audio: Pressure measurement

Evidence: 100 • authority: 72

Pressure measurement is the measurement of an applied force per unit area by a fluid (liquid or gas) on a surface. Pressure is typically expressed in units of pascals in the International System of Units (SI). Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges, vacuum gauges or compound gauges (vacuum & pressure). The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge. A vacuum gauge is used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negativ…

Evidence: 52 • authority: 72

Evidence: 48 • authority: 72

Evidence: 40 • authority: 72

A McLeod gauge is a scientific instrument used to measure very low pressures, down to 10−6 Torr (0.133 mPa). It was invented in 1874 by Herbert McLeod (1841–1923). McLeod gauges were once commonly found attached to equipment that operates under vacuum, such as a lyophilizer. Today, however, these gauges have largely been replaced by electronic vacuum gauges. The design of a McLeod gauge is somewhat similar to that of a mercury-column manometer. Typically it is filled with mercury. If used incorrectly, this mercury can escape and contaminate the vacuum system attached to the gauge. McLeod gauges operate by taking in a sample volume of gas from a vacuum chamber, then compressing it by tilting…

Evidence: 29 • authority: 72

The Pirani gauge is a robust thermal conductivity gauge used for the measurement of the pressures in vacuum systems. It was invented in 1906 by Marcello Pirani. Marcello Stefano Pirani was a German physicist working for Siemens & Halske which was involved in the vacuum lamp industry. In 1905 their product was tantalum lamps which required a high vacuum environment for the filaments. The gauges that Pirani was using in the production environment were some fifty McLeod gauges, each filled with 2 kg of mercury in glass tubes. Pirani was aware of the gas thermal conductivity investigations of Kundt and Warburg (1875) published thirty years earlier and the work of Marian Smoluchowski (1898). In…

Evidence: 29 • authority: 72

A vacuum (pl.: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective vacuus (neuter vacuum) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is us…

Evidence: 26 • authority: 92

Evidence: 23 • authority: 92

Evidence: 23 • authority: 72