Wuhan Huatian Electric Power specializes in the production of vacuum measuring instruments (also known as portable vacuum detectors). The following is an introduction to vacuum measuring instruments for measuring vacuum pressure.

A subject that tends to cause confusion when specifying pressure sensors is the measurement of vacuum and its relationship to absolute pressure. Here are some definitions:

Absolute pressure – pressure relative to zero absolute pressure.

Gauge pressure – pressure referenced to local atmospheric pressure

Differential pressure – the difference in pressure between two points.

Vacuum – pressure below local atmospheric pressure.

As you can see from the above definition, absolute pressure is measured from absolute zero - the absence of pressure at all. There is no pressure at all in space, but on the surface of the Earth, the atmosphere exerts a pressure of about 14.7pa at sea level. A barometer is a device that uses a column of mercury to measure atmospheric pressure, which ranges from approximately 27 In Hg to 33 In Hg, depending on the weather. In addition to changing with the weather, local atmospheric pressure also depends on altitude. When you are at an altitude of 17,000 feet, atmospheric pressure is about half that of sea level.

A vacuum is any pressure below the local atmospheric pressure. It is defined as the difference between the local atmospheric pressure and the point of measurement. Vacuum can be measured correctly using a differential pressure sensor with a port open to the atmosphere. For example, if the negative port is connected to vacuum and the port is open to atmosphere, the sensor signal will increase as the vacuum increases. It will always indicate the correct vacuum level even if the local atmospheric pressure changes with the weather.

Absolute pressure sensors cannot directly measure vacuum. If connected to a vacuum, the signal from the absolute pressure sensor will decrease as the vacuum increases, but you can only know the actual vacuum if you know the local atmospheric pressure, since vacuum always refers to the atmosphere. Another way to think about a vacuum is that it is negative gauge pressure.

Local elevation affects vacuum measurements because it affects atmospheric pressure: no matter how powerful the vacuum pump is, you cannot pump 14 psi at an elevation of 6000 feet – because the atmosphere is only about 12.5pa and The pressure between vacuums cannot exceed this pressure.

In summary: It is best to use a dedicated instrument, a vacuum measuring instrument, to measure vacuum.

Replyant: Huatian Electric Power