NPL can also calibrate the mass sets used with pressure balances.

Gas-operated pressure balances are calibrated using nitrogen and oil-operated pressure balances are usually calibrated using sebacate (Monoplex® DOS manufactured by the C P Hall Company).


Barometers are normally calibrated over the range of 75 kPa to 110 kPa against a standard barometer 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. The UKAS accredited calibration accuracy for this service is ± 5 Pa.

Where the calibration range requested is beyond that of the standard barometer, a service is also provided for the direct calibration of devices against a pressure balance.

Barometers (digital (electronic) and precision aneroid) must have a pressure connection port to enable them to be connected to a closed pneumatic system. Some barometric pressure sensors are gas species dependent and it is important to specify the gas to be used for the calibration.

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