FAQs
FAQs Areas
Random FAQs
- 1 inch = 25.4 mm.
- The MSF h.f. services on 2.5, 5 and 10 MHz ceased at the end of February 1988 as they were of little use nationally, and more accurate methods were available for long-range comparisons.
- The instrument currently used to measure atmospheric pressure for the NPL online barograph is a good-quality, commercially available resonant pressure sensor.
- A blackbody source is an ideal, 'Planckian', radiator, i.e it emits thermal (visible and infrared) energy whose intensity at a given wavelength and temperature is given by the Planck Law of radiation.
- 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.
- When requesting a calibration it is reasonable to try and establish beforehand something about the measurement uncertainties that are likely to be provided on the ensuing certificate; unless they are going to be adequate there is not much point in asking for the calibration.
- There are a number of possible reasons for the difference, in addition to possible calibration errors.
What 'uncertainty in the measurement' will be quoted on my certificate of calibration? (FAQ - Force)
When requesting a calibration it is reasonable to try and establish beforehand something about the measurement uncertainties that are likely to be provided on the ensuing certificate; unless they are going to be adequate there is not much point in asking for the calibration.- In scientific circles the word balance has many meanings but in the context of weighing it originates from the abbreviation of beam-balance - where the weight of a sample or artefact contributes to the balance of moments of a beam about a central fulcrum.
- A difficult question perhaps impossible. In what way the minimum? Some would say seven have been introduced into the SI because seven are needed. It has also been argued that with the use of fundamental constants only one unit is needed.
All FAQs
- 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.
- In some situations.
- 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.