There are many kinds of instruments used for pressure measurement, which can be roughly divided into the following types according to their conversion principle.
1. Liquid column pressure gauge
Liquid column pressure gauge is based on the static principle, will be measured pressure into the height of the liquid column pressure measurement. Such instruments include u-tube manometers, single-tube manometers, inclined tube manometers, etc. Commonly used pressure indicators are alcohol, water, carbon tetrachloride and mercury. This kind of instrument has the advantages of simple structure, sensitive response and accurate measurement. The disadvantages are limited by the density of the liquid, narrow range of pressure measurement, when the pressure fluctuates violently, the liquid column is not easy to be stable, and there are strict requirements on the installation position and posture. Generally only used for measuring low pressure and vacuum degree, mostly used in laboratory.
2, elastic pressure gauge
The elastic pressure gauge is based on the principle of force deformation of the elastic element, the measured pressure is converted into the displacement of the element to measure the pressure. Common pressure gauges are spring tube pressure gauges, bellows pressure gauges, diaphragm (or membrane box) pressure gauges. This kind of pressure measuring instrument is simple in structure, firm and durable, cheap in price, reliable in work and wide in measuring range. However, the measuring accuracy of the elastic pressure gauge is not very high, and most of the use of mechanical pointer output, mainly for the production of on-site indication. When a signal is needed to be transmitted far, an additional device must be fitted.
Pressure sensor and pressure transmitter pressure sensor and pressure transmitter is to use some physical characteristics of the object, through different conversion elements will be measured pressure into a variety of electrical signals, and according to the change of these signals to measure pressure indirectly. According to the different conversion elements, pressure sensors and pressure transmitters can be divided into resistance type, capacitance type, strain type, inductance type, piezoelectric type, hall type and other forms. The biggest characteristic of this kind of pressure measuring instrument is that the output signal is easy to be transmitted far away, and it can be used together with various kinds of display, record and adjusting instrument conveniently, thus creating conditions for pressure centralized monitoring and control. It is widely used in production process automation system.
