The correct selection and installation of pressure gauge notice

1. Proper selection of pressure instruments

The correct selection of pressure meters mainly includes determining the type, range, range, accuracy and sensitivity of the meters, external dimensions, as well as the need for remote transmission and other functions, such as indicating, recording, adjusting, alarming, etc.

The main basis of pressure meter selection:

1.Process measurement requirements, including range and accuracy.In the case of static test (or slow change), the maximum pressure to be measured shall be two thirds of the full scale value of the pressure gauge;In the case of fluctuating pressure, the maximum pressure to be measured shall be one half of the full scale value of the pressure gauge.

The accuracy grades of the commonly used pressure measuring instruments are 0.05, 0.1, 0.25, 0.4, 1.0, 1.5 and 2.5.The maximum allowable error of the instrument is the product of the range of the pressure gauge and the percentage of the accuracy grade.

2.Properties of the medium under test, such as state (gas, liquid), temperature, viscosity, corrosiveness, degree of contamination, inflammability and explosive, etc.Such as oxygen meter, acetylene meter, with "oil" mark, special for the special medium of corrosion pressure gauges, high temperature pressure gauges, diaphragm pressure gauges.

3.Environmental conditions on site, such as ambient temperature, corrosion, vibration, moisture, etc.For example, shock - proof pressure gauges for vibrating environmental conditions.

4.Suitable for staff observation.According to the position of the measuring instrument and the lighting situation, choose the meter with different diameter (outside size).

Verification and calibration of pressure instruments

Instruments must be calibrated and calibrated before use.The instrument used for a long time should also be tested regularly, and its cycle should depend on the frequency and emphasis of use.When the instrument is equipped with long-distance transmission system and secondary instrument, it should be verified and calibrated together with the secondary instrument.

3. Proper installation of pressure instrument

For pressure detection, a measurement system is actually required.In order to achieve accurate measurement, in addition to the correct selection and verification of the instrument (calibration), we must also pay attention to the correct installation of the whole system.If only the seismic pressure gauge itself is accurate, its indication cannot fully represent the actual parameters of the measured medium, because the error of the measuring system is not equal to the error of the instrument.

The correct installation of the system includes the opening position of the pressure outlet, the reasonable laying of the connecting pipe and the correct installation position of the instrument.

1.Choose the position of the pressure outlet (1) avoid the area where the pipe bends, branches and the flow bundles form eddies.(2) when there is a protruding object in the pipeline (such as temperature measuring element), the pressure inlet should be taken in front of it.(3) when pressure must be taken near the regulating valve, the distance from the valve should be no less than 2 times of the pipe diameter if the pressure port is taken before the valve;If the pressure port is behind, the distance from the valve should not be less than 3 times the pipe diameter.(4) for a wide container, the pressure inlet should be in the area where the fluid flow is stable and there is no eddy current.In conclusion, the position of the pressure orifice determined in the process should ensure that the process parameters to be selected are measured.

2.Laying of connecting pipes

The horizontal section of the connection pipe shall be inclined to remove condensing liquid or gas.

When the measured medium is gas, the pipe should be inclined to the direction of the pressure outlet.When the measured medium is liquid, the catheter should be inclined to the direction of the gauge.When the measured parameter is a small value of differential pressure, the inclination can be slightly larger.In addition, if the catheter is located at the upper and lower corners, the discharge condensing device should be placed at the lowest point or the exhaust device at the highest point, depending on the medium in the catheter, to ensure that the measurement accuracy will not be affected by the accumulation of condensing liquid or gas in the catheter for a considerable period of time.Condensate liquids or gases are discharged periodically.

Four, the use of pressure gauge notes

(1) the instrument shall be installed perpendicular to the horizontal plane;(2) if the measuring point of the instrument is at the same level as the installation of the instrument, whether the correction of additional height error should be considered;(3) the distance between the instrument installation and the measuring point should be as short as possible to avoid indicating delay;(4) ensure the tightness, there should be no leakage phenomenon, especially flammable and explosive gas medium and toxic and harmful medium.

When the instrument is used in the following situations, additional devices shall be added, but additional errors shall not be generated, otherwise correction shall be considered.

(1) in order to ensure that the stainless steel pressure gauge is not affected by the measured medium erosion or viscosity is too large, crystallization, should be installed with isolation device;

(2) in order to ensure that the instrument is not affected by the sharp change of the measured medium or the pulsation pressure, add a buffer.Especially in the pressure surge and pressure drop, the pressure meter is most likely to be damaged and scrapped, or even spring tube crack, leakage phenomenon;

(3) in order to ensure that the instrument is not affected by vibration, the pressure instrument should be equipped with a vibration absorber and a fixed device;

(4) in order to ensure that the meter is not affected by the high temperature of the medium under test, a fluid-filled pipe bending device should be installed;

(5) it is strictly prohibited to use special instruments for special purposes, nor to make measurements without special and reliable devices, nor to use general pressure gauges for pressure measurement of special media;

(6) for the newly purchased pressure measuring instrument, before the installation and use, must carry out measurement verification, in order to prevent vibration, damage or other factors in the transit of the pressure meter to destroy the accuracy.