The selection of pressure gauges should be based on the use of process production requirements, specific circumstances to do a specific analysis.
In the premise of meeting the requirements of the process, should be based on the principle of saving comprehensive and comprehensive consideration, generally consider the following aspects of the problem:
1, the type of selection The choice of instrument type must meet the requirements of process production. For example, whether remote transmission, automatic recording or alarm, the nature of the medium being measured (such as the temperature of the medium under test, viscosity, corrosive, dirty degree, whether flammable and explosive, etc.) whether the instrument to make special requirements, on-site environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) to the instrument type requirements.
Therefore, the correct selection of instrument type according to the process requirements is an important precondition to ensure the normal work and safe production of the instrument. For example, the ordinary pressure gauge of the spring tube is more copper alloy (high-pressure alloy steel), and ammonia pressure gauge spring tube materials are used carbon steel (or stainless steel), do not allow the use of copper alloy.
Because ammonia reacts with copper, it explodes, so the normal pressure gauge cannot be used for ammonia pressure measurement. The oxygen pressure gauge and the ordinary pressure gauge in the structure and material can be exactly the same, just oxygen pressure gauge must be forbidden oil. Because the oil into the human oxygen system easily cause explosion. The oxygen pressure gauge used in the calibration, can not be used as the normal pressure gauge oil as a working medium, and oxygen pressure gauge in storage to strictly avoid contact with oil.
If the existing oil pressure gauges must be used to measure the oxygen pressure, before use must be repeated cleaning with carbon tetrachloride, carefully check until the oil-free.
2. Determination of measuring range In order to ensure that the elastic element can work reliably in the safe range of elastic deformation, in selecting the pressure gauge range, the pressure must be measured according to the size and speed of the pressure change, leaving enough room, therefore, the upper limit of the pressure gauge should be higher than the maximum possible pressure value in the process production. According to the "Chemical Control Design Technology Regulations", in the measurement of stable pressure, the maximum operating pressure should not exceed the measurement limit of 2/3; when measuring fluctuating pressure, the maximum working pressure should not exceed the measurement limit of 1/2; when measuring high pressure, the maximum working pressure should not exceed 3/5 of the measurement upper limit value. The minimum value of the measured pressure shall be no less than 1/3 of the upper limit of the instrument measurement.
Thus, the linear relationship between the output of the instrument and the quantity of the transmission is ensured. The upper and lower limits of the instrument are calculated according to the maximum and minimum values of the measured parameters, and cannot be used as the measuring range of the meter directly. When selecting the upper limit of the gauge, we should select it in the National standard series.
China pressure gauge measuring range Standard series are: -0.1-0.06,0.15;0-1,1.6,2.5,4,6,10x10 "MPa (where n is a natural integer. Can be positive, negative).
3. Selection of accuracy level The accuracy of the instrument is determined in the state-specified accuracy class according to the maximum absolute error allowable by the process and the maximum range of the selected instrument, and the largest allowable reference error of the instrument. In general, the more sophisticated the instrument, the more accurate and reliable the measurement results.
But it cannot be considered that the higher the precision of the instrument, the better, because the more sophisticated the general price of the more expensive, operation and maintenance more trouble.
1, for the measurement of viscous or acid and alkali and other special media, you should choose diaphragm pressure gauge, stainless steel spring tube, stainless steel movement, stainless steel shell or bakelite shell.
According to the medium, the pressure gauge should have the specified color standard, and the name of the special medium, the oxygen meter must be marked with red "forbidden oil", hydrogen with dark green Line color standard, ammonia with yellow line color standard and so on. 2, against the wall installation, the use of the edge of the pressure gauge, directly installed in the pipeline, the use of non-edge pressure gauges should be used for the direct measurement of gas, the case should be selected with a safety hole behind the pressure gauge.
The size of the case diameter should be chosen for the purpose of measuring the pressure position and for easy observation management.
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