It was originally defined as the pressure exerted by 760 mm of mercury at 0 ☌ and standard gravity (g = 9.80665 m/s2). Standard atmosphere is commonly used as a reference value for the average atmospheric pressure at sea level. The pascal unit is inconveniently small for many purposes outside of vacuum measurement, therefore the kilopascal (kPa) is more commonly used in everyday applications like meteorology and tire pressure. The pascal unit is completely independent of ambient temperature, local gravity and media density. Unlike other units such as psi, kgf/cm2, in H2O and in Hg the pressure value that the pascal unit represents is unchanging no matter where and how it is used. 4įor pressure, the SI system’s basic unit is pascal (Pa), which is N/m² (Newton per square meter, while Newton is kgm/s²). The word micron means a one millionth of a meter. The mm of Hg was divided into 1000 smaller parts which were called microns.
As vacuum technology advanced, it became necessary to have a more precise vacuum measurement unit than the mm of Hg. 3Ī micron refers to a micrometer of mercury. Millimeters of mercury, torr, and micron are three units of measure typically associated with the vacuum furnace industry while other fields of vacuum use pascals (Pa or kPa). The millitorr is not a commonly used pressure unit but tends to be used in scientific research or specialized manufacturing fields where very low vacuum pressures are measured. Millitorr is a very small pressure unit used for high vacuum measurements and is a 1/1000x multiple of the Torr pressure unit. The unit of barometric pressure (one millimeter of mercury, also written as 1 mm Hg) was named in honor of Torricelli. Over time, 760 millimeters of mercury came to be regarded as the “standard” atmospheric pressure. However, the torr is an exact quantity, whereas the mmHg is not due to variations in local gravity and temperature, and therefore the two pressure units should not be treated as the same.
The torr is closely related to mm Hg and the two values are almost exactly the same. It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644. The torr is a non-SI unit of pressure defined as 1/760 of an atmosphere. National Labs, Research and Development.Liquefied Natural Gas (LNG), Industrial Gas, Cryogenics.Geotechnical Monitoring and Structural Monitoring.
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