- Classification systems are used to specify most aspects of modern weights and weight sets.
- The instrument currently used to measure atmospheric pressure for the NPL online barograph is a good-quality, commercially available resonant pressure sensor.
- The measurement uncertainties achievable with pressure gauges, particularly traditional circular 'dial' gauges, are often expressed in one of two ways - as a percentage of reading or as a percentage of full-scale reading and the differences can be very significant, particularly when working at pressures much lower than an instrument's full-scale.
- The International Temperature Scale of 1990 goes down to 0.65 K, below this, to 1 mK, is the Provisional Low Temperature Scale of 2000 (PLTS-2000).
- Download the complete 'Gas standards and measurements' brochure.
- 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.
- 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.
- 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.