FAQs
FAQs Areas
Random FAQs
- The MSF radio signal has a very long wavelength (5 km) which is comparible or larger than dimensions of the metalwork of buildings and pylons which act as a screening mesh and greatly reduce the signal strength.
- Calibrated Gas Mixtures (CGMs) are lower down in the gases hierarchy than PRGM or SGS.
- Multi-axis calibration is similar to single axis calibration but done once for each axis. There are very few sources of traceable dynamic force calibration – and certainly none in the force and frequency ranges measured by the majority of commercially available dynamic force transducers.
- 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.
- See our Good Practice Guidance Note.
- There are no standards established for the meaning of 12 a.m. and 12 p.m. and often a 24 hour time is less confusing.
- It depends on the exact item. Generally we try to offer calibrations in imperial units, where we have the facilities available.
- Accurate measurement of thermal conductivity is not quite as straightforward as the simple steady-state theory would suggest.
All FAQs
Why do we need both thermodynamic and practical temperature scales? (FAQ - Engineering Measurements)
Temperature is an intensive property and we can only measure thermodynamic temperature via measurable quantities which change with temperature. Because this is re-measured from time to time and the values revised, this scale may differ from the true thermodynamic temperature scale.- As UTC is running about one second per year faster than time based on the Earth's rotation (Greenwich Mean Time, or Universal Time), an extra second is occasionally inserted in the UTC time scale to let it fall behind and start catching up again.
- There are difficulties in displaying the time of day on internet pages...
- If we did, we would have to change the definition of the metre each time we were able to make a more precise laser.
- 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.
- Atmospheric pressure reduces with altitude for two reasons - both related to gravity.
- Users of the MSF service receive predominantly a ‘ground wave’ signal. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere and is much stronger at night, this can result in a total received signal that is either stronger or weaker.
- There are a few possible answers...
- This is used for the coating on radiometers because, when applied in the appropriate manner, it is one of the lowest reflectance surfaces that exist.