- Machines capable of undertaking force calibrations are known as force standard machines and they may be categorised as either primary or secondary.
- See the Pressure Units FAQs.
- For a given composition and temperature, air density varies in direct proportional to air pressure and this reduces with altitude for two reasons - both related to gravity.
- The instrument currently used to measure atmospheric pressure for the NPL online barograph is a good-quality, commercially available resonant pressure sensor.
- The international system is a set of seven base units chosen to fulfil the requirements of science and technology. The selection of seven base units is a matter of choice.
- Yes but not enough to notice.
- This is the responsibility of the European Parliament and the Council of the European Union.
- It depends on the exact item. Generally we try to offer calibrations in imperial units, where we have the facilities available.
- There is no fixed period for the validity of a calibration certificate - it is not like your cars MOT certificate. However, measurement results stated on certificates are usually 'on the day' values and no allowance is made for subsequent drift.
- The MSF time signal provides a good service throughout the British Isles, with signal strengths greater than 100 µV/m at 1000 km from Anthorn (in Cumbria) in all directions.
- No, they are not. The internationally recognised SI unit for pressure is the pascal, abbreviated to Pa, and this is the unit realised by the primary measurement standards in the world's national metrology institutes to provide traceability for pressure measurements.
- The International Prototype Kilogram is not perfectly stable (its mass changes with time), the amount it changes cannot be known perfectly (there is no 'perfect' reference against which to judge it) and the values of the national copies cannot be monitored at the highest level of accuracy without being compared directly with it.
- The most accurate barometers are indeed the mercury primary barometers used at national measurement institutes. Most barometers, though, are secondary instruments rather than primary ones and when considering these it is not correct to say that those based on a mercury column are invariably more accurate than those that are based on an alternative principle.
- Yes there are - some are listed here.
- The time at which summer time begins and ends is given in the relevant EU Directive and UK Statutory Instrument as 1 a.m. Greenwich Mean Time (GMT).
- Up to a point yes, but unless a weight is of suitable design and material and in appropriate condition it will not be possible to give it a meaningful calibration and it would certainly be a waste of money.
- Give the weight a general inspection to check its construction, surface finish and the suitability of its magnetic properties.
- A number of factors need to be taken into account when considering sources for calibrating radiation thermometers.
- Yes - Saturated (or unsaturated) salt solutions, and certain other chemicals, can be used to generate an environment of a particular relative humidity in an enclosed space.
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