Piezoelectric crystal is a kind of electric energy and mechanical energy conversion of ceramic materials, which can convert mechanical energy into electrical energy, also can transform electrical energy into mechanical energy. Transistor by external pressure, in addition to generate mechanical deformation, charge generated in the crystal surface and the pressure ratio, the charge amplifier can charge into the corresponding voltage output, used in the manufacture of a piezoelectric force sensor, ultrasonic receiver.
The same electric field is applied on the piezoelectric crystal, dimension piezoelectric crystal will change a little, this phenomenon is called electrostriction phenomenon, because the mechanical deformation is produced by electric field, and the resistance of piezoelectric crystal is very large, almost no consumption of energy, can be made small, low-power components such as the buzzer, ultrasonic generator, a piezoelectric valve.
The pilot piezoelectric valve P9
HOERBIGER-ORIGA pilot piezoelectric valve P9 ( Figure 1 ) through the piezoelectric sheet work, the structure of thin elastic metal bonded piezoelectric film on both sides, in two working face of the piezoelectric sheet vacuum coating formed on two electrodes.
Fig. 1 Schematic diagram of the working principle of P9
No electricity when the compressed air input hole 1 is closed, the output hole 2 and hole 3 interlinked, the output pressure of 0; energized when the upper crystal shrinkage, lower crystal elongation, the leverage effect, make the mechanical deformation can be expanded to tens of microns, big hole 3 is closed, the compressed air from the hole to hole 1 2, produce output air pressure signal, piezoelectric bending degree varies with the variation of the input voltage, so the pilot piezoelectric valve P9 can be used as a switch or proportional valve. Voltage output pressure curve shown in Figure 2, the pilot piezoelectric valve response time is less than 2mS.
Figure 2 P9 pressure - voltage curve of HOERBIGER-ORIGA piezoelectric valve P20
( Figure 3 ) by pilot piezoelectric valve P9, switching power amplifier, miniature pressure reducing valve and 30 μ M filter consisting of 2 position 3 way valve.
Working voltage: 24VDC
Working current: <10μ A
Maintain current: 0μ A
Response time: <20mS ( reach
10% or 90% pressure )
Electric capacity: <100nF
Working pressure: 1.2-8.0Bar
Flow rate: 130 L/Min
( From 6 to 5 Bar )
Working temperature: -30 ~ +60
Fig. 3 Schematic diagram of the working principle of P20
Pressure gas path structure of intelligent valve positioner
Piezoelectric intelligent valve positioner gas path with two P20 piezoelectric valve ( PV1, PV2 ) and two one-way valve ( RV1, RV2 ) is composed of a control gas circuit, as shown in figure 4. Copyright dedecms
Intelligent valve positioner has a total of 3 kinds of pneumatic logic state.
When the actuator of a small amount of leakage or valve pipeline pressure caused by a sudden change in the valve position fluctuation, the smart positioner immediately by keeping state switching to the pulse state, because the response time of P20 to 20mS, the intake or exhaust pressure electric valve can be controlled to the minimum intake or exhaust quantity ( approximately 0 ), ensure the valve position disturbance control in the range of 1% error.
Fig. 4 Schematic diagram of gas path structure
Piezoelectric intelligent valve positioner control mode
Piezoelectric smart valve positioner with pulse width modulation mode PWM ( Pulse Width Modulation ) to drive the piezoelectric valve. When the control deviation is large, continuous output signal locator; when the deviation is small, the output pulse signal; when the deviation is very small, the pulse signal output smaller; when the deviation of the valve control accuracy range, no control command output, keep the position.
Piezoelectric intelligent valve positioner features
Because the core of pneumatic components are piezoelectric materials structure, which can be less movable parts, small volume, low power consumption, output of the gas flow can be continuously changed from 0 to 130L/Min, the piezoelectric smart valve positioner has many advantages.
High control precision, fast speed: the minimum flow of intake air or exhaust can be nearly 0, it is easy to control valve is adjusted to 1% or higher accuracy, in regulating valve 25 stroke 3Bar pressure switch, speed can be controlled within 2S.
Low consumption, shock resistance : valve positioner, pneumatic in maintaining state, compressed air consumption is almost negligible. Use of smart valve positioner is two normally closed piezoelectric valve, when the power of compressed air without emptying, reduces the use cost. No active nozzle flapper mechanism, the locator can eliminate the effect of external shock on the valve.
Low power consumption: drive current piezoelectric valve is 10 μA, without the need to maintain the current, is very important to take power from the 4-20mA signal or fieldbus instrument, can facilitate the use of LCD instructions, any branch, custom flow curve, valve output, limit switch, field bus function.
Maintenance is simple: modular structure, automatic tuning, characteristic parameters of the valve are saved to the locator, the user can know the use of the valve according to the original records, and provide a reliable basis for the maintenance of the valve.
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