A pressure meter is an instrument that measures and indicates higher than the ambient pressure with an elastic element as a sensitive element. It is widely used in almost all industrial processes and research fields. In the heat pipe network, oil and gas transmission, water supply system, vehicle repair and maintenance shop, and other fields can be seen everywhere. Especially in the control and measurement process, because the elastic sensitive element of mechanical pressure gauge has the characteristics of high mechanical strength and convenient production, the mechanical pressure gauge is widely used.
Selection of pressure gauges should be based on the production process, production requirements, specific analysis of the specific circumstances. Under the premise of meeting the technological requirements, we should consider comprehensively and comprehensively in the light of the principle of economy, and should consider the following aspects:
1, type selection
The selection of instrument type must meet the requirement of process production. For example, whether remote automatic recording or alarm; the nature of the measured medium (such as the temperature of the measured medium height, viscosity, corrosive, flammable and explosive, dirt etc.) whether to put forward special requirements on the instrumentation, on-site environmental conditions (such as temperature, humidity, magnetic field strength and the vibration of the instrument) type etc.. Therefore, according to the requirements of the process, the correct selection of instrument type is an important prerequisite to ensure the normal operation of the instrument and safety in production.
For example, the ordinary pressure gauge spring tube adopts copper alloy (high pressure alloy steel), while ammonia pressure gauge, spring tube materials are used carbon steel (or stainless steel), copper alloy is not allowed. Since ammonia produces chemical reactions with copper, it will explode, so ordinary pressure gauges cannot be used for ammonia pressure measurements.
The oxygen pressure gauge and the ordinary pressure gauge can be exactly the same in structure and material, but oxygen must be banned from the pressure gauge. Because the oil into the oxygen system, easy to cause explosion. When the oxygen pressure gauge is used, the oil can not be used as the working medium as the ordinary pressure gauge, and the oxygen pressure meter shall avoid the oil pollution in the storage. If you have to use the existing oil pressure gauge to measure the oxygen pressure, you must wash it with carbon tetrachloride before use, and check it carefully until the oil free.
2、determine the scope of measurement
In order to ensure that the elastic element can work reliably in the safety range of the elastic deformation, in the table range selection pressure, must according to the size and pressure changes in the measured pressure speed, there is enough room, therefore, the upper limit value should be the maximum pressure may be higher than the value in the production process. According to the provisions of the automatic design of 'chemical technology', in the case of measuring the steady pressure, the maximum working pressure shall not exceed the upper limit value of 2/3 measurement; measurement of fluctuating pressure, the maximum working pressure shall not exceed the upper limit value of 1/2; the measurement of high pressure, the maximum working pressure shall not exceed the upper limit value of 3/5. The minimum measured pressure shall be no less than 1/3 of the upper limit of the instrument measurement. So as to ensure the linear relationship between the output of the instrument and the quantity of the input
According to the maximum and minimum values of the measured parameters, the upper and lower limits of the instrument can be calculated, and the measuring range of the instrument can not be directly taken as the measuring range of the instrument. When we select the upper limit of the scale of the instrument, we should select it in the standard series stipulated by the state. China's pressure gauge measurement 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 or negative).
3、Selection of accuracy grade
According to the maximum absolute error permitted by the process and the best range of the selected instrument, the maximum reference error allowed by the instrument is calculated, and the accuracy of the instrument is determined in the precision grade specified by the state. Generally speaking, the more sophisticated the instrument is, the more accurate and reliable the measurement result is. But you can not believe that the higher the accuracy of the instrument used, because the more sophisticated instruments, the more expensive the general price, the more difficult to operate and maintenance.
Selection example:
1、For the measurement of viscosity or pH and other special medium, should use the diaphragm pressure gauge, stainless steel pipe, stainless steel spring movement, stainless steel shell or bakelite shell.
According to the measurements of different media, on the pressure gauge should be provided the color name, and indicate the special medium, the oxygen table must be marked with red 'no oil', with dark green color under the line of hydrogen, ammonia and so on under the horizontal yellow color.
2、When installing the wall, the pressure gauge with the edge should be used; when the pipe is directly installed on the pipeline, the pressure gauge without edge shall be used; when the gas is measured directly, the pressure gauge with the safety hole at the back of the watch case shall be selected. The diameter of the watch case should be selected from the position of pressure measurement and the convenience of observation management.
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