Two-position five-way solenoid valves are usually used with double-acting pneumatic actuators. Two positions are controllable: on-off, five-way is five-channel ventilation, one of which is connected to the air supply, two and two The inlet and outlet ports of the external air chamber of the cylinder are connected, and the two inlet and outlet ports of the internal air chamber are connected. The specific working principle can refer to the working principle of the double-acting pneumatic actuator. (Editor: Global Hardware Network) UL Horizontal Vertical Flame Chamber Ul Horizontal Vertical Flame Chamber,Horizontal Vertical Flame Chamber,Vertical Horizontal Flame Test Machine,Vertical Horizontal Combustion Chamber Dongguan Best Instrument Technology Co., Ltd , https://www.dgbestinstrument.com
Several control methods for pneumatic actuators I. INTRODUCTION Air motors, as an actuator, play an important role in industrial production and industrial control. The air motor uses air instead of electric power and hydraulic pressure to generate power. It can realize stepless speed change, instant start, stagnation and reversing. It has automatic cooling function, no electric spark, and can be flammable and explosive, such as containing chemicals and flammability. Or volatile substances and other substances operating in humid heat and dusty environments, such as mining areas, tunnels, paint factories, chemical factories, petrochemicals, biotechnology, pharmaceutical companies, wafers, semiconductors, optical fibers, arsenals, ships, aquaculture, etc. Because air is used as power, it is easy to obtain. After use, the air can be directly discharged into the atmosphere without pollution. The compressed air can also be concentrated and remotely controlled.
Second, the working principle of pneumatic valve actuator uses compressed air to push the movement of multiple sets of combined pneumatic pistons in the actuator, transmits the force to the characteristics of the beam and the inner curved track, drives the hollow core spindle to rotate, and compresses the air disk to each cylinder. Change the inlet and outlet position to change the direction of the spindle rotation. According to the required rotation torque of the load (valve), the number of cylinder combinations can be adjusted to drive the load (valve).
Third, the control method of pneumatic valve actuators Because of the current control methods and means more and more, in the actual industrial life and industrial control, there are many methods used to control pneumatic actuators, commonly used the following.
(1) Intelligent display instrument based on single-chip microcomputer control The intelligent display instrument is an instrument used to monitor the working state of the valve and control the valve's execution period. It monitors the working state of the valve through two position sensors to determine whether the valve is open or not. The valve is closed, the number of the valve switch is programmed, and there are two 4-20 mA outputs corresponding to the valve opening and two normally open normally closed output contacts. Through these output signals, the switching action of the valve is controlled. According to the requirements of the system, the intelligent valve display can be divided into three parts from the hardware: analog part, digital part, button/display part.
1. The analog circuit part mainly includes three parts: power supply, analog input circuit and analog output circuit.
The power section supplies the entire circuit energy, including analog circuitry, digital circuitry, and the displayed energy supply. In order to realize the remote control of the valve reading, it is necessary to transmit the opening information of the valve to other control instruments. At the same time, the control instrument can make the valve from a distance to a certain degree of opening. The system needs one channel of 4-20 mA analog input signal and 1 to 2 channels of 4 to 20 mA analog output signals. The analog input signal is converted into a digital signal corresponding to the valve opening degree by A/D conversion, and then sent to the digital part of the single-chip microcomputer, which can be output after being filtered by the single-chip microcomputer. The opening information of the valve is converted into an analog signal output after D/A conversion, and is used to connect the display device to display the valve opening degree or to connect other control devices. In this design system, all digital data adopts serial input and output mode. In order to save chip resources and space, the input 4~20mA analog quantity is converted into digital quantity, and the existing 4-channel DA chip is used. Cooperate with the system resources of the single-chip microcomputer and use 8-bit AD.
2. The digital circuit part mainly includes: single-chip microcomputer, power-down protection, two-way monitoring pulse input signal, and two-way normally open normally-closed switching contact output.
In the design scheme, the currently used 51 series single chip microcomputer AT89C4051 is selected. The AT89C4051 is a low voltage, high performance CMOS 8-bit microcontroller with 4K bytes of erasable, reprogrammable, read-only flash memory. By combining a versatile 8-bit CPU flash in a single chip, it is fully compatible with the 80C51 and 80C52 in performance, command settings and pins.
Considering that some system parameters previously set in the meter need to be maintained when the system is powered down or restarted, and the data memory in the microcontroller does not have the power-down storage function, a chip with power-down saving function is extended off-chip. X5045. The X5045 is a programmable circuit that combines the functions of watchdog, power supply monitoring and serial EEPROM. This combination design reduces the need for board space. The watchdog in the X5045 provides protection for the system. When the system sends a fault and exceeds the set time, the watchdog in the circuit will respond to the CPU via the RESET signal. The X5045 provides three time values ​​for the user to choose from. Its voltage monitoring function also protects the system from low voltages. When the supply voltage drops below the allowable range, the system resets until the supply voltage returns to a stable value. The X5045's memory and CPU can be interfaced via serial communication. A total of 4069 bits can be placed in 512 x 8 bytes.
The pin arrangement of the X5045 is shown in Figure 1. It has 8 pins. The functions of each pin are as follows:
CS: circuit selection terminal, active low;
SO: serial data output;
SI: serial data input terminal;
SCK: serial clock output;
WP: write protection input, active low;
RESET: reset output;
Vcc: power supply terminal;
Vss: Ground.
The INA is the input signal and is the valve pulse signal (<10mA) collected by the photoelectric sensor. The signal is filtered by the bypass capacitor and sent to the optocoupler, which is converted into an output OUT voltage signal and sent to the microcontroller. The output voltage can be directly entered into the I/O port of the microcontroller. In the control, when both A and B pulses are required to be received, it is considered to be input by the signal, AB is forward rotation, and BA is reverse rotation. Only one signal is input when it is not counted.
Two normally open, normally closed switching contact outputs. Used to connect the solenoid valve, control the pneumatic actuator to control the valve opening or closing by controlling the suction of the solenoid valve.
3. The display part mainly includes: single-chip microcomputer, 4-digit LED display, 3 status indicators (automatic, forward, reverse), 3 buttons (MODE/SET button, up button, down button).
The display part adopts AT89C4051 single-chip microcomputer, which is used to control the 4-digit LED display, and communicate with the single-chip microcomputer of the digital part, and also make corresponding selection and control of the mode of the control instrument. There are 3 status indicators on the display to display the status of the actuator: forward, reverse, automatic; 3 buttons: MODE/SET button, up button, down button, control the operating mode of the actuator and some parameters Initialization. These three parts are connected by interfaces to form a complete control system that can control some actuators like pneumatic motors. In the actual application, various performance indicators required in advance are basically realized.
(II) System controlled by PLC The application of PLC in the control system is more and more extensive. Since this solution is developed on the PLC of OMRON, it is introduced by OMRON PLC.
Hardware components: 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 principle is as follows: the PC is connected to the OMRON PLC through RS-232 serial communication, and the PLC is programmed and monitored. The I/O modules of the PLC are respectively connected to the input and output signals, wherein the input module is connected to the two position sensors on the valve, and the switch state of the valve is displayed through the sequence of the indicator lights of the input module ID211 of the PLC. The input module receives two valve detection pulse inputs, namely pulse A and pulse B. In the running state, the indicator A is on when the pulse A is input, and the indicator B is on when the pulse B is input. The input order is AB, indicating that the valve is open. The input order is BA to indicate that the valve is closed. The valve detection pulse A and B signals must be partially superimposed, otherwise the valve opening cannot be detected normally.
Two relays are controlled by the output module OC225 of the PLC. The relay has two sets of normally open normally closed output contacts, one set is an open valve output contact, and one set is a closed valve output contact. When the valve is opened, when the valve opening degree is greater than or equal to the set limit value of the valve, the valve output contact action is actuated. When the valve opening degree is less than the set limit value of the valve, the valve output contact action is actuated, and the invention opening is smaller than the set valve. The valve output contact is reset when the limit value is reached. When the valve is closed, when the valve is closed to zero and there is no pulse input within 21s, the valve output contact will be closed; if there is a pulse input within 21s, the delay 21s will close the valve output contact. The two solenoid valves are controlled by the pull-in of the relay. After the solenoid valve is opened, the pneumatic valve actuator can be controlled to make the valve open or close. At the same time, the proximity sensor transmits the switch condition of the valve to the PLC and compares it with the required valve opening until it meets the requirements.
Automatic zeroing and automatic adjustment: The control system has automatic zero return and automatic full adjustment function. When the valve opening degree is less than the zero return range value or the valve opening degree is less than the full scale adjustment range value, 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 adjust.
In the experiment, the opening of the valve was calculated from the position sensor on the valve.
When the valve leaves the A sensor first and then leaves the B sensor, it indicates that the valve is closing the valve. When the valve leaves the B sensor first and then leaves the A sensor, it indicates that the valve is open. The sensor receives a pulse signal, which is recorded by the position sensor to record the switch state of the valve.
In the host computer, use the programming software CX-programmer to write the ladder diagram, then download the ladder diagram to the PLC to run and control and monitor it in the configuration software of the host computer. The number of valve switches can be input by the configuration software interface. The value is determined. After the configuration interface is completed, the control and action of the control such as opening the valve, closing the valve, stopping, and the main switch can be operated intuitively and directly in the configuration interface.
IV. Conclusion The two air motor control methods introduced above have been used in the production control process of some petrochemical plants, and have realized the expected functional control. The system developed by the single-chip microcomputer has a simple structure and convenient control. The control system developed by PLC has a relatively large initial investment, but it is better than the development system of the single chip in terms of stability and control accuracy.