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- The triple point temperature of a pure substance is the unique temperature at which the solid, liquid and vapour phases of the substance co-exist in thermal equilibrium. Such triple points make ideal reference points for the calibration of thermometers.
- Machines capable of undertaking force calibrations are known as force standard machines and they may be categorised as either primary or secondary.
- Platinum-iridium was chosen as the material for the kilogram for a number of reasons.
- The diagram below shows the approximate operating ranges of some commonly available pressure and vacuum measuring instruments.
- Values of atmospheric pressure in Teddington, measured at about 10 metres above sea level, going back to 1 January 1998 and shown both graphically and digitally, can be found on the historical pressure page of the NPL on-line barograph.
- We already can set limits on the drift over a long period by looking at the values obtained for fundamental constants that depend critically on mass.
- Buoyancy is the upward force exerted on an object when it is immersed, partially or fully, in a fluid - and strictly where the fluid is subjected to a gravitational force but is not in free fall.
- The frequency with which calibrations should be carried out is an important, if sometimes difficult, question; there is no hard and fast rule but there are two main considerations.
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- The following are answers to some frequently asked questions on NPL gas standards. If you cannot find the answer you are looking for please contact us.
- Metrology is a service discipline - responding to a perceived need for a particular measurement accuracy, either now or in the near future.
- When converting between pressure units consideration should be given to the number of significant figures to use, bearing in mind that many of the underlying conversion factors are not themselves exact and cannot be made so.
- This is the responsibility of the European Parliament and the Council of the European Union.
- The variation in the value of g across the earth's surface is about 0.5 % due to latitude, plus a change of approximately 0.003 % per 100 m altitude. Local topography and tidal forces also can have small effects.
- The variation in the value of g across the earth's surface is about 0.5 % due to latitude, plus a change of approximately 0.003 % per 100 m altitude. Local topography and tidal forces also can have small effects.
- To calculate a pressure value using a liquid column - for example a mercury barometer - or a pressure balance it is necessary to know the gravitational acceleration at the location of the instrument. It can be determined by measurement on site, calculation or interpolation of measured values.
- There are many different types of barometer but they fit into two broad categories - those containing mercury and those that do not.