introduction
Pressure is one of the important process parameters in industrial production. If the pressure does not meet the requirements, it will not only affect production efficiency, reduce product quality, but even cause serious safety accidents. So pressure measurement has a special status in industrial production. This article introduces the selection, installation and calibration of pressure gauges respectively.
First, the choice of pressure gauge
The correct selection of the instrument type according to the product process requirements is an important prerequisite for ensuring the normal operation of the instrument and safe production. Generally, the following three requirements should be considered when selecting the instrument type: (1) Select according to the requirements of the product process in industrial production. For example, whether remote transmission, automatic recording or alarm is required; (2) According to the physical and chemical properties of the measured medium. Such as corrosiveness, temperature, viscosity, degree of contamination, flammable and explosive properties, etc., whether to put forward special requirements for the measuring instrument to choose; (3) According to the on-site environmental conditions. Such as high temperature, electromagnetic field, vibration and on-site installation conditions, etc., whether there are special requirements for the type of instrument, etc.
1. Determination of the measuring range of the instrument
In order to use the instrument reasonably and economically, the range of the instrument cannot be too large, but in order to ensure the measurement accuracy, the minimum value of the measured pressure is generally not less than 1/3 of the full scale of the instrument. The elastic element is permanently deformed due to excessive stress for a long time. The upper limit of the pressure gauge should be higher than the maximum value to be measured (1/2~1/3 of the range), and the margin should be reserved.
2. Selection of instrument accuracy
The accuracy of the instrument is determined according to the maximum measurement error allowed in the production process. It cannot be considered that the higher the accuracy of the instrument, the better. On the premise of meeting the process requirements, the instrument with lower precision, low price and durability should be selected as much as possible. Example of instrument type selection: The outlet pressure range of a compressor is 25~28MPa, and the absolute measurement error should not be greater than 1MPa. The process requires on-site observation and high and low limit alarms. Try to choose a pressure gauge correctly, and point out the model, accuracy and measurement range. The required conditions are: the measured pulsating pressure is 25~28MPa, and the absolute measurement error is less than or equal to 1MPa. Observation, high and low limit alarm. When selecting the instrument, consider that the pulsating pressure has a great influence on the life of the instrument, so the upper limit of the instrument selected is: P1=Pmax*2=28*2=56MPa. If the measurement range of the pressure gauge is 0~60MPa, then: 25MPa/60MPa>1/3, the minimum value of the measured pressure is not less than 1/3 of the full scale, and the lower limit value also meets the requirements. In addition, according to the requirements of measurement error, it can be calculated that the requirements for the allowable error of the instrument are: 1/60*100%=1.67%, so the instrument with an accuracy level of 1.5 can meet the error requirements.
The 2nd. Installation of pressure gauge
Whether the pressure gauge is installed correctly or not directly affects the accuracy of the measurement results and the service life of the pressure gauge. The key to the installation of the pressure gauge is the selection of the pressure measuring point: (1) The pressure measuring point should be selected where the measured medium flows in a straight line. For the pipe segment, do not select it at the bend, bifurcation or dead end of the pipeline. (2) When measuring the liquid pressure, the pressure point should be perpendicular to the flow direction, the inner end face of the pressure pipe should be flush with the inner wall of the equipment, and there should be no protrusions or burrs. (3) When measuring the liquid pressure, the pressure-taking point should be at the lower part of the pipeline, so that no gas is accumulated in the pressure-guiding pipe; when measuring the gas pressure, the pressure-taking point should be above the pipe, so that no liquid is accumulated in the pressure-guiding pipe. (4) A shut-off
The 3rd. Verification and calibration of pressure (differential pressure) detection instruments
Before the instrument can be used, it must be verified and calibrated. Instruments used for a long time should also be checked regularly, and the cycle should be determined according to the frequency of use and the degree of emphasis. When the instrument has a long-distance transmission system and a secondary instrument, it should be verified and calibrated together with the secondary instrument. The method of pressure gauge calibration is: use a standard pressure gauge to calibrate.
