On the smart valve positioner valve repair
Valve repair work, often encountered in supporting the valve positioner damaged, Jiangyin Oulei Si, working principle and structure is familiar with the valve positioner valve repair work, has played a very positive effect. Valve positioner pneumatic control valve accessory products, the long calendar production of valve positioner is to use the analog signal and the force balance principle method. In recent years, due to the development of electronic technology, the number of foreign launch smart valve positioner, because of its superior performance control high precision, good reliability, vibration resistance, convenient debugging, the flow characteristics can be modified online, can remote communication , by users of all ages. After years of research, the company developed the HVP intelligent valve positioner of the product by the CPU module, valve current feedback template, HART communication templates, alarm template, template, precision position sensors and I / P conversion units.
I / P conversion unit structure can be divided into: coil nozzle flapper valve and piezoelectric valve coil slip three structures. Since the coil nozzle flapper I / P conversion unit sweep simple structure, ease of manufacture, low cost and, therefore, I / P conversion unit the number of substantially all the cool traditional positioner With this structure. Coil spool type solenoid valve using piezoelectric valve-I / P converter unit, first appeared in the 1990s Siemens launched SIPARTPS intelligent valve positioners, because of its high resistance to vibration high reliability, low power consumption, and low air consumption and be able to accept a higher frequency of the control signal characteristics, ideal for smart valve positioner performance requirements of the I / P converter unit.
1 I / P conversion unit type
The main role of the I / P conversion unit is the electrical signal into a pneumatic signal, the nozzle back pressure and flow control through the amplification, so that it has sufficient power to operate the pneumatic control valve. Types of I / P conversion unit according to the air consumption is divided into: two structures of gas consumption style and not gas consumption. Because they do not consume the gas type I / P conversion unit consumption of gas when the small, easy and stable gas supply pressure, pressure magnification to improve the oscillation phenomena, gas consumption style I / P converter unit often used for valve positioner designs.
I / P conversion unit is an important one of the key components of the valve positioner, its controllability, anti-vibration, power consumption, gas consumption indicators will directly affect the performance of the whole design excellent I / P conversion unit one of the very important step in the intelligent valve positioner.
Works and technical indicators
(1) works
Piezoelectric valve is the actual use of the function the ceramic piece Um pressure role under the bending deformation theory made a two-(or proportional) control valve. Control the piezo valve operation simply provide sufficient voltage, the electric power consumption is almost zero. Its principle of operation: the piezoelectric valve in the initial state (not energized, as shown in Figure 1), the role of functional ceramic sheet in the nozzle opening 1, In this case, the opening 2 and the nozzle 3 is communicated with the pilot cavity is formed as a whole. When a piezoelectric valve when the power is turned on (as shown in Figure 2), the deformation of the functional ceramic sheet to the upturned mouth of the nozzle 3 Squeeze, so that the opening 2 and the nozzle opening communicating.
(2) Technical Specifications
1) Operating voltage: 240V DC
2) Rated working pressure: 120Kpa
3) Rated air flow: 1.5L/min
4) Leakage: 0.10 L / min
5) Capacitance: <100nF
6) energy consumption: 0W
7) Operating temperature: -30 to +80 ° C
8) exchange time: <2ms
9) medium: Air
10) Weight: 6g
3 structural principle
The piezoelectric valve in the I / P conversion unit from the role of the pilot, each I / P conversion means simultaneously apply two piezoelectric valves, piezoelectric valves I Control I / P conversion unit output signal (also called the feed valve), The piezoelectric valve II Control I / P conversion unit the exhaust gas (also known as an exhaust valve) as shown in its working principle FIG 3.
The piezoelectric valve due to the pilot pressure (i.e., the pilot chamber of the gas pressure) is too small, does not have the ability to generate an air stream, it must supercharging. The supercharger is in the completion of the servo section, and its role as if the pneumatic breaker. Servo section on one side of the pilot chamber has an area larger diaphragm, and a smaller area of the surface in the side of the output, and an exhaust chamber. This will force the one side surface of the mobile spool and the exhaust gas chamber when the pilot pressure reaches 120KPa, the force is applied in the pilot chamber side of the diaphragm, is greater than the force acting on the output and on the other side of the exhaust chamber, the pressure will be greater than the pilot pressure, so as to achieve the purpose of the pressurized.
When the power control circuit, no voltage on the piezoelectric valve I, the piezoelectric valve II plus voltage control, gas source KPa into the the piezoelectric valve II pilot chamber, the formation of a gas pressure of about 120KPa, the pilot pressure to promote exhaust spool is moved downward, the exhaust port is closed. Then if the control circuit to issue the output gas pressure pulses, the piezoelectric valve II to maintain the power-on state, the I plus control voltage of the piezoelectric valve, functional ceramic sheet bending the ceramic sheet blocking the nozzle opening of the piezoelectric valve 3, the gas source P2 through the nozzle opening into the the piezoelectric valve I pilot pressure chamber, forming a gas pressure of about 120KPa promote moves the plug is moved downward, the gas source P1 through the intake port into the membrane chamber of the pneumatic control valve, the driving pneumatic control valve position adjustment, the voltage becomes zero when it reaches the set position, the piezoelectric valve I, the pilot pressure chamber pressure becomes 0Kpa reset spring to push the mobile spool to close the output pneumatic regulating the gas pressure in the diaphragm chamber will remain at a relatively constant pressure. Control voltage is zero when To decrease the pneumatic regulating the gas pressure in the diaphragm chamber, the piezoelectric valve I the piezoelectric valve the II control voltage is also zero, the pressure guide chamber pressure also becomes 0Kpa, exhaust spool under the action of a spring in the exhaust gas, to open the exhaust vent, and to achieve the purpose of decompression of the membrane chamber. So constantly piezoelectric valve I II control, the I / P conversion unit continuously outputs the gas pressure and the exhaust gas, thereby driving the pneumatic control valve convection through the medium of the valve body flow regulator.
4 circuit control principle
The piezoelectric valve can adopt the on / off position control method, the control circuit is relatively simple, and the electronic switch can be realized. The basic schematic shown in Figure 4. Controlled switch K1, K2, K3 is a single pole double throw switch, K1 to control the intake valve, and K2 control the exhaust valve, K3 and K1, K2 complexes allows both ends of the piezoelectric homemaker generate reverse voltage, so that the non-energized state of the piezoelectric valve shut down and more reliable. Control of the state, there are three: a hold state, some time can be maintained for pneumatic actuators Lu current valve position; b intake status change when off valve position; c exhaust state, reset the valve position.
5 surge devices
Because standard electric valve rated pressure 120KPa, leaving the valve positioners normal work gas source pressure is generally between 140 ~ 500KPa into the piezoelectric valve operating pressure must therefore reaches its rated pressure by reducing the pressure to work properly . Currently, air filter Less wins the bulky main decompression structure, the weight is not light, this structure is used to adjust the working pressure of the piezoelectric valve is bound to make the I / P converter unit volume and weight, is not conducive to the actual Application. Piezoelectric valve I / P conversion unit, as shown in Figure 5 regulator structure, its main features: small size (only one-tenth of the conventional pressure reducer), wide adjustment range (0 to 800KPa) output stability.
Compressed air through a gap between the ball and the valve seat disc Ps through inlet flows into the diaphragm bottom with a given force of the spring piece phase equilibrium, so that the outlet pressure P is maintained at the desired value is stable. When adjusting screw clockwise rotation, the outlet pressure P increases. Conversely, the outlet pressure P decline. Work input pressure PS change the outlet pressure P is almost unaffected. This is because: when the PS increases, the role of increased pressure below the diaphragm, to promote the transition plate is moved upward, the return spring push the steel ball is moved upward, so that it is reduced to a gap between the seat disk, the pressure of the output port P will remain unchanged.
According to the relief valve theory, the regulation characteristics of the diaphragm to the effective pressure receiving area A1, and the effective area of the valve port A2 about:
△ P2 / △ P1 = 1 / (A1/A2-1)
P1: inlet pressure change △ P2 outlet pressure changes;
If the inlet pressure is between 140 ~ 800KPa change, pressure change amount: △ P1 = 800-140 = 660KPa, if the outlet pressure change value: △ P2 = 5KPa accordance with the above formula to calculate the ratio of the A1, A2.
A1/A2 = △ P1 / △ P2 +1 = 660/5 +1 = 133
If the diaphragm is an effective pressure receiving area A1 and the valve port of the comparison value of the effective area A2 is greater than 133, the inlet pressure to the outlet pressure can be varied between 140 ~ 800KPa changes less than 5KPa.
6 piezoelectric valve advantage of the I / P conversion unit
(1) greatly improves I / JP conversion unit vibration resistance
Always maintain traditional force-balance valve positioner in the work, between the baffle and the nozzle over a small distance, when the valve positioner installation environment of the vibration damper position easily swing around, leading to the instability of the valve positioner output . Figures 1 and 2 can be seen that the pairs of ceramic sheets in the piezoelectric valve in the pilot chamber, only two fixed positions, one is acting on the surface of the opening 1, the other is acting on the surface of the opening 3, which principle eliminated caused due to external vibration and dual ceramic wobble; Also, eliminating the need for the mechanical force balanced many parts, which may be the number of moving parts is greatly reduced, thereby improving the vibration resistance of the I / P conversion unit .
(2) low-power, low air consumption, the locator reduce operating costs
Intelligent locator uses a two-wire control room 4 ~ 20mA valve position signal sent to the valve positioner energy limited, both work to meet the circuit in various components work properly, but also can drive I / P converter unit, so the design of the various components of the electric power consumption must be strictly controlled. The piezoelectric valve is made of the functional ceramic sheet, a certain voltage is supplied, will be able to work, almost does not consume current. As the I / P conversion unit selection piezoelectric valve control components, reducing the power consumption of the machine.
When the regulating valve in a relatively stable regulation position, the intake port of the intake valve is closed, the exhaust valve of the exhaust port is also closed, so that the pneumatic regulation of the gas capacity of the diaphragm chamber is static over time, there is no air consumption. Traditional positioner in the pneumatic control valve when it reaches a certain stable value, the intake port has an air supply, exhaust air discharge port is always just equal to the gas volume and displacement only.
(3) compact structure
Uses piezoelectric control technology I / P conversion unit, the volume is significantly reduced, I / P conversion Dimensions only 30mmX45mmX63mm size.
(4) to make the machine more reliable
Functional ceramic pieces in use almost no wear, and the action is the life of noble style of billions, not in the product in use because the the piezoelectric valve damage, leading to product failure. Piezoelectric valves smart valve positioner is used, the minimum throttle aperture of 0.6mm or more, and the compressed air through the orifice before the first transition after micro transition from the decision on the structure of the whole product not clogged (the traditional the gas barrier throttle aperture only 0.3mm, the hole often impurities clogging).
In short, in the application of piezoelectric smart valve positioner control technology to overcome the traditional valve positioner can not overcome the problem, the valve positioner products to a new level, providing a pneumatic control valve system for complete control Choice of a new control.
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