Anhui Star Control Instrument Co., Ltd.

Anhui Star Control Instrument Co., Ltd.

Pressure gauge selection principle

The selection of pressure gauges should be based on the production process requirements, and specific analysis should be made for specific conditions. Under the premise of meeting the process requirements, comprehensive and comprehensive consideration should be made on the principle of economy. Generally, the following issues should be considered:
1, the choice of type
The choice of instrument type must meet the requirements of process production.
The properties of the measured medium (such as the temperature of the measured medium, the viscosity, the corrosion, the degree of contamination, whether it is flammable or explosive, etc.), or whether special requirements are placed on the instrument, and the on-site environmental conditions (such as humidity, temperature, magnetic field strength, Vibration, etc.) Requirements for instrument types etc. Therefore, the correct selection of instrument type according to the process requirements is an important prerequisite for the normal operation of the instrument and safe production.
For example, spring tubes for common pressure gauges use copper alloys (high-pressure alloy steels), and ammonia pressure gauge spring tube materials use carbon steel (or stainless steel), which does not allow copper alloys. Because ammonia and copper react chemically and explode, ordinary pressure gauges cannot be used for ammonia pressure measurements.
Oxygen pressure gauges and ordinary pressure gauges can be identical in structure and material, except that oxygen pressure gauges must be banned from oil. Because the oil into the human oxygen system can cause explosions. Oxygen pressure gauges used in the calibration can not use oil as working medium like ordinary pressure gauges, and oxygen pressure gauges should strictly avoid contact with oil during storage. If it is necessary to measure the oxygen pressure using an existing oil pressure gauge, it must be cleaned with carbon tetrachloride repeatedly before use and carefully checked until there is no oil.
2, the determination of the measurement range
In order to ensure that the elastic element can work reliably within the safe range of elastic deformation, when selecting the pressure gauge range, it must be based on the size of the measured pressure and the speed of the pressure change, leaving enough room, therefore, the upper limit of the pressure gauge Should be higher than the maximum pressure possible in process production. According to the “Technical Regulations for Chemical Industry Automation Design”, the maximum working pressure shall not exceed 2/3 of the upper limit of the measurement when measuring the stable pressure; the maximum working pressure shall not exceed 1/2 of the upper limit of the measurement when the pulsating pressure is measured; When measuring high pressures, the maximum working pressure should not exceed 3/5 of the upper measuring limit. The minimum value of the general measured pressure should not be less than 1/3 of the upper limit of the instrument's measurement. In order to ensure the linear relationship between the output and input of the meter
According to the maximum value and minimum value of the measured parameter, the upper and lower limits of the instrument can be calculated and the measurement range of the instrument can not be directly used as this value. When we select the upper limit of the scale of the instrument, we should select it from the national standard series. China's standard range of pressure gauge measurement range: -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, the choice of accuracy level
According to the maximum absolute error allowed for process production and the selected instrument range, the maximum allowable citation error of the instrument is calculated, and the accuracy of the instrument is determined in the national precision level. In general, the more precise the selected instrument, the more accurate and reliable the measurement results. However, it cannot be considered that the higher the accuracy of the selected instrument, the better, because the more sophisticated the instrument is, the more expensive it is and the more troublesome it is to operate and maintain.
For example:
1. For measuring viscous or acid-base and other special media, diaphragm pressure gauge, stainless steel spring tube, stainless steel movement, stainless steel shell or bakelite shell should be selected.
According to the measured medium, there should be a specified color scale on the pressure gauge, and the name of the special medium should be noted. The oxygen table must be marked with the word “Red oil” and the hydrogen gas should be marked with a dark green horizontal line. Yellow horizontal stripes and so on.
2. When installing against a wall, use a pressure gauge with an edge. When directly installed on the pipeline, use a pressure gauge with no edge. When measuring gas directly, use a pressure gauge with a safety hole behind the case. Due to the pressure measurement position and ease of observation management considerations, the size of the case diameter should be selected.
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