Electric valve and pneumatic valve advantages and disadvantages pneumatic valve actuator control method

Electric valve and pneumatic valve advantages and disadvantages pneumatic valve actuator control method

The operating temperature determines the application environment temperature of the valve, and the nominal diameter of the valve is determined by the operating temperature. By the calculated uniform value of the valve to determine the torsion spring or rod uniform category, and then according to the application of material to determine the valve material structure form, and then according to the valve leakage volume rise calculate the valve throat diameter.
The following are the general rules for valve selection.
Valve electric actuators are widely used in power plants or nuclear battery plants, after all, in the high-pressure water gun system software needs a smooth, stable and slow process. The important advantage of the electric actuator is the high stability and the relatively stable thrust that the user can use. The thrust generated by the very large actuator can be as high as 225000kgf. Only the hydraulic actuator can achieve such a large thrust, but the engineering cost of the hydraulic actuator will be much higher than the electric one. The anti-offset level of the electric actuator is very good. The output thrust or torque is basically relatively stable, which can get rid of the unbalanced force of the medium and achieve the accurate control of the process index. Therefore, the control precision is higher than that of the electric actuator. If the servo amplifier is applied, it can easily complete the exchange of positive and negative effects, and also easily set the position of the break signal valve (maintain/open/close), and the fault must be limited to the origin, which is also not done by the electric actuator, the electric actuator must rely on a set of protective system to achieve the position protection. The defects of electric actuator mainly include complex structure, more likely to occur common faults, and because of its diversity, the technical requirements for construction maintenance personnel will be relatively high; The motor operation should be hot, if adjusted too frequently, easy to cause motor overheating, resulting in overheating protection, but also strengthen the wear of the reduction gear; There is also the relatively slow operation, from the controller output a signal, to adjust the valve response and fitness exercise to the corresponding part, it must be a long time, this is also compared with the pneumatic, hydraulic actuator area. Valve electric actuator management mechanism and driving mechanism is a unified whole, its management mechanism has plastic film type or piston machine two categories.
Piston machine stroke arrangement is long, applicable to the existence of a certain thrust place; The membrane stroke arrangement is smaller, and only the seat is pushed immediately. Because the pneumatic actuator has the characteristics of compact structure, large output thrust, stable and reliable posture, and safety and explosion-proof, some applications in the production of power stations, chemical plants, oil refineries and other high safety requirements. The main characteristics of the pneumatic actuator: accept continuous gas data signal, output parallel line offset (power/gas conversion equipment, can also accept continuous electronic signals), some plus the arm, can output angular velocity.
There are positive and reaction forces.
The movement speed is high, but the speed slows down as the load increases.
The output force is related to the operating temperature.
High reliability, but the valve can not be maintained after the final break of the pneumatic valve (can be maintained after adding the retaining valve).
It is not convenient to complete the section control and flow control.
Easy maintenance, good adaptability to the environment.
Output The output power is large.
With fire protection function.
The control method of pneumatic valve actuator is because there are more and more control methods and modes nowadays. In the specific industrial production and industrial production control, the methods used to control pneumatic actuators are also very many. The common ones are as follows.
Intelligent display instrument is used to detect the operating state of the valve, and control the valve guarantee period of the relevant work of the instrument and equipment, mainly through the dual phase sensor to monitor the valve working environment, distinguish the valve in the open valve or closed valve, according to the program written record valve switch data, And there are two ways corresponding to the valve opening 4 ~ 20mA output and bipedal normally open normally closed output contact.
Through this output data signal, control valve power switch position.
According to the requirements of system software, the intelligent valve display instrument can be divided into three parts from the hardware design and production: simulation part, data part, function key/indication part.
1, digital integrated circuit part mainly includes switching power supply, analog input power supply circuit, analog input and output power supply circuit three parts.
The switching power supply section provides all power circuit kinetic energy, including digital integrated circuits, digital circuit design and labeled energy requirements.
To realize the remote control of valve opening, the valve opening information content needs to be transmitted to other control dashboard, at the same time control dashboard can be developed from a distance valve for a certain opening, the system software must be a 4 ~ 20mA analog input data signal and 1 ~ 2 4 ~ 20mA analog input and output data signal.
The analog input data signal is transformed into the analog signal corresponding to the valve opening according to A/D and then presented to the data part of the single-chip microcomputer design, and it can be output after filtering processing on the single-chip microcomputer design. The opening information content of the valve is transformed into A digital signal output according to D/A, which is used to connect the display instrument to indicate the opening of the valve or connect other control machines and equipment. In the design tool, each digital signal data information adopts the serial communication of the input output method, in order to save the processing chip network resources and space, input 4 ~ 20mA analog input when the input into the volume, the existing 4-channel DA processing chip and 51 microcontroller server resources closely combined for 8-bit AD application.
2. Part of digital circuit design mainly includes: single-chip microcomputer design, power failure protection, double-channel detection of single pulse input signal, double-channel normally open normally closed conversion contact output.
In the design of the program, AT89C4051 is widely used at this stage.
AT89C4051 is a low-voltage, high-performance CMOS8-bit microcontroller with 4K byte erasable, repeatable program writer-protected flash memory chip.
In order to compound a multifunctional 8-bit CPU flash chip in the soc chip, in the characteristics, command Settings and pins and 80C51 and 80C52 completely adapt.
It is fully considered that when the equipment is powered off or restarted, it is necessary to maintain some main parameters of valves previously set in the instrument panel, and the memory in the single-chip microcomputer design does not have the function of power off storage, so a chip X5045 with power off storage function is expanded outside the chip.
X5045 is a programmable power circuit that integrates watchdog 1, power monitoring and serial communication EEPROM. This kind of combined design can reduce the need of power circuit for circuit board indoor space. Watchdog 1 in X5045 provides maintenance for the system. The watchdog 1 on the circuit board will take a RESET data signal to the CPU.
The X5045 brings three time values for the user to choose an application.
It has the function of working voltage monitoring can also protect the system from the influence of low voltage, when the power current falls below the allowable range, it will be automatically calibrated until the power current returns to the stable value.
The X5045 memory chip can communicate with the CPU through the serial port.
A total of 4069 characters can be displayed in 512 x 8 bytes.
The pin layout of X5045 is shown in Figure 1 below. It has 8 pins in total, and the efficacy of each pin is shown as follows: CS: select end of power circuit, reasonable low electrical frequency; SO: serial data output terminal; SI: serial data input terminal; SCK: serial communication digital clock output terminal; WP: write protection input, low power frequency is reasonable; RESET: calibrate output terminal; Vcc: switching power supply terminal; Vss: ground terminal.
INA is the input signal, which is the differential signal of the valve (10mA) collected by the infrared sensor. The data signal is filtered by the filter capacitor and then sent to the optocoupler, which is converted into the output voltage signal and sent to the MCU design.
The output voltage can be directly into the I/O port designed by the single chip microcomputer. In control, only when both A and B dual-channel single pulses are received can it be considered that the input is through data signal, AB is positive turn and BA is reverse.
Do not count when only one data signal is typed.
Double open and close, normally open and normally closed change contact output.
Used to connect relays, according to the control solenoid valve suction to control the pneumatic actuator for the corresponding valve opening or closing position.
3. Part of the demonstration mainly includes: single-chip microcomputer design, 4-bit LED demonstration, 3 status lights (automatic, forward, reverse), 3 function keys (MODE/SET key, up key, down key).
The AT89C4051 single chip microcomputer is used to control the 4-bit LED display, and the communication with the data part of the single chip microcomputer design, but also to do the corresponding choice and control of the controller.
The display instrument is provided with three status lights to indicate the status of the actuator: clockwise rotation, reversal, automatic; Three function keys: MODE/SET key, up key, down key, control the working mode of the actuator and some parameters reset.
These 3 parts are connected according to the jack, forming a complete control system software, which can control some similar pneumatic pumps and other actuators. In practical application, all kinds of performance parameters of pre-standard are basically completed.
(two) the use of PLC to control software in the control system software more and more, because this plan to do the development and design of OMRON’s PLC above, so to OMRON’s PLC to make an introduction.
Hardware configuration: 1 computer, 1 set of PLC (including CPU, I/O control module, > Its composition principle is: by PC according to RS-232 serial communication connected to OMRON PLC, to carry out programming and supervision of PLC.
PLC I/O control module respectively connected to the input, output data signal, in which the input module is transmitted to the valve in the 2 phase sensor, according to the PLC input module > according to the PLC output control module OC225 control 2 solenoid valve, solenoid valve with 2 groups of normally open normally closed output contact, 1 group for the open valve output contact, 1 group for the closed valve output contact.
When opening the valve, when the valve opening is greater than or equal to the special valve positioning value after opening the valve output contact position, the valve opening is lower than the special valve positioning value after opening the valve output contact position, create the invention of opening the valve output contact calibration after the opening is lower than the special valve positioning value.
When closing the valve, when the valve is closed at zero position and there is no single pulse input within 21s, the valve output contact position is closed; If there is a monopulse input in 21s, delay 21s off valve output contact position.
According to the suction of the solenoid valve to control the power switch of the two solenoid valves, the relay is opened, and the pneumatic valve actuator can be controlled to promote the valve to do the corresponding opening or closing position.
At the same time, the proximity switch to the valve power switch situation is transferred to the PLC, and compared with the standard valve opening until it meets the requirements of the cut-off.
Full automatic zero and full automatic setting: the control system software has the function of automatic zero and full automatic setting. When the valve opening is lower than the return to zero range value or the valve opening distance full is lower than the full adjustment range value, and the time is greater than or equal to the set value of the stable time value, PLC automatic control valve to carry out the return to zero or full automatic setting.
In experimental operation, the valve opening is measured by a phase sensor in the valve.
When the valve leaves sensor A first and then sensor B, it indicates that the valve is closing.
When the valve leaves sensor B first and then sensor A, it indicates that the valve is open.
The sensor receives a differential signal, which records the valve status according to the data signal collected by the phase sensor. The subprogram is written by CX-programmer, a numerical control programming software, and downloaded to PLC for operation. The subprogram is controlled and supervised in the configuration of the upper computer software. The amount of the valve power switch can be defined by the input circle value on the configuration page.
After the configuration software page is completed, the control body actions of valve opening, valve closing, terminating and main gate control can be operated directly in the configuration software interface very vividly. Pneumatic valve actuator principle uses compressed gas to promote the reciprocating pneumatic motion of multiple components in the actuator, supports the characteristics of the bearing beam and the internal curve rail, promotes the rotary movement of the hollow spindle bearing, transmits the compressed gas disc to each cylinder, changes the air inlet and outlet parts to change the direction of the spindle bearing, and changes the direction of the spindle bearing according to the requirements of the rotation torque of the load (valve). Can adjust the number of cylinder composition, push the load (valve) in operation.
Two-position five-way relay is usually used in combination with dual-effect pneumatic actuator, and two-position is controllable in two parts: Open-off, five-way has five safety channels for air exchange, of which 1 is connected with the pneumatic valve, 2 are connected with the inlet and outlet of the internal brake chamber of the double acting cylinder, and 2 are continuous with the inlet and outlet of the internal structure brake chamber. The actual working principle can be referred to the principle of double effect pneumatic actuator.