Basics of Measurement & Units

Without a system of measurement units there would be no communicable and reproducible measurements.

The SI unit system (Le Systeme International d’Unites, the International System of Units, abbreviated SI, the modernized metric system) is used as the guide for the basic types of measurement devices.

It’s a logical starting point for understanding measurement & measurement devices.

There are three basic, fundamental measurements or base SI variables (units):

1. Length (meter), :
2. Mass (kilogram) and, :
3. Time (second).

Theoretically, all other quantities can be expressed in terms of these three.

However, under international agreement, the base variables (and units) of The SI system also includes:

  • electrical current (ampere),
  • thermodynamic temperature (kelvin),
  • amount of a substance (mole) and
  • luminous intensity (candela).

The international organization responsible for coordinating the standards for measurement of these related variables is called BIPM (for its name in French: Bureau International des Poids et Mesures),

In English the BIPM name translates to The International Bureau of Weights and Measures.

The national organization, or National Metrology Institue (NMI) usually responsible for maintaining the standards within each country is a government agency, such as those listed on a separate page here: http://www.measurementdevices.com/about-measurement/international-treaties-bipm-nmis.

A complete directory can be found on the BIPM website at: www.bipm.org/en/practical_info/useful_links/nmi.html.

From the base units, the SI system derives 21 additional variables and related parameters that are measurable.

This section will address devices for measuring five of the base SI units (each one of which is worthy of its own web site, as the temperature sensors one already is).

The others are scattered among the other measurement device classifications.

Notably, electrical current measuring devices are part of Electrical and Magnetic Measurement Devices.

For Technical Information on these sensors, they are indexed with links in the Basic SI Devices Area of our Web Links.

The following specific links take you to either external or internal pages where there are some vendors links to suppliers and/or makers of the various devices, sometimes with technical details added for interest.

* LENGTH — Dimensional Measurement Devices
* MASS — Mass and Weight Measurement Devices
* TIME — Measuring Time and Frequency
* PHOTOMETRY — Photometry and Radiometry Measurement Devices
* TEMPERATURE — Temperature Sensors and Measurements

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