Pressure gauge (English name: pressure gauge) refers to the elastic element as a sensitive element, measuring and indicating higher than the ambient pressure of the instrument, the set of extremely common, it is almost all over the industrial process and scientific research areas. In the heat pipe network, oil and gas transmission, water and gas supply systems, vehicle maintenance stores and other fields can be found everywhere. Especially in the industrial process control and technology measurement process, due to the mechanical pressure gauge of the elastic sensitive element has a high mechanical strength and production convenience and other characteristics, so that the mechanical pressure gauge has been more and more widely used set.
Basic introduction Chinese name ：pressure gauge Foreign name ：pressure gauge Role ：Measurement and indication of higher than the ambient pressure of the instrument Industry ：Industry Principle of work, the main structure, the use of attention, selection principles, the main classification, the basic terminology, the common type, the installation, the upper limit of the measurement, the quality requirements, the range of choice, the accuracy of the level of overhaul and maintenance, the common problems, corrosion measures, the main principle of work, the main structure of the pressure gauge, use of attention, selection principles, main classification, basic terminology, common types, installation, measuring upper limit, quality requirements, range selection, accuracy class, repair and maintenance, common problems, corrosion measures, the principle of work of the gauge Principle of operation Pressure gauge through the table of the sensitive components (Borden tube, membrane box, bellows) of the elastic deformation, and then by the table movement of the conversion mechanism will be the pressure of deformation conduction to the pointer, caused by the pointer to rotate to display the pressure. Main structure Overflow hole: In case of an emergency situation where the bourdon tube bursts, the internal pressure will be released to the outside world through the overflow hole to prevent the glass panel from bursting. Note: In order to maintain the normal performance of the overflow hole, it is necessary to leave at least 10mm of space behind the gauge, and not to modify or plug the overflow hole. Pressure Gauge (Figure 8) Pointer: In addition to the standard pointer, other pointers are optional. Glass panel: In addition to the standard glass, other special material glass, such as reinforced glass, non-reflective glass is also optional. Performance classification: General type (standard), general type for steam (M), heat-resistant type (H), vibration-resistant type (V), vibration-resistant type for steam (MV) heat-resistant vibration-resistant type (HV). Treatment: No oil/water treatment Water or oil residue in the liquid-access portion is removed at the time of manufacture. Exterior designation: Case color other than standard color to be specified. Throttle (optional): To minimize pulsating pressure, the throttle is installed at the pressure inlet. Attention to the use of 1, the instrument must be vertical: the installation should be used 17mm wrench screwed tight, should not be strong twisting case; transport should be avoided collision; Pressure gauge (Figure 5) 2, the instrument should be used in the surrounding ambient temperature of -25 ~ 55 ℃; 3, the use of the working environment vibration frequency & lt; 25HZ, amplitude is not greater than 1mm; 4, the use of the meter due to the 4, in use because of the high ambient temperature, the instrument indicator value does not return to zero or show value overshoot, can be case upper sealing rubber plug cut open, so that the instrument cavity and the atmosphere can be communicated; 5, the instrument should be used in the upper limit of the range of 1/3 ~ 2/3; 6, in the measurement of corrosive media, may be crystalline media, viscosity of the media should be added isolation device; 7, the instrument should be frequently calibrated (at least once every three months), if found faults should be repaired in a timely manner; 8, the instrument should be used in a timely manner, if found faults should be repaired; 7, the instrument should be frequently calibrated (at least once every three months). If a failure is found should be repaired in a timely manner; 8, instrumentation from the date of shipment, within six months if found under normal storage and use conditions due to poor manufacturing quality failure or damage, the company is responsible for the repair or replacement; 9, the need to measure corrosive media instrumentation, the requirements of the conditions should be specified at the time of ordering. Selection principles The selection of pressure gauges should be based on the use of technology production requirements, for specific situations to do specific analysis. Under the premise of meeting process requirements, should be based on the principle of saving comprehensive consideration, generally should consider the following aspects of the problem: 1, the type of selection Instrument type selection must meet the requirements of the process. For example, whether the need for remote transmission, automatic recording or alarm; the nature of the measured medium (such as the measured medium temperature, viscosity, corrosivity, dirt, whether flammable and explosive, etc.) whether the instrumentation to put forward special requirements, the scene of environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) on the type of instrumentation requirements. Therefore, according to the process requirements to correctly select the type of instrumentation is to ensure the normal operation of the instrument and the important premise of safe production. Pressure gauge (Figure 2) For example, ordinary pressure gauge spring tube more copper alloy (high-pressure alloy steel), while the ammonia pressure gauge spring tube materials are used in carbon steel (or stainless steel), do not allow the use of copper alloy. Because ammonia and copper chemical reaction, will explode, so the ordinary pressure gauge can not be used for ammonia pressure measurement. Oxygen pressure gauge and ordinary pressure gauge in the structure and material can be exactly the same, just oxygen pressure gauge must be prohibited oil. Because oil into the oxygen system is easy to cause an explosion. Oxygen pressure gauge used in the calibration, can not be used as ordinary pressure gauge as oil as the working medium, and oxygen pressure gauge in storage to strictly avoid contact with oil. If you must use the existing pressure gauge with oil to measure the oxygen pressure, you must use carbon tetrachloride to clean it repeatedly before use, and carefully check until there is no oil. 2, the determination of the measuring range In order to ensure that the elastic element can work reliably in the elastic deformation of the safety range, in the selection of the pressure gauge range, must be based on the size of the measured pressure and pressure change quickly, leaving enough room, therefore, the upper limit of the pressure gauge should be higher than the maximum possible pressure value of the process production. According to the "chemical automatic control design technical regulations", in the measurement of stable pressure, the maximum working pressure should not exceed 2/3 of the upper limit of measurement; measurement of pulsating pressure, the maximum working pressure should not exceed 1/2 of the upper limit of measurement; measurement of high-pressure, the maximum working pressure should not exceed 3/5 of the upper limit of measurement. The minimum value of the measured pressure should not be less than 1/3 of the upper limit of the instrument measurement, thus ensuring that the output of the instrument and the linear relationship between the output Pressure Gauge (Figure 3) According to the maximum value of the measured parameters and the minimum value of the instrument to calculate the upper and lower limits, can not be directly as the instrument's range of measurement of this value. We choose the upper limit of the scale of the instrument, should be selected in the national standard series. China's standard series of pressure gauge measuring range: -0.1-0.06, 0.15; 0-1, 1.6, 2.5, 4, 6, 10X10" MPa (which n is a natural integer. (Can be positive or negative). 3, the selection of precision level according to the process of production allows the maximum absolute error and the selected instrumentation of the most range, calculate the maximum quoted error allowed by the instrumentation, in the national provisions of the precision level to determine the accuracy of the instrument. Generally speaking, the more precise the selected instrument, the more accurate and reliable the measurement results. However, we cannot assume that the higher the precision of the selected instrument, the better, because the more precise the instrument is generally more expensive, the operation and maintenance of the more laborious. Examples: 1, for the measurement of viscous or acidic and alkaline and other special media, should be selected diaphragm pressure gauge, stainless steel spring tube, stainless steel movement, stainless steel shell or wood shell. Pressure gauge (Figure 4) according to the different media measured, the pressure gauge should be specified on the color code, and indicate the name of the special media, oxygen table must be marked with red "no oil" words, hydrogen with dark green under the horizontal line of the color code, ammonia with a yellow under the horizontal line of the color code and so on. 2, installed against the wall, should be used with the edge of the pressure gauge; directly installed in the pipeline, should be used without the edge of the pressure gauge; for direct measurement of gas, should be used behind the case with a safety hole pressure gauge. The size of the case diameter should be selected for the consideration of pressure measurement position and easy observation and management. There are many types of pressure gauges, which not only have general (ordinary) pointer indication type, but also digital type; not only conventional type, but also special type; not only contact type, but also remote transmission type; not only vibration-resistant type, but also anti-vibration type; not only diaphragm type, but also corrosion-resistant type and so on. Pressure gauge series is complete. It is not only a conventional series, there are digital series; not only ordinary media set series, there are special media set series; not only switch signal series, there are remote signal series, etc., they are derived from the practice of demand, has constituted a complete series. The specifications and models of pressure gauge are complete, and the structure type is perfect. In terms of nominal diameter, there are Φ40mm, Φ50mm, Φ60mm, Φ75mm, Φ100mm, Φ150mm, Φ200mm, Φ250mm and so on. From the installation structure type, there are direct mounting type, embedded type and convex mounting type, in which embedded type is divided into radial embedded type and axial embedded type, and convex mounting type is also divided into radial convex mounting type and axial convex mounting type. Direct mounting type, which is divided into radial direct mounting type and axial direct mounting type. Radial direct mounting is the basic installation type, generally in the installation structure is not specified when the type, are referred to as radial direct mounting. Axial direct mounting type to consider the stability of its own support, generally only in the nominal diameter of less than 150mm on the pressure gauge is selected. The so-called embedded and convex mounted pressure gauge, is often referred to as the edge (mounting ring) pressure gauge. Axial embedded both axial forward with edge, radial embedded means radial front with edge, radial convex mounted (also called wall mounted) means radial back with edge pressure gauge. From the range and range segments, in the positive pressure range is divided into micro-pressure range segments, low-pressure range segments, medium-pressure range segments, high-pressure range segments, ultra-high-pressure range segments, each range segment is subdivided into a number of types of measurement ranges (instrument ranges); in the negative pressure range (vacuum) and there are three types of negative pressure (vacuum gauge); positive pressure and negative pressure range pressure gauge is a cross-range pressure gauge. Its standardized name for the pressure vacuum gauge, also called vacuum pressure gauge. It can not only measure the positive pressure pressure, but also can measure the negative pressure pressure. The classification of the accuracy level of the pressure gauge is very clear. Common accuracy levels are 4, 2.5, 1.6, 1, 0.4, 0.25, 0.16, 0.1 and so on. The accuracy level should be marked on the dial, and there are corresponding regulations for its marking, such as "①" means that its accuracy level is 1. For some of the accuracy level is very low pressure gauge, such as 4 level, and some do not need to measure the exact pressure value, only need to indicate the pressure range, such as fire extinguishers on the pressure gauge, you can not identify the accuracy level. Pressure gauge according to its measurement accuracy: can be divided into precision pressure gauge, general pressure gauge. Precision pressure gauge measurement accuracy level were 0.1, 0.16, 0.25, 0.4 0.05 level; general pressure gauge measurement accuracy level were 1.0, 1.6, 2.5, 4. 0 level. Pressure gauge according to its measurement benchmark: Pressure gauge according to its indication of the pressure of different benchmarks, divided into general pressure gauge, absolute pressure gauge stainless steel pressure gauge, differential pressure gauge. General pressure gauge to atmospheric pressure as a reference; absolute pressure gauge to absolute pressure zero as a reference; differential pressure gauge to measure the difference between the two measured pressure. Pressure gauge (Figure 6) Pressure gauge according to its measurement range: Subdivision for the vacuum gauge, pressure vacuum gauge, micro-pressure gauge, low-pressure gauge, medium-pressure gauge and high-pressure gauge. Vacuum gauge is used to measure the pressure value less than atmospheric pressure; pressure vacuum gauge is used to measure the pressure value less than and greater than atmospheric pressure; micro-pressure gauge is used to measure the pressure value less than 60,000 Pa; low-pressure gauge is used to measure the pressure value of 0~6MPa; medium-pressure gauge is used to measure the pressure value of 10~60MPa; Pressure gauges according to the way they are displayed: Pointer pressure gauge, digital pressure gauge. Pressure gauge according to its display: divided into pointer pressure gauge, digital pressure gauge. Pressure gauge according to its function: Pressure gauge according to its different functions can be divided into on-site indication type pressure gauge and with electrical signal control type pressure gauge. General pressure gauge, vacuum pressure gauge, seismic pressure gauge, stainless steel pressure gauge belongs to the local indication type pressure gauge, in addition to the indication of pressure without other control functions. With electrical signal control type pressure gauge output signals are: 1, switching signals (such as electric contact pressure gauge) 2, resistance signals (such as resistance remote pressure gauge) 3, current signals (such as inductive pressure transmitter, remote pressure gauge, pressure transmitter, etc.) Pressure gauges can be divided into different characteristics of the measurement medium: 1, general type pressure gauge: general type pressure gauge for measuring Non-explosive, non-crystallizing, non-condensing copper and copper alloy corrosion-free liquid, gas or steam pressure; 2, corrosion-resistant pressure gauge: corrosion-resistant pressure gauge is used to measure the pressure of corrosive media, commonly used stainless steel pressure gauge, diaphragm-type pressure gauge, etc.; 3, explosion-proof pressure gauge: explosion-proof pressure gauge is used in the environment of explosive mixtures of hazardous places, such as explosion-proof electrical contact pressure gauge, explosion-proof transmitter, etc. 4, special pressure gauge. According to the use of the pressure gauge: can be divided into ordinary pressure gauge, ammonia pressure gauge, oxygen pressure gauge, electric contact pressure gauge, remote pressure gauge, vibration-resistant pressure gauge, with inspection pointer pressure gauge, double needle double tube or double needle single tube pressure gauge, digital pressure gauge, digital precision pressure gauge. Basic terms 1, positive pressure and negative pressure 2, relative pressure and absolute pressure 3, vacuum 4, the pressure is expressed in two ways Pressure is expressed: one is the absolute vacuum as the benchmark pressure, known as the absolute pressure; the other is the atmospheric pressure as the benchmark pressure, known as the relative pressure. Because most of the pressure measuring instruments measured pressure is relative pressure, so the relative pressure is also known as gauge pressure. When the absolute pressure is less than the atmospheric pressure, the absolute pressure inside the container can be less than the value of an atmosphere to indicate. Known as "vacuum". Their relationship is as follows: Absolute pressure = atmospheric pressure + relative pressure Vacuum = atmospheric pressure - absolute pressure China's legal unit of pressure Pa (N / m2), known as the Pascal, or Pascal. Because this unit is too small, it is often used 10^6 times the unit MPa (megapascals). Common types Borden tube pressure gauge: Borden tube sensitive element is bent into a circle, the cross-sectional area of the oval elastic C-shaped tube. The pressure of the measuring medium acts on the inside of the fluctuating tube, so that the elliptical cross-section of the Borden tube tends to the circular cross-section. Due to the small deformation of the Borden tube, a certain ring stress is formed. This ring stress causes the Borden tube to extend outwards. Since the head of the elastic Borden tube is not fixed, a small deformation occurs, the size of which depends on the pressure of the measuring medium. The deformation of the Borden tube is indirectly indicated by the pointer of the measuring medium through the movement. Pressure gauge (Figure 10) Diaphragm box pressure gauge: The diaphragm box sensitive element consists of two pieces of diaphragm connected together to show a circular wave. The pressure of the measuring medium acts on the inside of the diaphragm chamber, and the resulting deformation can be used to indirectly measure the medium's pressure. The magnitude of the pressure value is indicated by a pointer. Membrane box pressure gauge is generally used to measure the pressure of the gas, and can measure micro-pressure, overpressure protection to a certain extent is also possible. When several membrane box sensitive elements stacked together will produce a large transfer force to measure the very small pressure. Explosion-proof pressure gauge: Explosion-proof pressure gauge suitable for use in flammable and explosive occasions, it is different from the ordinary pressure gauge, explosion-proof pressure gauge is more demanding, first of all, the safety factor is high or not, explosion-proof pressure gauge is a lot of kinds of pressure gauges, how to choose the right pressure gauge for you, it is necessary to consider the whole picture. Explosion-proof pressure gauge according to the explosion-proof coefficient: intrinsically safe explosion-proof pressure gauge and explosion-proof pressure gauge. Safety performance points: electric contact explosion-proof pressure gauge, pointer explosion-proof pressure gauge, digital display explosion-proof pressure gauge. Explosion-proof electric contact pressure gauge: Explosion-proof electric contact pressure gauge explosion-proof shell has a good performance of explosion-proof, so the explosion-proof electric contact pressure gauge in the normal course of work due to the impact of sparks or arcs, in addition to withstand the shell inside the explosive gas mixture in the case of once caused by the explosion of explosive pressure, and can effectively prevent the resulting heat to the outside! smooth propagation, but only inside the shell along the explosion-proof joints of the tiny gaps in the slow diffusion to the outside. At this time, the instantaneous temperature transmitted to the outside of the shell has been reduced to the ignition temperature of explosive gas mixtures below, so it will not lead to the explosion. Explosion-proof digital (pointer) display pressure gauge: high accuracy, high stability, error ≤ 1%, internal power supply, micro-power consumption, stainless steel shell, solid protection, beautiful and exquisite. Explosion-proof digital display pressure gauge is widely used in petroleum, chemical, metallurgy, power station and other industrial sectors or electromechanical equipment supporting the measurement of the explosion risk of a variety of fluid media pressure. Vacuum pressure gauge: Vacuum pressure gauge is used to measure the steel, copper and copper alloy non-corrosive, non-explosive risk of non-crystallization, non-condensable liquids, gases or steam medium pressure or negative pressure. Shock-resistant vacuum pressure gauge table for vibration and pressure fluctuations, measurement of non-corrosive, non-crystallization of the negative pressure of the medium. Electric contact pressure vacuum gauge and electric contact vacuum gauge for copper and copper alloy corrosion, no explosion risk of non-crystallization, non-condensable liquids, gases and other media (pressure) and negative pressure measurement, when the pressure reaches a predetermined value, with the help of contact device, can be connected or disconnected from the control circuit, and at the same time send out an electrical signal. Classification of vacuum pressure gauge: vacuum pressure gauge is to atmospheric pressure as a reference, for measuring greater than and less than atmospheric pressure instrument. Pressure gauge (Figure 12) Shock-resistant vacuum pressure gauge as a classification of shock-resistant pressure gauge, used for vibration and pressure fluctuations, measuring the negative pressure of non-corrosive, non-crystalline media. Electric contact vacuum pressure gauge and electric contact vacuum gauge copper and copper alloy without corrosive effect, no danger of explosion of non-crystalline non-condensing liquid, gas and other media (pressure) and negative pressure. Stainless steel pressure vacuum gauge is used to measure the pressure and negative pressure of liquid, gas media without corrosive effect on stainless steel 316, 316L and 0Crl8Ni12MO2Ti, all stainless steel has stronger corrosion resistance to the environment. Acid Resistant Pressure Vacuum Gauge is used to measure the pressure and negative pressure of nitric acid and alkali liquid medium; Acid Resistant Vacuum Gauge is used to measure the negative pressure of nitric acid and alkali liquid. Installation mode Pressure gauge national standard "General Pressure Gauge" GB/T1226-2001 in the 4.1.2 instrumentation according to the threaded joints and installation methods are divided into: direct installation of pressure gauges, embedded (disk mounted) pressure gauges, convex mounted (wall mounted) pressure gauge. Pressure gauge (Figure 13) 1, the installation of the pressure gauge should be installed in accordance with the requirements of the state of installation, the dial should not be placed horizontally, the height of the installation position should be easy for staff to observe. 2, the pressure gauge installation and the distance between the pressure point should be as short as possible, to ensure that the integrity of the seal, can not appear leakage phenomenon. 3, in the installation of the front of the pressure gauge should be a buffer; in order to facilitate the inspection, in the instrument should be equipped with a cut-off valve below; when the medium is dirty or pulse pressure, filters, buffers and stabilizer gas can be used. Measurement of the upper limit 1, the size of the upper limit of the pressure gauge measurement is based on the spring tube size, stiffness and non-linear conditions of the design, the upper limit of the measurement of the value of 1 × 10n, 1.6 × 10n, 2.5 × 10n, 4 × 10n, 6 × 10n five series, n is a positive integer, negative integer or zero. Pressure gauge (Figure 14) 2, digital pressure gauge pressure range: -100kPa ～ 2kPa ～ 260MPa. 3, the pressure gauge is lower than 1/3 range part of the accuracy is low, should not be used. Select the upper limit of measurement, in order to ensure that the pressure gauge to work safely and reliably, to maintain its service life, generally should be greater than 1/3 of the maximum operating pressure. 4, select the use of the range, according to the universality of the load condition, should be selected to use the full range of 1 / 3 ~ 2 / 3 is appropriate, because of the use of this range of higher accuracy, and in the smooth, fluctuating two kinds of loads can be used. The maximum range of use shall not exceed 3/4 of the full scale of the dial. Quality requirements 1, the general pressure gauge spring tube is a certain cross-sectional shape (commonly used flat round and nearly oval two kinds), bent into a "C" shape, and can meet certain elasticity requirements of the tubular spring. If the spring tube is too small, it will affect the accuracy level of the pressure gauge. pressure gauge (Figure 16) 2, the pressure gauge value more than the permissible error, it should be adjusted to repair the table value adjusting screw, if the table does not show the value of the adjusting screw, the table can only be judged as unqualified. 3, pressure gauge dial index numbers and symbols should be complete and clear. Dial index scale should be evenly distributed, the center angle of the package is generally 270 °, the pressure gauge pointer should be extended into all the index line, the width of the pointer indicator end should not be greater than 1/5 of the minimum index interval. the distance between the pointer and the dial plane should be in the range of 1 ~ 3mm case outside diameter of more than 200mm (including 200mm), the pointer and the dial plane distance should be in the range of 2 ~ 4mm. The distance between the pointer and the plane of the indexing dial shall be within the range of 2-4mm. 4. For pressure gauge with stop pin, the pointer should be close to the stop pin when there is no pressure or vacuum, and the "shrinkage" should not exceed the permissible error. 5, the pressure gauge case should be able to protect the internal components from contamination, the pressure gauge should be equipped with safety holes, safety holes on the need for dust-proof devices. 6, digital pressure gauge should look at the overall structure of the rationality of the material selected, the aging process of electronic components, long-term stability. Range selection 1, in order to ensure that the pressure gauge elastic element can work reliably within the safety range of elastic deformation, the choice of pressure gauge range should not only be based on the size of the measured pressure, but also should take into account the speed of change of the measured pressure, the range needs to leave enough room. When using the pressure gauge to measure the steady pressure, the maximum working pressure should not exceed 2/3 of the range; 2. When using the pressure gauge to measure the pulsating pressure, the maximum working pressure should not exceed 1/2 of the range; 3. When using the pressure gauge to measure the high pressure, the maximum working pressure should not exceed 3/5 of the range; in order to ensure the accuracy of the measurement, the minimum working pressure should not be less than 1/3 of the range; in accordance with this principle, the pressure gauge should be selected according to the maximum pressure under test. According to this principle, after calculating a value according to the maximum pressure to be measured, select a measurement range slightly larger than this value from the catalog of pressure gauges. 4, should be selected according to the boiler working pressure, the limit value of the range scale should be 1.5 ~ 3.0 times the working pressure, preferably 2 times. In industrial boilers, the actual situation is that the actual operation of the boiler working pressure is always lower than the rated pressure on the nameplate, industrial steam boilers and hot water heating boilers are so. For example, 4t / h of steam boilers, rated pressure of 1MPa, manufacturers such as 1.5 times to be equipped with pressure gauges, should be equipped with 1.6MPa range pressure gauge. If the user needs due to the production process, the actual operation of the 0.5MPa pressure that can meet the process requirements, then run the range, the pressure gauge pointer in the range of less than one-third of the position, the pointer turned over a small angle. That is, the selection of the pressure gauge range is too large. Hot water boiler is also the case, such as heating boiler rated pressure of 0.7MPa, equipped with a pressure gauge should be 1MPa or 1.6MPa, such as equipped with a 1MPa pressure gauge, for fear of overloading the pressure gauge in the hydrostatic test, so they are equipped with a range of 1.6MPa pressure gauge. Actual operation, as long as 0.2MPa can meet the heating requirements, the pressure gauge pointer in the range of one-eighth of the position, it is difficult to make people believe that the accuracy and sensitivity of the pressure gauge. 5, in order to solve the above problems, two pressure gauges should be used, that is, in the hydrostatic test, the boiler factory is equipped with the pressure gauge according to the rated pressure; 6, in the daily operation of the actual working pressure of two times to be equipped with pressure gauges. If the working pressure is 0.2MPa, that is, with a 0.4MPa range of pressure gauge. So that the pointer in the middle of the dial position, vertical up. The starting pressure of the safety valve is also adjusted according to the working pressure, the pressure gauge still has enough margin to cope with the overpressure indication. Accuracy level 1, the accuracy level of the pressure gauge is to reflect the accuracy of the tested table and precision table for comparison, the indication value and the real value close to the degree of accuracy. It is equal to the absolute value of the maximum basic error and the upper limit of the measurement of the ratio of the percentage, is based on the calibration of the size of the error to determine. Pressure gauge (Figure 15) 2, China's general industrial pressure gauge *** divided into four accuracy levels, in line with the JJG52-1999 "spring tube type general pressure gauge, pressure vacuum gauge and vacuum gauge" verification procedures for the formulation of the permissible error of the pressure gauge. These 4 accuracy levels are: 1 level, 1.6 level, 2.5 level, 4 level. Allowable error (calculated as a percentage of the upper limit of measurement) are ±1%, ±1.6%, ±2.5%, ±4%. 3, China in 2005, the new digital pressure gauge calibration regulations published and implemented, in line with JJG875-2005 "digital pressure gauge calibration regulations. Provides for the pressure accuracy of ± 0.01%, ± 0.02%, ± 0.05%, ± 0.1%, ± 0.2%, ± 0.5%, ± 1.0%, ± 1.6%. 4, a reasonable choice of pressure gauge accuracy level method, should be based on the production process, economic practicality, testing methods and other requirements, according to the minimum value of the measured pressure required by the allowable error to select the accuracy level. Inspection and maintenance 1, after a period of use and pressure, the pressure gauge movement will inevitably appear some deformation and wear, the pressure gauge will produce a variety of errors and failures. In order to ensure its original accuracy and not make the value transfer distortion, should be replaced in a timely manner to ensure that the instructions are correct, safe and reliable. Pressure gauge (Figure 17) 2, the pressure gauge should be cleaned regularly. Because the internal pressure gauge is not clean, it will increase the wear and tear of the various components, thus affecting its normal work, serious pressure gauge failure, scrap. 3, in the pressure measurement parts of the installation of the pressure gauge, according to JJG52-1999 regulations, it is generally not more than half a year verification cycle. Relating to production safety and environmental monitoring of the pressure gauge, the verification cycle must be in accordance with the verification procedures, only less than half a year; if the mining conditions are harsh, the verification cycle must be shorter. 4, the pressure measurement part of the medium fluctuations, frequent use, high accuracy requirements, as well as more stringent safety requirements, according to the specific circumstances of the verification cycle will be appropriately shortened. The following four 11 types of pressure gauges need to be mandatory verification: 1, used for safety and security of the pressure gauge to be mandatory verification. Including the following 7 categories: 1) the measurement of the boiler main cylinder and feedwater pressure parts; 2) fixed air compressor air compartment and the measurement of the pressure of the main pipe; 3) generators, gas turbine oil pressure and locomotive pressure measurement; 4) medical autoclave sterilizer, autoclave pressure measurement; 5) with the measurement of the pressure of the alarm device; 6) sealing pressurized container pressure measurement; 7) hazardous, toxic, corrosive and serious media pressure measurement. (such as: spring tube pressure gauge, pressure gauge, pressure gauge, pressure gauge, pressure gauge, pressure gauge, pressure gauge, pressure gauge) (Such as: spring tube pressure gauge, electric remote transmission and electric contact pressure gauge). Pressure gauge (Figure 18) 2, used for safety protection of the wind pressure gauge need to be mandatory calibration. That is: the mine in the tunnel wind pressure, wind speed measurement. (Such as: mine wind pressure meter, mine anemometer). 3, for the safety and protection of oxygen meters need to be mandatory calibration. Including the following 2 categories: 1) in the process of filling oxygen cylinders oxygen monitoring pressure measurement; 2) in the process of explosive, affecting the safety of oxygen pressure measurement. 4, used for medical and health care oxygen meter is subject to mandatory calibration. That is, the hospital oxygen delivery with buoy oxygen inhaler and oxygen supply device on the oxygen pressure measurement. Frequently Asked Questions Pressure gauge is composed of several main parts, including connector, spring tube and movement. The welding of the pressure gauge is mainly lead-zinc welding, silver welding, argon arc welding, special welding, etc. The normal work of the instrument's clarinet is 100,000 times. Its working principle is through the spring tube deformation, movement (fan-type teeth and the center gear work) driven pointer in the face plate scale shows the measured medium pressure. Pressure gauge (Figure 19) Pressure gauge in the use of the process of three common problems: 1, the pressure gauge fan gear work for a period of time there will be wear and tear phenomenon; 2, the pressure gauge pressure measurement system is subject to the measured medium instantaneous overpressure impact, so that the pointer can not return to the zero position or rushed to the limit of the nail below; 3, the instrument pointer, in the The system does not return to zero position after the pressure is removed. Three ways to solve the common problems of pressure gauge: 1, increase the fan gear contact surface width, increase the contact surface (i.e., increase the modulus of the gear), in order to achieve anti-wear to increase the service life of the purpose; 2, in the instrumentation of the movement on the installation of the limit block, the measurement of the pressure system by the instantaneous impact of the movement of cylindrical gears and fan gears are not easy to unbuckle to solve the problem of pressure gauge By the impact pressure pointer does not return to zero or the pointer is washed to the limit of the problem behind the nail; 3, impact pressure measurement system to close the valve below the pressure gauge. Anti-corrosion measures Shell corrosion: 1, the use of corrosive gases and other recommended shell shell using stainless steel shell or shell spray PTFE, in order to extend the service life of the pressure gauge; 2, the use of high humidity environment is recommended to increase the level of protection shell, in order to prevent the external moisture into the table, to increase the service life of the pressure gauge. Liquid-connected part of the anti-corrosion: 1, for general corrosive media, if the stainless steel elastic components can withstand 1 to 2 years of corrosion, you can choose a general stainless steel pressure gauge, the installation, the guide pipe should be short, if necessary, buffer coils instead of buffer tanks, to prevent clogging of impurities. 2, if the medium of stainless steel and copper have a purpose corrosion, the buffer tank can be changed to isolation tank, add corrosion-resistant isolation fluid. The type of isolation fluid can be selected according to the nature of the measured medium, but requires the use of more than half a year without deterioration is good. If the ordinary isolation fluid can not be applied, the available chlorofluorocarbon oil as an isolation fluid, but the price is very expensive, so the isolation tank should be made small, when disassembled to recover the fluorine oil for reuse. 3, diaphragm pressure gauge can be used, there are molybdenum-containing stainless steel, Hastelloy and tantalum sheet, diaphragm and ballistic tube with methyl silicone oil between the pressure transfer, the minimum range can be done 0 ~ 100kPa, if the diaphragm material is not corrosion-resistant, then you can add a layer of F46 (polyperfluoroethylene propylene) diaphragm, but the instrument sensitivity has been reduced. F46 can also be used directly as an isolation diaphragm, but pay attention to the permeability of the medium, high temperature and oil media transfer fluid can be selected fluorine oil.