FAQs
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Random FAQs
- No. Since 1983 the metre has been re-defined in terms of the speed of light and is realised using laser wavelengths.
- 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.
- Liquid-in-glass thermometers can be used in varying ranges from around - 200°C to +600°C. In calibrating a liquid-in-glass thermometer one must consider the thermometer itself, the environment used for the calibration, and the standards used to provide the reference temperature.
- 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).
- Thermocouples are the most common sensors in industrial use due to the fact that they are small, simple, rugged and of low cost. They consist of two dissimilar conductors (wires) joined at a junction and contained in an insulator.
- NPL gets the traceability of its 300 mm diameter Master Flat from the surface of a pool of silicone oil, which conforms to the local radius of curvature of the earth and from which the departure from flatness can easily be calculated.
- 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.
- A force measurement system is made up of a transducer and associated instrumentation.
- The following list summarises the main standards documents relating to the measurement of thermal conductivity of construction materials, refractories and plastics.
- See our Good Practice Guidance Note.
All FAQs
- Yes, magnetic fields - and indeed magnetically permeable materials close to a balance - can effect a weighing result.
- Check plugs and parametric measurements are not mutually exclusive. It is NPL's opinion that for checking master gauges (i.e. not products) both check plugs and parametric measurements have their place.
- The Rugby radio station, with call-sign GBR, was brought into service in 1926 by the Post Office as a telegraphy station with world-wide coverage and a frequency of 16 kHz.
- Historically there have been a variety of units of mass and density, and approximate conversion factors to some of these are given below.
- The answers to some frequently asked questions about length metrology.
- To some degree yes. Ideally, the reflectivity of both the reference and test surface should be equal to give maximum contrast fringes.
- There are many good books and in addition NPL produces a range of Good Practice Guides relating to dimensional metrology.