Structure, principle and range selection of pressure gauge

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Structure, principle and range selection of pressure gauge

Operating principle

Inside the pressure gauge, the elastic deformation of the sensitive elements (Bourdon tube, capsule, diaphragm, bellows) is transmitted to the pointer by the conversion mechanism, cause the pointer rotating to indicate pressure value.

Bourdon-tube manometer: (The most common type of pressure gauge) The Bourdon tube sensor is  circle shape, its cross-sectional area is elliptical elastic C-shaped tube. One end of the Bourdon tube is fixed and another end is movable, its section shape is oval or flat. Commonly used materials are tin bronze (phosphor bronze, tin phosphor bronze), stainless steel and Monel alloy.

Capsule pressure gauge: The capsule sensor consists of two connected diaphragms of circular wave. The capsule sensor consists of capsule, transmission mechanism, adjusting mechanism, hairspring pointer and gauge dial.

The diaphragm manometer is mainly used to measure the pressure of corrosive media or Non-solidification and non-crystallized viscous media; the capsule manometer is used for measuring the micro and negative pressure of gas, it is suitable for measuring micro pressure and vacuum, the measurement range is generally -2000 ~ 4000Pa, and the accuracy level is generally 2.5%.

Pressure gauge classification:

According to measurement accuracy: Pressure gauge can be divided into precision pressure gauge, general pressure gauge.

The measurement accuracy of precision pressure gauge has 0.1, 0.16, 0.25, 0.4 and 0.05 respectively.

General pressure gauge measurement accuracy grade has 1.0, 1.6, 2.5, 4.0.

According to measurement range: divides into vacuum manometer, micro pressure manometer, low pressure manometer, medium pressure manometer and high pressure manometer.

According to applicable conditions: divides into vibration resistant manometer, heat resistant manometer, corrosion resistant manometer, impact explosion-proof manometer.

According to location of connection: divides into bottom connection and back connection.

 

Special pressure gauge:

Oxygen pressure gauges and ordinary pressure gauges can be the same structure and material, but oxygen pressure gauges must be oil forbidding treatment, because oil gets into the oxygen system will cause exploding.

Electric contact pressure gauge: be equipped with upper and lower limit contact mechanism, when the pressure deviates from the given range, it will output alarm signal.

Gauge dial selection:

The gauge dial of the pressure manometer commonly uses 60mm, L00mm, 150mm, 200mm, 250mm.

Generally according to the detection, instrument location and lighting to choose the appropriate gauge dial, in order to observe clearly. At the location of remote distance and relatively dark, advise to select gauge dial of 100mm above.

Range selection:

When the measured pressure varies widely, the maximum and minimum working pressures may not meet the above requirements at the same time, the selected instrument range shall first satisfy the maximum operating pressure condition. Standard series of pressure gauge measuring range: -0.1 ~ 0.06, 0.15 Mpa; 0 ~ 1, 1.6, 2.5, 4, 6, 10 x n Mpa ( n is a natural integer, which can be positive or negative )

In general, when the measured pressure is stable, the maximum working pressure shall not exceed 2/3 of the full range;

When the measured pressure pulsates or has large fluctuation, the maximum working pressure shall not exceed 1/2 of the full range;

In order to ensure the accuracy of measurement, the minimum working pressure shall not be less than 1/3 of the full range.

Accuracy selection

The accuracy of pressure measuring instrument is mainly determined according to the maximum allowable error on production, that is, the basic error of the instrument should be less than the maximum absolute error allowed by the actual measured pressure. In addition, the selection should adhere to the principle of saving, as long as the measurement accuracy can meet the requirements of application, there is no need to pursue the high-precision instruments.

Elastic component pressure gauge signal transmission mode

The elastic manometer is generally a direct reading instrument, the deformation of elastic components can also be converted to electrical output.

Potentiometer type: a slip-line potentiometer is installed in the bourdon tube manometer, and the voltage between the sliding contact and any end of the resistance depends on the position of the sliding contact, that is, depends on the pressure being measured.

Characteristic:  Relatively simple, output with good linearity, poor reliability

 Hall type: the conversion principle is based on the Hall effect of semiconductor materials. The greater the pressure is, the greater the difference of two area is. The greater the Hall potential which generates on the two sides of the Hall element perpendicular to the direction of the magnetic field and current is.

Characteristic: Hall potential Simple structure, high sensitivity, long life, sensitive to external magnetic field, poor vibration resistance

Differential transformer type: The movable core is connected to the free end of the elastic element and is located in the coil of the differential transformer. The higher the measured pressure is, the more the core deviates and the higher the output AC voltage is, so that the pressure value can be measured.

Features: good performance, small additional force, displacement range is large, in the central position of the output is not zero.

Generally, it is not recommended to use elastic pressure gauge with remote transmission. If need the remote display, advise to select the pressure transmitter with high precision, good stability and high reliability.

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