While selecting your vacuum pump, the various units may look mysterious to you. So let’s clarify a little about the most important vacuum measurement units to help you understand what they are.
There are several units widely used in vacuum industries such as torr, mbar (bar), pascal and micron. The use of vacuum measurement units is regional: torr is commonly used in America, mbar is the preferred unit in Europe and pascal is popular in Asia.
In 1643, Evangelista Torricelli, an Italian physicist developed the first Barometer, a mercury filled glass tube. He carried out experiments with Hg (chemical symbol of mercury) to measure the presence of air. In honor of Torricelli, the millimeter of Hg unit was renamed as the Torr in the 1970s. One mmHg is equal to one Torr, approximately.
In Europe, people measure things mostly in metric terms. The vacuum measurement unit is the millibar or mbar in general use. Millibar was originally introduced based on the bar unit by Vilhelm Bjerknes, a Norwegian meteorologist. One mbar equals 0.75 Torr, or 100 Pa.
The pascal unit (symbol: Pa) is named after Blaise Pascal, the famous French mathematician and physicist . In 1646 he repeated the Torricelli experiment on a hill to reveal that the height of the mercury column changed at distinct altitudes. One Torr is equal to about 133 Pa.
The unit micron can be found in some vacuum industries. The mm of Hg was divided into 1000 smaller parts which were called microns. The word micron means a one-millionth part of a meter. One mmHg or one Torr equals 1 000 micron. One pascal is equal to 7.5 micron.
When you see some description like deep vacuum of 150 Micron, check it: It equals to 20 Pa or 0.2 mbar, which level is known as rough vacuum. Such vacuum can be generated by a single stage pump. However, you may find 2 Pa instead of 20 Pa in some circumstances. As an end user, you don’t need to understand the difference between partial and total ultimate pressure. Just remember it’s tricky to read 2 Pa because you don’t really have it. The figure of a partial ultimate pressure is much smaller but it makes no any sense. Likewise, the level of a dual stage pump can be considered as medium vacuum and the real vacuum is 2 Pa or 0.02 mbar which is equal to 15 Micron.
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