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Pneumatic valve actuator control methods and working principle
Due to the current control methods and means more and more, in practical industrial control and industrial control, there are many ways to control the pneumatic actuator, the following are commonly used. (A) based on the development of SCM intelligent display control Intelligent display is used to monitor the working status of the valve, and control the valve during the implementation of the work of the instrument, which monitors the valve position by two position sensors to determine whether the valve is open valve or Off the valve state, through the programming record the number of valve switch, and there are two and the corresponding valve opening 4 ~ 20mA output and two feet normally open normally closed output contacts. Through these output signals, control the valve switch action. According to the system requirements, the intelligent valve display can be divided into three parts from the hardware design: analog part, digital part, key / display part. 1, the analog circuit mainly includes power supply, analog input circuit, analog output circuit of three parts. The power section supplies the entire circuit energy, including analog circuitry, digital circuitry and the energy supply for the display. In order to achieve the opening of the valve to read the remote control, the valve opening information needs to be sent to other control instruments, while the control instrument can be developed from a distance valve for a certain degree of opening, the system needs 1 4 ~ 20mA analog input signal and 1 ~ 2 4 ~ 20mA analog output signal. Analog input signal through the A / D converter into a digital signal corresponding to the opening of the valve to the digital part of the microcontroller, the filter can be output in the microcontroller. Valve opening information through the D / A converted into an analog signal output, used to connect the display shows the valve opening or connect to other control equipment. In this design system, all the digital data are used serial input and output, in order to save chip resources and space, the input 4 ~ 20mA analog conversion into digital, using the existing 4-way DA chip And the microcontroller system resources for 8-bit AD combination. 2, part of the digital circuit include: microcontroller, power-down protection, two monitoring pulse input signal, two normally open normally closed contact output conversion. In the design options currently widely used 51 series microcontroller AT89C4051. The AT89C4051 is a low-voltage, high-performance CMOS 8-bit microcontroller with 4K bytes of erasable, reprogrammable, read-only flash memory. It is fully compatible with the 80C51 and 80C52 in terms of performance, instruction set-up and pins by composing a multifunction 8-bit CPU flash memory in a single chip. Taking into account the power-down or restart the system, the need to maintain some of the previous valve settings in the instrument parameters, and data memory in the microcontroller does not have the power-down storage function, so the chip has extended a power-save function of the chip X5045. The X5045 is a programmable circuit that integrates the watchdog, power monitoring, and serial EEPROM functions. This combination of design reduces circuit board space requirements. The watchdog in the X5045 provides system protection, When the system sends a fault and exceeds the set time, the watchdog in the circuit will react to the CPU via the RESET signal. X5045 provides three time values ​​for the user to choose to use. Its voltage monitoring feature also protects the system from low voltage, and when the supply voltage drops below the allowable range, the system will reset until the supply voltage returns to a steady value. The X5045's memory and CPU interface via serial communication. A total of 4069 bits, you can press 512 × 8 bytes to place the data. X5045 pin arrangement, which has a total of eight pins, the function of each pin is as follows: CS: circuit selection, low active; SO: serial data output; SI: serial data input SCK: Line clock output; WP: write-protect input, active low; RESET: reset output; Vcc: power supply terminal; Vss: ground. INA is the input signal, which is the valve pulse signal (<10mA) collected by the photoelectric sensor. The signal is filtered by the bypass capacitor into the optocoupler, converted into the output of the OUT voltage signal into the microcontroller. The output voltage can be directly into the microcontroller I / O port. In the control, the request A, B two-way pulse is received when it is considered by the signal input, AB is forward, BA is reversed. Only one signal input does not count. Two normally open, normally closed changeover contact output. Used to connect the solenoid valve, by controlling the suction solenoid valve to control the pneumatic actuator for the corresponding valve or valve closing action. 3, the display part includes: SCM, 4 LED display, three status lights (automatic, forward, reverse), 3 buttons (MODE / SET button, up button, down button). Display part of the use of AT89C4051 microcontroller, used to control the 4-bit LED display, and the digital part of the microcontroller to communicate, but also on the controller mode to make the appropriate choice and control. There are 3 status indicators on the display, which are used to display the status of the actuator: forward, reverse, auto; 3 buttons: MODE / SET button, up button, down button to control the working mode of the actuator and some parameters Initialization. These three parts are connected through an interface to form a complete control system that controls actuators such as air motors. In the practical application of the basic requirements of a variety of performance indicators. (B) the use of PLC to control the system PLC in the control system is more and more widely used, as the program is made in OMRON's PLC above for development, so to OMRON PLC for introduction. Hardware: 1 computer, 1 set of PLC (including CPU, I / O module, ID212, OC224, AD003 module), 2 relays, 2 solenoid valves, 1 pneumatic valve actuator. The composition of the principle: the PC through the RS-232 serial port communication OMRON PLC, PLC programming and monitoring. PLC's I / O modules are connected to the input and output signals, respectively, where the input module is connected to the valve on the two position sensors, through the PLC input module ID211 indicator light on the order to display the valve switch state. The input module receives two-way valve detection pulse input, namely pulse A and pulse B. In the running state, the light A is on when the pulse A is input, and the light B is on when the pulse B is input. Enter the order of AB, said the open valve. The order of inputting is BA for closing the valve. Valve detection pulse A and B signal must be partially superimposed, otherwise it can not normally detect the valve opening. OC225 through the PLC output module control two relays, the relay has two normally open normally open output contacts, a group of open valve output contacts, a group of off valve output contacts. When the valve is opened, when the valve opening is greater than or equal to the set valve limit value, the valve opening output contact will act. When the valve opening degree is less than the set valve limit value, the valve opening output contact will act. The invention opening degree is smaller than the set valve Open limit valve output contact reset. When the valve is closed, when the valve is closed to zero and there is no pulse input within 21s, the closing valve output contact will act. If there is pulse input within 21s, the delay time 21s will close the valve output contact. Through the relay pull to control the two solenoid valve switch, the solenoid valve is open, you can control the pneumatic valve actuator so that the valve to do the appropriate opening or closing valve action. At the same time the proximity sensor to the valve switch and then sent to the PLC, and with the required valve opening for comparison until the meet the requirements. Automatic zero and auto-fill: the control system with automatic zero and auto-fill function, when the valve opening is less than zero range or the valve opening is less than the full scale range of full-scale adjustment range, and the time is greater than or equal to the set When the value is stable, the PLC automatically controls the valve to zero or automatically fill. In the experiment, the position of the valve on the valve to calculate the valve opening. When the valve leaves the A sensor first and then the B sensor, it means the valve is closing the valve. When the valve to leave the B sensor, leaving the A sensor, said the valve is open. The sensor receives a pulse signal, through the position sensor acquisition signal to note the valve switch state. In the host computer using the programming software CX-programmer to write ladder, and then download the ladder to run in the PLC, the host computer's configuration software for control and monitoring, how much the valve switch can be input by the configuration software interface circle Numerical determination. Configuration interface is done, the valve open, close the valve, stop, the main switch and other controls control and action can be directly in the configuration interface is very intuitive to operate. Pneumatic valve actuator working principle The use of compressed air to promote multiple combinations within the actuator pneumatic piston movement, transmission of force to the characteristics of the beam and the inner curve of the track, driven by the air core spindle for rotary motion, compressed air to lose the disk to the cylinder, change out Gas position to change the direction of rotation of the spindle, according to the load (valve) torque required for the rotation, the number of cylinder combinations can be adjusted to drive the load (valve) work. Two five-way solenoid valve is usually used with dual-acting pneumatic actuator supporting the use of two are two positions: on-off, five-way ventilation is five channels, of which one is connected with the gas source, two and double Cylinder of the role of the outer air chamber inlet and outlet connections, two with the internal air chamber inlet and outlet followed, the specific working principle can refer to double-acting pneumatic actuator working principle.