# Metrology

## Ampere (unit of electric current)

Electric units, called “international units,” for current and resistance, were introduced by the International Electrical Congress held in Chicago in 1893, and definitions of the “international ampere” and “international ohm” were confirmed by the International Conference in London in 1908. Although it was already obvious on the occasion of the 8th CGPM (1933) that there …

## Kilogram (unit of mass)

The international prototype of the kilogram, an artifact made of platinum-iridium, is kept at the BIPM under the conditions specified by the 1st CGPM in 1889 when it sanctioned the prototype and declared: this prototype shall henceforth be considered to be the unit of mass. The 3rd CGPM (1901), in a declaration intended to end the …

## Tolerance

In Metrology, tolerance means the limit or acceptable limits of the variations of a physical dimension, a physical property of a manufactured object, of a system, or other measured values such as temperature, humidity, or time. In other words, it is the maximum allowable error in the measurement is specified in terms of some value. The tolerance in mechanical devices is …

## Standard conditions for temperature and pressure (STP)

Standard conditions for temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. STP should not be confused with the standard state of a material (pure substance, mixture, or solution) which is a reference point used to calculate its properties under different …

## Meter (or metre) unit of length

The unit of length is the meter (or metre), defined by the distance, at 0 °C under normal atmospheric pressure, between the axes of the two central lines marked on the bar of platinum-iridium (90% platinum and 10% iridium) kept at the Bureau International des Poids et Mesures and declared Prototype of the meter by the 1st …

## Parallax

Parallax is a deceptive change in the relative position of an object with a change in the position of the observer. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances. Parallax error The parallax error is due to the fact that the …

## Hertz (Hz)

The hertz (symbol Hz, named in honor of the 19th-century German physicist Heinrich Rudolf Hertz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

## International System of Units (SI)

The International System of Units universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement, used prevalently in science and international commerce. There are seven base units and symbols for the seven base quantities, which are assumed to be independent. These seven base units are essential for the …

## Linear Variable Differential Transformer (LVDT)

A linear variable differential transformer (LVDT) is one of the most popular electromechanical devices used to convert small mechanical displacements (of the order of a few millimeters or fractions of a millimeter) into amplified electrical signals. An LVDT provides an alternating current (AC) voltage output proportional to the relative displacement of a transformer core with respect to …

## Fidelity

Fidelity is defined as the degree to which a measurement instrument indicates changes in the measurand quantity without dynamic error. In metrology, it is said that a measuring instrument is all the more “faithful” the more it provides indications of little discordant value between them in the course of several measurements of a constant physical quantity. Fidelity error The fidelity error is …

Scroll to Top