Jiangyin Thousands Chemicals Co. , https://www.jywqhxcomposite.com
Intelligent valve positioner in the piezoelectric valve I / P conversion unit
Valve positioner is a pneumatic valve to supporting products, the long history of the valve positioner is the use of analog signals and force balance principle and method to achieve. In recent years, due to the development of electronic technology, many foreign intelligent valve positioner, because of its high control accuracy, good reliability, good vibration resistance, easy commissioning, flow characteristics can be modified online, remote communications and other superior performance , By the user's favor. After years of research, our company has developed HVP intelligent valve positioner, which consists of CPU template, valve current feedback template, HART communication template, alarm template, display template, precision position sensor and I / P conversion unit. I / P conversion unit is one of the key components of valve positioner, its controllability, anti-vibration, power consumption, air consumption indicators will directly affect the performance of the whole machine, the design of excellent I / P conversion unit is One of the most important steps to realize intelligent valve positioner. 1 Type of I / P Conversion Unit The main function of the I / P conversion unit is to convert the electrical signal into a pneumatic signal that has sufficient power to operate the pneumatic control valve by amplifying the nozzle back pressure and flow control. I / P conversion unit types can be divided into air consumption: gas-consuming and non-gas-consuming two structures. Among them, the non-air-consuming I / P conversion unit is often used in the valve positioner because the gas consumption of the air-less I / P conversion unit is small, the pressure of the air source is easy to stabilize, the pressure magnification is small and the oscillation phenomenon is improved. designing. I / P conversion unit according to the structure of the form can be divided into: coil nozzle baffle, coil valve and piezoelectric valve three structures. As the coil nozzle baffle I / P conversion unit scanning structure is simple, easy to manufacture, low cost, therefore, the traditional valve positioner I / P conversion unit greatly Shuangshu this structure. Solenoid valve spool valve is mainly used in the solenoid valve, piezoelectric valve I / P conversion unit, the earliest appeared in the 20th century, 90 Siemens launched SIPARTPS intelligent valve positioner, because of its high anti-vibration, High reliability, low power consumption, low air consumption, and control signals capable of accepting higher frequencies are ideal for intelligent valve positioners for the performance requirements of I / P conversion units. 2 Piezoelectric valve working principle and technical indicators (1) Working principle Piezoelectric valve is actually a function of the use of functional ceramics under pressure caused by bending deformation of a two-way (or proportional) control valve. Control the piezoelectric valve action only need to provide enough voltage, power consumption is almost zero. The action principle: the initial state of the piezoelectric valve (no electricity, as shown in Figure 1), the role of ceramic in the nozzle port 1, this time, the mouth 2 and the nozzle 3 and the pilot cavity connected to form a whole. When the piezoelectric valve is powered on (as shown in FIG. 2), the functional ceramic sheet is deformed to be upturned, and the nozzle opening 3 is pressed so that the opening 2 communicates with the nozzle opening 1. (2) Specifications 1) Operating voltage: 240V DC 2) Rated working pressure: 120Kpa 3) Rated air flow: 1.5L / min 4) Leakage: 0.10L / min 5) Capacitance: <100nF 6) Energy consumption: 0W 7 ) Working temperature: -30 ~ + 80 ℃ 8) Exchange time: <2ms 9) Media: Air 10) Weight: 6g 3 Structure Principle Piezo valve plays a leading role in I / P conversion unit. Each I / P The conversion unit also applies two piezoelectric valves, the piezoelectric valve I controls the output of the I / P conversion unit (also called intake valve), the piezoelectric valve II controls the exhaust of the I / P conversion unit (also called the exhaust valve) The working principle shown in Figure 3. The piezoelectric valve must be supercharged because the pilot pressure (ie, the pressure in the pilot chamber) is too small to have the ability to generate air flow. Booster is completed in the servo part, its role is like a pneumatic breaker. The servo section has a large area diaphragm on the pilot chamber side and a smaller area on the output and exhaust chamber sides. When the pressure reaches 120 kPa, the force exerted on the diaphragm on one side of the pilot chamber is greater than the force on the other side of the output and exhaust chambers, which forces the moving spool and the side of the exhaust chamber The pressure will be greater than the pressure, so as to achieve the purpose of pressurization. When the control circuit is connected to the power supply, there is no voltage on the piezoelectric valve I. The voltage of the piezoelectric valve II is controlled by the voltage. The gas source KPa enters the pilot chamber of the piezoelectric valve II to form a gas pressure of about 120KPa. The pilot pressure drives the exhaust gas Spool to move down, the exhaust port closed. At this time, if the control circuit sends a pulse of output gas pressure, the piezoelectric valve II will maintain the power-on state, the piezoelectric valve I will control the voltage, the functional ceramic will be bent, the ceramic will block the piezoelectric valve nozzle 3, The nozzle port 1 enters the pressure guiding chamber of the piezoelectric valve I. The gas pressure around 120KPa is formed to push the moving valve core to move downwards. The gas source P1 enters the membrane chamber of the pneumatic control valve through the air inlet port to drive the pneumatic control valve Position adjustment, when it reaches the set position, the piezoelectric valve â… voltage becomes zero, the pressure in the pressure chamber becomes 0KPa, the return spring to promote the movement of the spool to close the output port, the pneumatic pressure in the diaphragm valve chamber Will be maintained at a relatively constant pressure. When it is necessary to reduce the gas pressure in the pneumatic regulating valve membrane chamber, the control voltage of the piezoelectric valve I is zero, the control voltage of the piezoelectric valve II is also zero, and the pressure of the pilot pressure chamber also becomes 0KPa. The exhaust valve core Under the action of the exhaust spring, the exhaust port is opened to exhaust to achieve the purpose of decompression of the membrane chamber. This constantly on the piezoelectric valve â… , â…¡ control, I / P conversion unit continuously output gas pressure and exhaust, which drives the pneumatic valve to flow through the valve body flow control. 4 circuit control principle Piezoelectric valve can adopt on / off position control method, the control circuit is simple, the use of electronic switches can be realized. The basic principle is shown in Figure 4. Control switch K1, K2, K3 single-pole double-throw switch, K1 control intake valve, K2 control exhaust valve, K3 and K1, K2 can make the piezoelectric strain of both ends produce reverse voltage so that the piezoelectric valve is not energized state Shut down more reliable. There are three control states: a Hold state, the current valve position of the pneumatic actuator can be maintained for a while; b Intake state, change the valve position; c Exhaust state, the valve position is reset. 5 pressure regulator device due to the standard valve rated pressure of 120KPa, leaving the valve positioner normal working gas pressure is generally between 140 ~ 500KPa, therefore, into the piezoelectric valve operating pressure must be reduced to reach its rated pressure In order to work properly. At present, the main structure of the air filter snubber decompression structure bulky, the weight is not light, if this structure is used to adjust the working pressure of the piezoelectric valve is bound to I / P conversion unit volume and weight are increased, is not conducive to the actual application. In the piezoelectric valve I / P conversion unit used in Figure 5 shows the pressure regulator structure, its main features: small size (only one-tenth of the conventional pressure reducer), wide adjustment range (0 ~ 800KPa) , Output stability and so on. The compressed air Ps flows through the gap between the ball and the valve seat disk through the inlet to balance with the force of a given leaf spring so that the outlet pressure P remains constant at the desired value. When turning the adjusting screw clockwise, the outlet pressure P increases. On the contrary, the outlet pressure P decreased. In the work input pressure PS changes, the outlet pressure P is almost unaffected.This is because: when Ps increases, the role of pressure in the diaphragm under the pressure to promote the transition plate upward movement, the return spring to push the steel ball up to its The gap between the valve plate and the disk is reduced and the pressure P at the output port will remain unchanged. According to the theory of the pressure reducing valve, the adjusting characteristic is related to the effective pressure area A1 of the diaphragm and the effective area A2 of the valve opening: â–³ P2 / â–³ P1 = 1 / (A1 / A2-1) P1: Change of inlet pressure, If the inlet pressure changes between 140 ~ 800KPa, the pressure change: â–³ P1 = 800-140 = 660KPa, if the outlet pressure change value is: â–³ P2 = 5KPa then according to the above formula can calculate the A1, A2 ratio . A1 / A2 = ΔP1 / ΔP2 + 1 = 660/5 + 1 = 133 If the effective pressure area A1 of the diaphragm and the effective area A2 of the valve port are greater than 133 and the inlet pressure changes between 140 and 800KPa, Export pressure changes less than 5KPa. 6 Piezoelectric valve I / P conversion unit advantages (1) greatly improved anti-vibration I / JP conversion unit Traditional balance valve positioner in the work, the baffle and the nozzle always maintain a slight distance between, When the valve positioner installed in a larger vibration environment, the baffle position is easy to swing around, resulting in unstable output valve positioner. As can be seen from Figures 1 and 2, the dual ceramic plate has only two fixed positions in the pilot valve cavity of the piezoelectric valve, one acting on the surface of port 1 and the other acting on the surface of port 3, In principle, it eliminates the double ceramic oscillation caused by external vibration. In addition, many parts with balanced mechanical force are eliminated, the number of movable parts is greatly reduced, thereby improving the anti-vibration performance of the I / P conversion unit . (2) low power consumption, low air consumption, the locator to reduce operating costs Intelligent locator using two-wire work, the control room to the valve positioner 4 ~ 20mA valve position signal energy is limited, it both work to meet the circuit A variety of components to work properly, but also be able to drive I / P conversion unit, so the design of the various components of the power consumption must be strictly controlled. Piezoelectric valve is made of functional ceramic, can supply a certain voltage can work, almost no current consumption. Selection of piezoelectric valve as I / P conversion unit control components, reducing the power consumption of the machine. When the control valve is in a relatively stable control position, the inlet of the intake valve is closed and the exhaust of the exhaust valve is closed, so that the gas capacity of the pneumatic valve chamber is static for a period of time, Air consumption. The traditional valve positioner in the pneumatic control valve reaches a certain stability value, the air inlet always has air supply, exhaust air outlet always has, but the amount of air supply and exhaust equal. (3) compact structure Using piezoelectric control technology I / P conversion unit, greatly reduced size, I / P conversion form factor is only 30mmX45mmX63mm size. (4) To make the whole machine more reliable. Because the functional ceramic pieces hardly wear during use and the operation life is noble and the style reaches billions, the products will not be damaged due to the damage of the piezoelectric valve. In the use of the piezoelectric valve smart valve positioner, the minimum throttle aperture are more than 0.6mm, and compressed air through the throttle before the first transition through the micro-transition, the structural decision on the whole product Will not be blocked (the traditional product of the air resistance throttling aperture of only 0.3mm, the hole is often clogged with impurities). In short, the application of piezoelectric valve positioner in the piezoelectric control technology to overcome the traditional valve positioner can not overcome the problem, but also to the valve positioner product to a new level, for complete sets of control system in the pneumatic control valve provides a New control options. More Keywords Search: Valve