National Physical Laboratory

Calibration of weights, all OIML classes

Mass facilities
Mass Services, Products & Facilities

NPL's wide range of facilities and knowledge ensures that NPL is well positioned to meet your calibration and training requirements.

NPL is responsible for the maintenance and dissemination of the UK’s National Standard for mass, which is a platinum-iridium cylinder known as kilogram-18. This is used as the basis for the whole mass scale of the UK.

We are able to provide a full UKAS-accredited calibration service for both individual weights, and weight sets, of OIML class E1, E2 and F1 in the range 50 kg to 1 mg. Weights of class E2 and F1 are normally calibrated by substitution weighing against NPL standards, whilst those of class E1 will normally be calibrated by a method of subdivision from an NPL secondary standard kilogram. In all cases the calibrations are traceable to kilogram-18. The supplied certificate of calibration will provide a value for the measured conventional mass (or weight in air) of each weight together with an uncertainty commensurate with the appropriate OIML weight class. The determination of the conventional mass relies upon knowledge of the density of the weight. If this is not supplied by the customer this can be determined by NPL or, in the case of E2 and F1 weights, estimated from knowledge of the weight's material.

Where required, we can also calibrate weights of known density to ‘reference level’ uncertainties lower than those required for OIML Class E1.

With a range of high accuracy automatic and manual comparators, NPL is also capable of weighing non-standard items that may otherwise be hard to calibrate. NPL’s range of comparators allows us to be very flexible to meet our customers’ requirements from large pressure balance ring-weights to performing Centre of Gravity measure'ents.

NPL can offer individual or group training in mass metrology, either in terms of a formal training course or, in what is becoming increasingly popular, by working alongside NPL staff for one or more weeks. Typical subjects covered during training include the calibration, use and handling of weights, the assessment of balances, and the theory and understanding of measurement uncertainties and their overall effect on calibration results.

Courses can of course be tailored to meet a customer’s specific needs on a wide range of mass and density topics. We are also available for on-site courses where NPL experts will come to you and be able to assist you in ensuring your mass and density measurements are carried out as accurately and efficiently as necessary.


Customer Service tel: +44 20 8943 6245

Last Updated: 27 Feb 2012
Created: 14 May 2009


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