Measurement around you - pressure gauge measurement knowledge
Pressure plays a very important role in the production and control of industrial automation, and the inaccurate indication of the pressure instrument and the non-compliance with the process requirements will not only affect the production efficiency of the enterprise, but also affect the product quality, and more importantly, it will even cause safety production accidents. Today, let's talk about some measurement tips about pressure gauges.
1. Overview of pressure gauges
(1) What is a pressure gauge.
A pressure gauge is a gauge that is used to measure greater than atmospheric pressure based on atmospheric pressure. It is mainly used for pressure measurement of liquids, gases and steames. What we see in daily life is the elastic element pressure gauge, which uses sensitive elements (such as spring tubes) to produce elastic deformation under the action of pressure, and the magnitude of the deformation is in a certain linear relationship with the pressure of the action, which is amplified by the transmission mechanism, and the measured pressure is indicated by the pointer on the index plate. According to the use and special needs, the pressure gauge can be divided into ordinary pressure gauge, oxygen pressure gauge, electric contact pressure gauge, remote pressure gauge, vibration resistant pressure gauge, double needle double tube or double needle single tube pressure gauge, digital display pressure gauge, digital precision pressure gauge, etc.
(2) The composition of the general pressure gauge
Generally, the pressure gauge is mainly composed of the following parts: joints, spring tubes, sealing sheets, movements, connecting rods, dials, hands, liners, cases, glasses, and rings. The key components are the joints, the spring tubes and the movement.
(3) The working principle of the general pressure gauge.
The working principle of the general pressure gauge is: under the action of pressure and vacuum, the spring tube produces elastic deformation and causes the displacement of the end of the tube, and its displacement is amplified by the mechanical transmission mechanism (connecting rod and movement), transmitted to the indication device, and then the pressure or vacuum value is deflected by the pointer on the dial.
(4) The use of pressure gauges.
The main uses of pressure gauges are as follows:
1. Monitor the operation of the pressurized vessel or the working medium in the pipeline in order to properly control the pressurized vessel and protect the safety of production equipment.
2. Understand the state of material changes in the production process, so that some process parameters are controlled under specified conditions to ensure that the product quality meets the specified requirements.
3. By mastering the pressure parameters, it provides a reliable basis for operators to monitor and regulate production.
(5) Advantages of general pressure gauges.
General pressure gauges have the following advantages:
1. Simple structure, reliable and durable, easy to use and maintain.
2. Small appearance, light weight, wide measurement range, obvious indication, direct reading.
3. There is sufficient accuracy and good stability of the indication value.
4. Low price.
2. Compulsory verification of measuring instruments
According to the Catalogue of Measuring Instruments for the Implementation of Compulsory Management issued by the State Administration for Market Regulation, the pressure instruments and pressure instruments used by each unit are divided into compulsory verification and non-compulsory verification. According to the above announcement, the following working measuring instruments and pressure instruments in use belong to the compulsory verification scope for safety protection:
1. Measurement of the main gas drum and feedwater pressure of the power station boiler;
2. Measurement of the pressure of the air chamber and main pipe of the fixed air compressor;
3. Measurement of oil pressure and locomotive pressure of generator and gas turbine;
4. Measurement of pressure with alarm device;
5. Measurement of pressure of sealed pressurized vessels;
6. Measurement of pressure of harmful, toxic and corrosive medium.
The pressure gauge of other working measuring instruments that do not fall within the scope of the announcement will no longer be subject to compulsory verification, and the user can choose the method of non-compulsory verification or calibration to ensure the accuracy of the measurement.
3. Measurement verification of pressure gauge
For pressure tables listed in the compulsory verification catalog, users should log on to the "China Electronic Quality Supervision (e-CQS) Public Service Portal" to apply for compulsory verification. The measurement verification of general pressure gauges implements JJG52-2013 "Verification Regulations for Elastic Element General Pressure Gauges, Pressure Vacuum Gauges and Vacuum Gauges", and the verification items include appearance, zero error, indication error, return error, tapping displacement and pointer deflection stability. After passing the verification of the pressure gauge, the metrology verification personnel will post the verification mark on the pressure gauge and issue the verification certificate. The pressure gauge shall be put into use only after passing the verification and obtaining the verification certificate, and shall not be used without verification or unqualified verification. The mandatory verification period of the pressure gauge is 6 months.
The model of the verification certificate of the market supervision, inspection and testing information center of Zhungeer Banner (the style of the certificate of the legal metrology verification agency in various regions is different)
Fourth, the choice of pressure gauge
The selection of the pressure gauge should be determined according to the nature of the medium to be measured, the rated working pressure, the accuracy level requirements of the process production, the environmental conditions of the installation location, and whether there are special requirements such as corrosion resistance, shock resistance and explosion resistance. The rated working pressure of the medium to be measured should be between 1/3 and 2/3 of the gauge range.
5. Precautions for the use of pressure gauges
When using pressure, the following should be noted:
(1) Regular inspection. Check that the needle of the gauge rotates and fluctuates normally, keep the gauge clean, and make sure that the glass on the dial is bright and clear so that the pressure value can be read.
(2) Connecting pipe maintenance. Regularly blow the connecting pipe of the pressure gauge to prevent clogging.
(3) Verification/calibration. Regular calibration of the pressure gauge, mandatory verification of the pressure gauge should be strictly implemented every 6 months verification cycle, non-compulsory verification of the pressure gauge user should be based on the use of the pressure gauge environment, media, etc. to develop a verification and calibration plan, it is recommended to carry out at least once a year to maintain the accuracy of measurement.
(4) Avoid over-range use. Make sure that the range of the gauge is suitable for the pressure range tested, and avoid exceeding the range to prevent damage.
(5) Use environment. Use the pressure gauge in a dry, clean, and well-ventilated environment to avoid the effects of pollutants such as moisture, dust, and grease. At the same time, environments that are too humid, high or low temperature should be avoided.
(6) Maintenance. Perform regular cleaning and maintenance, use warm water and soap or special detergents to clean and avoid using too much greasy, thick soot and other contaminants.
(7) Avoid vibration and impact. Handle the gauge with care and avoid severe vibrations and impacts, which may affect its accuracy or cause damage.
Contributed by Liu Lu
Editor: Qin Jiayao
Proofreader: Liu Xiaoyu
Review: Diao Haiqian