Abstract: In order to meet the requirements of control precision and stability of industrial valves in the field of industrial control, an intelligent valve positioner based on MSP430 single-chip microcomputer is designed. The positioner uses the MSP430F5438 as the core controller, the execution unit selects the high-speed on-off solenoid valve, and the control algorithm adopts fuzzy control tuning PID parameters. In addition to precise positioning, the positioner also has many additional functions such as self-tuning, self-diagnosis, and valve position output. After a brief description of the design principle and control requirements of the system, the hardware circuit and software were designed according to the modular design method. Experimental results show that the system has the characteristics of high control accuracy, good stability, rich functions, high degree of intelligence, and easy maintenance.
Key words: smart valve positioner; hardware design; software design; solenoid valve; fuzzy control ?05
Abstract: In allusion to the control precision and stability requirements of the regulating valve in the industrial control field, an intelligent valve positioner based on MSP430 SCM is designed. In the positioner, MSP430F5438 is used as the core controller, the high?speed switching solenoid The valve is selected for the execution unit, and the fuzzy control is used in the control algorithm to tune the PID parameters. In addition to the function of accurate positioning, the positioner also has various auxiliary functions such as self?tuning, self?diagnosis and The experimental results show that the system has the characteristics such as high control precision and stability. , rich functions, high intellectualized degree, and easy maintenance.
Keywords: intelligent valve positioner; MSP430F5438; hardware design; software design; solenoid valve; fuzzy control
Valve positioner is an important instrument in the field of industrial process control. It has been widely used in petrochemical, water conservancy, metallurgy and other industries [1]. Due to the gap in related technology, the domestic market has been dominated by large foreign companies. In order to revitalize the national industry, this article has developed a high-performance intelligent valve positioner based on MSP430 microcontroller, which has complete functions and good positioning effect.
1 System Design Principle Figure 1 shows the basic structure of a smart valve positioning system. The system will convert the 4-20 mA (or other signal system) setting signal into a digital signal and send it to the microprocessor. At the same time, the valve opening information will be converted back to the microprocessor through the displacement sensor. The microprocessor will make the difference between the two signals. If the deviation is in the dead zone range, the two switch solenoid valves will be in the cut-off state; otherwise, the corresponding PWM control signal will be controlled by the valve position control algorithm according to the size of the deviation. The two solenoid valves are turned off. In this way, the actuator's compressed air flow is adjusted, which in turn pushes the valve stem to accurately position the spool. For double-acting actuators, only two solenoid valves need to be added to control both chambers simultaneously [2].
The intelligent valve positioner adopts three-wire system and the power supply is 24 V DC. The human-computer interaction module includes a display and buttons, which are mainly used to display the working status and input working parameters of the positioner; external digital instructions can control the positioner to a certain extent. The main function is to ensure production safety; the valve position output is used to upload the real-time valve opening to the control center; the output alarm module can send an alarm signal when the positioner fails (3).
2 System design requirements 1) The positioning accuracy is within 0.5%, and the positioning accuracy does not change when the power supply voltage fluctuates by 10%.
2) Both manual and automatic operation modes are supported. Automatic operation is controlled by an external setting signal; manual operation is controlled by key operation.
3) Can adapt single/double acting actuators.
4) The set signal and valve position output signal are all 4-20 mA/0-20 mA/0-10 V/0-5 V optional.
5) With self-tuning function, through the self-tuning can determine the spool stroke range, the size of the actuator air chamber and cylinder friction and other parameters, and then determine the minimum intake air, adjust the PID parameters.
6) With self-diagnosis function, it can diagnose accidental power-down of setting signal, valve opening exceeding limit, excessive deviation, etc. When detecting a problem, it can protect the system and output alarm information at the same time [4].
7) Multiple flow characteristics (linear, equal percentage, fast opening, etc.) are optional, with split-range control.
8) The positioner can be simply controlled by an external digital command to open the valve to a preset safety position. 9) Password protection and Chinese/English switching function.
3 The system hardware is designed to reduce the interference between the analog ground and the digital ground. At the same time, the internal space of the positioner housing is fully utilized, and the hardware system is divided into two parts: the main control board and the interface board. Among them, the main control board includes MSP430 single-chip minimum system and human-computer interaction module; the interface board includes power supply circuit, sampling circuit, electrical conversion unit drive circuit, valve position output circuit and so on. The following describes each module separately.
3.1 Central Control Unit The central control unit is the core of the intelligent valve positioner. This system uses the Texas Instruments 54 series microcontroller MSP430F5438, an ultra-low power microprocessor with a 16-bit RISC architecture. The MSP430F5438 has five clock sources, 512 kB of FLASH ROM and 66 kB of RAM, 16-bit timers TimerA and TimerB with capture/comparator, 12-bit 8-channel ADC, and I2C, SPI, UART communication interface.
3.2 The power circuit positioner uses 24 V DC as the power supply. Because the voltage fluctuation in the industrial site is large, and the solenoid valve is driven by 24 V and sensitive to voltage fluctuations, the voltage of 24 V must be regulated. Power circuit design shown in Figure 2. U3 in the figure is a 24 V regulator module. According to the analysis of selected components, this system also requires two types of power supply, 5 V and 3.3 V. The LM1 is a 24 V to 5 V chip, and the LM2 is a 5 V to 3.3 V chip [5]. The system needs to output 24 V as an alarm signal, which is achieved by the optocoupler IC10 controlling the 24 V power supply; and it can input 15 to 30 V as an external digital command, first regulated by a Zener diode D7 to 3.3 V, and then through the optocoupler. After IC11 is isolated, it is input to the microcontroller pin.
3.3 analog signal sampling processing circuit 1) set the signal sampling and processing analog signal sampling processing circuit shown in Figure 3. The set signal requirements are 0-20 mA, 4-20 mA, 0-5 V, 0-10 V. The selection of the signal system is controlled through the P9.1 port. When P9.1 outputs high level, the optocoupler IC8 and IC9 are off. At this time, the voltage signal should be input. On the contrary, the current signal should be input, and the A/D converter of the microcontroller samples the voltage signal. Therefore, it needs to pass the sampling resistor. It is converted into a voltage signal.
2) Feedback signal sampling and processing Valve position feedback adopts high-precision conductive plastic displacement sensor. This article uses MSP430F5438 internal ADC programmable reference voltage (2.5 V) to supply the sensor. Op amp B forms a voltage follower whose output is adjusted by the displacement sensor. The voltage range of P6.3/A3 pins is 0 to 2.5 V.
3.4 Electrical Conversion Unit Drive Circuit The smart valve positioner's electrical conversion unit consists of four two-position three-way solenoid valves. Since the solenoid valve's supply voltage is 24 V and cannot be driven by the microcontroller pin, corresponding drive circuits must be designed. First, the optocoupler is driven through the I/O port of the microcontroller, then the transistor is driven by the optocoupler, and the last transistor drives the solenoid valve [6]. Electrical conversion unit drive circuit shown in Figure 4.
3.5 Valve position output circuit system requires real-time output of actual valve opening in the form of analog signal. The analog signal format is 0-20 mA, 4-20 mA, 0-5 V, 0-10 V. The actual opening of the valve is sampled by the controller through the displacement sensor and is set to a digital signal after being adjusted. The D/A is then converted into an analog signal, and finally the amplifier or V/I converts the output current. Because MSP430F5438 does not have D/A module, need to add D/A conversion chip DAC7611, the output voltage range of this chip is 0- 4 V; P9.0 is V/I change control end, when P9.0 is low level, IC5 IC6 is turned off and IC7 is turned on. At this time, the voltage signal is output and the voltage is amplified by amplifier A to more than 10 V. Conversely, when the current signal is output, the circuit first divides the D/A output value to obtain a voltage of 0 to 2 V, and then The V/I conversion circuit converts the current signal.
4 System software design The main task of the software design is to make difference between the collected set value and feedback value, according to the valve position control algorithm to generate the PWM wave control solenoid valve on and off to achieve the precise adjustment of the valve position. In addition, there is a need to implement additional features in the design requirements. Software design uses a modular design method, which makes the program structure clear, easy to write, debug, modify and later extend the function [7].
System functions are implemented by interrupts, mainly timer interrupts and key interrupts. The timer interrupt interval is 20 ms. The off-service program execution includes a control loop including a sampling program, a control algorithm program, and a PWM output program, which is the core of the entire software part; the interrupt priority of the key interrupt is higher than the timer interrupt, and the corresponding execution is performed in the interrupt service program. Key operation [8].
The main program flow chart shown in Figure 6. After the system is powered on, it first initializes each module, and then turns on the total interrupt and enters an infinite loop. The large loop includes the LCD display program, external digital command processing program, self-tuning program, self-diagnostic program, and valve position output program.
This program contains the entire control closed loop, and the sampling interval is 20 ms. First, the 12-bit ADC provided by the MSP430F5438 microcontroller samples the setpoint and feedback values. In order to reduce the sampling point high-frequency interference, the median filtering method is used in the program: 12 data are collected, the highest and lowest values ​​are removed, and the average value is taken as a sampling value [9]. Next, set values ​​and feedback values ​​are normalized separately, and the two are unified within a range of 0 to 100%, which facilitates subsequent processing. Then according to the need to implement the corresponding flow characteristics and split control functions, including flow characteristics including linear, fast on and equal percentages. Faster and equal percentages also have multiple curves, and even users can customize the shape of the curve. After the deviation is found, the fuzzy PID control algorithm is executed to output the PWM wave to drive the solenoid valve, and the fuzzy control is used to set the PID parameters [10?11], which is very suitable for this kind of nonlinear system. Key interrupt flow chart shown in Figure 8. All operations on the locator are achieved through four separate keys, which are the OK key, the up key, the down key, and the exit key. In the main interface, press the OK button for 3 s to switch between manual operation and automatic operation [12]. Press the up/down button for 3 s to open the menu. After entering the menu, the OK key can enter the selected sub-menu or perform a selected function, and the up/down keys can scroll the menu. The up/down keys can be used to set the opening degree of the valve in the manual operation mode, and the appropriate parameters can be adjusted during parameter adjustment. The exit key can directly exit the current operation in any state and return to the main interface. In addition, the locator also has a password protection function to ensure the safety of the production process; with Chinese and English switching capabilities, is conducive to go abroad to sell overseas; has a trip limit function.
5 experimental and analytical experimental platform as shown in Figure 9. In the figure, the circular board is the main control board; the square board is the interface board; the middle LCD display and the following four keys constitute the human-computer interaction module; the lower left corner is the solenoid valve; the lower right corner is the signal generator, which can generate 4-20 mA signal Used as an input; the upper is a single-acting regulating valve and a displacement sensor is mounted on the regulating valve.
The on-site commissioning of the entire system, air pressure of 7.0 MPa, was stabilized to 5.0 MPa by the pressure reducing valve. First of all, a self-tuning is performed to determine the relevant parameters. The actuator selects a single action and the signal system selects 4-20 mA. After verifying each additional function, its control performance is tested, and the valve is opened from the closed position to the opening degree of 25%, 50%, and 75% in turn every 15 seconds, and then the opening degree is successively reduced to close. According to the measured data plotted control curve shown in Figure 10. It can be seen that the positioner is adjusted very quickly, the adjustment time is within 5 s, and the control accuracy is within 0.5%. The power supply voltage was raised to 26.4 V and dropped to 21.6 V. Two sets of tests were performed and similar results were obtained, indicating that the control effect was unchanged within 10% of the power supply fluctuation.
6 Conclusions A multi-functional intelligent valve positioner has been designed in this paper. The system software and hardware configuration are described in detail. After testing, the system functions are normal and the control effect meets the requirements. The work accomplished by the author achieves the desired goal. The designed intelligent valve positioner can be widely applied to the actual system, with low cost and high reliability, and can obtain considerable economic benefits.
References [1] Wang Zaiying, Liu Huaixia, Chen Yijing. Process Control System and Instrumentation [M]. Beijing: Mechanical Industry Press, 2006.
WANG Zaiying, LIU Huaixia, CHEN Yijing. Process control system and instrument [M]. Beijing: China Machine Press, 2006.
[2] Shang Qunli, Jiang Peng.Development of intelligent electric valve positioner[J]. Chinese Journal of Scientific Instrument,2007,28(4):718?721.
SHANG Qunli, JIANG Peng, Research on intelligent electro?pneumatic valve positioner[J]. Chinese Journal of Scientific Instruments, 2007, 28(4): 718?721.
[3] YUZAWA S, OOTSUKA K, NAGATA M, et al. New smart valve positioner with advanced diagnostics for enhanced safety of plant operations [C]// Proceedings of 54th Annual Conference of the Society of Instrument and Control Engineers of Japan. : IEEE, 2015: 1023?1028.
[4] Wang Hongqing. Design of intelligent valve positioner control system based on micro controller[J]. Instrument Technology and Sensors, 2010(10):92?94.
WANG Hongqing. Design of intelligent valve locator control system based on MCU [J]. Instrument technique and sensor, 2010(10): 92?94.
[5] Lin Hui. Research and development of intelligent electric valve positioner [D]. Tianjin: Tianjin University, 2003.
LIN Hui. Research and development on smart electrical valve positioner [D]. Tianjin: Tianjin University, 2003.
[6] YU Wei, DONG Quanlin, ZHANG Yulian, et al. Research on valve position intelligent adjustment measurement and control system based on MSP430 microcontroller[J]. Modern Electronic Technology, 2015, 38(23):94?97.
YU Wei, DONG Quanlin, ZHANG Yulian, et al. Study on MSP430 SCM based measurement and control system of valve intelligent regulation [J]. Modern electronics technique, 2015, 38(23): 94?97.
[7] Cai Ming, Bai Xuelian, Zhang Ying. The design of a new domestic intelligent valve positioner[J]. Automation Instrumentation, 2011, 32(7): 73?75.
CAI Ming, BAI Xuelian, ZHANG Ying. Design of new type of domestic smart valve positioner[J]. Process Automation Instrumentation, 2011, 32(7): 73?75.
[8] Liu Huisen, Dong Quanlin, Ding Ying, et al. Research on smart valve positioner based on HART protocol[J]. Modern Electronic Technology, 2016, 39(15):160?163.
LIU Huisen, DONG Quanlin, DING Ying, et al. Study on intelligent valve positioner based on HART protocol [J]. Modern electronics technique, 2016, 39(15): 160?163.
[9] Bao He, Hu Endian, Zhou Peng, et al. Development of low-power valve positioner for power plant[J]. Hydraulic and Pneumatic, 2016(6):78?83.
BAO He, HU Endian, ZHOU Peng, et al. Development of low power valve positioner for power plant [J]. Chinese hydraulics & pneumatics, 2016(6): 78?83.
[10] Li Pengxian. Development of intelligent valve positioner [D]. Chongqing: Chongqing University of Technology, 2014.
LI Pengxian. Development of intelligent valve positioner [D]. Chongqing: Chongqing University of Technology, 2014.
[11] Zhao Mingnan, Yang Jintang, Xia Zhongyu, et al. Research on control method of intelligent valve positioner[J]. Machine Tools & Hydraulics, 2015, 43(2):141?144.
ZHAO Mingnan, YANG Jintang, XIA Zhongyu, et al. Research on the intelligent valve positioner control method [J]. Machine tool & Hydraulics, 2015, 43(2): 141?144.
[12] Li Ming, Zhou Tianlong, Huang Xiaogang. Intelligent Valve Positioner Design Based on PROFIBUS?DP[J]. Instrument Technology and Sensors, 2011(2): 71?73.
LI Ming, ZHOU Tianlong, HUANG Xiaogang. Design of intelligent valve positioner based on PROFIBUS?DP [J]. Instrument technique and sensor, 2011(2): 71?73.
Key words: smart valve positioner; hardware design; software design; solenoid valve; fuzzy control ?05
Abstract: In allusion to the control precision and stability requirements of the regulating valve in the industrial control field, an intelligent valve positioner based on MSP430 SCM is designed. In the positioner, MSP430F5438 is used as the core controller, the high?speed switching solenoid The valve is selected for the execution unit, and the fuzzy control is used in the control algorithm to tune the PID parameters. In addition to the function of accurate positioning, the positioner also has various auxiliary functions such as self?tuning, self?diagnosis and The experimental results show that the system has the characteristics such as high control precision and stability. , rich functions, high intellectualized degree, and easy maintenance.
Keywords: intelligent valve positioner; MSP430F5438; hardware design; software design; solenoid valve; fuzzy control
Valve positioner is an important instrument in the field of industrial process control. It has been widely used in petrochemical, water conservancy, metallurgy and other industries [1]. Due to the gap in related technology, the domestic market has been dominated by large foreign companies. In order to revitalize the national industry, this article has developed a high-performance intelligent valve positioner based on MSP430 microcontroller, which has complete functions and good positioning effect.
1 System Design Principle Figure 1 shows the basic structure of a smart valve positioning system. The system will convert the 4-20 mA (or other signal system) setting signal into a digital signal and send it to the microprocessor. At the same time, the valve opening information will be converted back to the microprocessor through the displacement sensor. The microprocessor will make the difference between the two signals. If the deviation is in the dead zone range, the two switch solenoid valves will be in the cut-off state; otherwise, the corresponding PWM control signal will be controlled by the valve position control algorithm according to the size of the deviation. The two solenoid valves are turned off. In this way, the actuator's compressed air flow is adjusted, which in turn pushes the valve stem to accurately position the spool. For double-acting actuators, only two solenoid valves need to be added to control both chambers simultaneously [2].
The intelligent valve positioner adopts three-wire system and the power supply is 24 V DC. The human-computer interaction module includes a display and buttons, which are mainly used to display the working status and input working parameters of the positioner; external digital instructions can control the positioner to a certain extent. The main function is to ensure production safety; the valve position output is used to upload the real-time valve opening to the control center; the output alarm module can send an alarm signal when the positioner fails (3).
2 System design requirements 1) The positioning accuracy is within 0.5%, and the positioning accuracy does not change when the power supply voltage fluctuates by 10%.
2) Both manual and automatic operation modes are supported. Automatic operation is controlled by an external setting signal; manual operation is controlled by key operation.
3) Can adapt single/double acting actuators.
4) The set signal and valve position output signal are all 4-20 mA/0-20 mA/0-10 V/0-5 V optional.
5) With self-tuning function, through the self-tuning can determine the spool stroke range, the size of the actuator air chamber and cylinder friction and other parameters, and then determine the minimum intake air, adjust the PID parameters.
6) With self-diagnosis function, it can diagnose accidental power-down of setting signal, valve opening exceeding limit, excessive deviation, etc. When detecting a problem, it can protect the system and output alarm information at the same time [4].
7) Multiple flow characteristics (linear, equal percentage, fast opening, etc.) are optional, with split-range control.
8) The positioner can be simply controlled by an external digital command to open the valve to a preset safety position. 9) Password protection and Chinese/English switching function.
3 The system hardware is designed to reduce the interference between the analog ground and the digital ground. At the same time, the internal space of the positioner housing is fully utilized, and the hardware system is divided into two parts: the main control board and the interface board. Among them, the main control board includes MSP430 single-chip minimum system and human-computer interaction module; the interface board includes power supply circuit, sampling circuit, electrical conversion unit drive circuit, valve position output circuit and so on. The following describes each module separately.
3.1 Central Control Unit The central control unit is the core of the intelligent valve positioner. This system uses the Texas Instruments 54 series microcontroller MSP430F5438, an ultra-low power microprocessor with a 16-bit RISC architecture. The MSP430F5438 has five clock sources, 512 kB of FLASH ROM and 66 kB of RAM, 16-bit timers TimerA and TimerB with capture/comparator, 12-bit 8-channel ADC, and I2C, SPI, UART communication interface.
3.2 The power circuit positioner uses 24 V DC as the power supply. Because the voltage fluctuation in the industrial site is large, and the solenoid valve is driven by 24 V and sensitive to voltage fluctuations, the voltage of 24 V must be regulated. Power circuit design shown in Figure 2. U3 in the figure is a 24 V regulator module. According to the analysis of selected components, this system also requires two types of power supply, 5 V and 3.3 V. The LM1 is a 24 V to 5 V chip, and the LM2 is a 5 V to 3.3 V chip [5]. The system needs to output 24 V as an alarm signal, which is achieved by the optocoupler IC10 controlling the 24 V power supply; and it can input 15 to 30 V as an external digital command, first regulated by a Zener diode D7 to 3.3 V, and then through the optocoupler. After IC11 is isolated, it is input to the microcontroller pin.
3.3 analog signal sampling processing circuit 1) set the signal sampling and processing analog signal sampling processing circuit shown in Figure 3. The set signal requirements are 0-20 mA, 4-20 mA, 0-5 V, 0-10 V. The selection of the signal system is controlled through the P9.1 port. When P9.1 outputs high level, the optocoupler IC8 and IC9 are off. At this time, the voltage signal should be input. On the contrary, the current signal should be input, and the A/D converter of the microcontroller samples the voltage signal. Therefore, it needs to pass the sampling resistor. It is converted into a voltage signal.
2) Feedback signal sampling and processing Valve position feedback adopts high-precision conductive plastic displacement sensor. This article uses MSP430F5438 internal ADC programmable reference voltage (2.5 V) to supply the sensor. Op amp B forms a voltage follower whose output is adjusted by the displacement sensor. The voltage range of P6.3/A3 pins is 0 to 2.5 V.
3.4 Electrical Conversion Unit Drive Circuit The smart valve positioner's electrical conversion unit consists of four two-position three-way solenoid valves. Since the solenoid valve's supply voltage is 24 V and cannot be driven by the microcontroller pin, corresponding drive circuits must be designed. First, the optocoupler is driven through the I/O port of the microcontroller, then the transistor is driven by the optocoupler, and the last transistor drives the solenoid valve [6]. Electrical conversion unit drive circuit shown in Figure 4.
3.5 Valve position output circuit system requires real-time output of actual valve opening in the form of analog signal. The analog signal format is 0-20 mA, 4-20 mA, 0-5 V, 0-10 V. The actual opening of the valve is sampled by the controller through the displacement sensor and is set to a digital signal after being adjusted. The D/A is then converted into an analog signal, and finally the amplifier or V/I converts the output current. Because MSP430F5438 does not have D/A module, need to add D/A conversion chip DAC7611, the output voltage range of this chip is 0- 4 V; P9.0 is V/I change control end, when P9.0 is low level, IC5 IC6 is turned off and IC7 is turned on. At this time, the voltage signal is output and the voltage is amplified by amplifier A to more than 10 V. Conversely, when the current signal is output, the circuit first divides the D/A output value to obtain a voltage of 0 to 2 V, and then The V/I conversion circuit converts the current signal.
4 System software design The main task of the software design is to make difference between the collected set value and feedback value, according to the valve position control algorithm to generate the PWM wave control solenoid valve on and off to achieve the precise adjustment of the valve position. In addition, there is a need to implement additional features in the design requirements. Software design uses a modular design method, which makes the program structure clear, easy to write, debug, modify and later extend the function [7].
System functions are implemented by interrupts, mainly timer interrupts and key interrupts. The timer interrupt interval is 20 ms. The off-service program execution includes a control loop including a sampling program, a control algorithm program, and a PWM output program, which is the core of the entire software part; the interrupt priority of the key interrupt is higher than the timer interrupt, and the corresponding execution is performed in the interrupt service program. Key operation [8].
The main program flow chart shown in Figure 6. After the system is powered on, it first initializes each module, and then turns on the total interrupt and enters an infinite loop. The large loop includes the LCD display program, external digital command processing program, self-tuning program, self-diagnostic program, and valve position output program.
This program contains the entire control closed loop, and the sampling interval is 20 ms. First, the 12-bit ADC provided by the MSP430F5438 microcontroller samples the setpoint and feedback values. In order to reduce the sampling point high-frequency interference, the median filtering method is used in the program: 12 data are collected, the highest and lowest values ​​are removed, and the average value is taken as a sampling value [9]. Next, set values ​​and feedback values ​​are normalized separately, and the two are unified within a range of 0 to 100%, which facilitates subsequent processing. Then according to the need to implement the corresponding flow characteristics and split control functions, including flow characteristics including linear, fast on and equal percentages. Faster and equal percentages also have multiple curves, and even users can customize the shape of the curve. After the deviation is found, the fuzzy PID control algorithm is executed to output the PWM wave to drive the solenoid valve, and the fuzzy control is used to set the PID parameters [10?11], which is very suitable for this kind of nonlinear system. Key interrupt flow chart shown in Figure 8. All operations on the locator are achieved through four separate keys, which are the OK key, the up key, the down key, and the exit key. In the main interface, press the OK button for 3 s to switch between manual operation and automatic operation [12]. Press the up/down button for 3 s to open the menu. After entering the menu, the OK key can enter the selected sub-menu or perform a selected function, and the up/down keys can scroll the menu. The up/down keys can be used to set the opening degree of the valve in the manual operation mode, and the appropriate parameters can be adjusted during parameter adjustment. The exit key can directly exit the current operation in any state and return to the main interface. In addition, the locator also has a password protection function to ensure the safety of the production process; with Chinese and English switching capabilities, is conducive to go abroad to sell overseas; has a trip limit function.
5 experimental and analytical experimental platform as shown in Figure 9. In the figure, the circular board is the main control board; the square board is the interface board; the middle LCD display and the following four keys constitute the human-computer interaction module; the lower left corner is the solenoid valve; the lower right corner is the signal generator, which can generate 4-20 mA signal Used as an input; the upper is a single-acting regulating valve and a displacement sensor is mounted on the regulating valve.
The on-site commissioning of the entire system, air pressure of 7.0 MPa, was stabilized to 5.0 MPa by the pressure reducing valve. First of all, a self-tuning is performed to determine the relevant parameters. The actuator selects a single action and the signal system selects 4-20 mA. After verifying each additional function, its control performance is tested, and the valve is opened from the closed position to the opening degree of 25%, 50%, and 75% in turn every 15 seconds, and then the opening degree is successively reduced to close. According to the measured data plotted control curve shown in Figure 10. It can be seen that the positioner is adjusted very quickly, the adjustment time is within 5 s, and the control accuracy is within 0.5%. The power supply voltage was raised to 26.4 V and dropped to 21.6 V. Two sets of tests were performed and similar results were obtained, indicating that the control effect was unchanged within 10% of the power supply fluctuation.
6 Conclusions A multi-functional intelligent valve positioner has been designed in this paper. The system software and hardware configuration are described in detail. After testing, the system functions are normal and the control effect meets the requirements. The work accomplished by the author achieves the desired goal. The designed intelligent valve positioner can be widely applied to the actual system, with low cost and high reliability, and can obtain considerable economic benefits.
References [1] Wang Zaiying, Liu Huaixia, Chen Yijing. Process Control System and Instrumentation [M]. Beijing: Mechanical Industry Press, 2006.
WANG Zaiying, LIU Huaixia, CHEN Yijing. Process control system and instrument [M]. Beijing: China Machine Press, 2006.
[2] Shang Qunli, Jiang Peng.Development of intelligent electric valve positioner[J]. Chinese Journal of Scientific Instrument,2007,28(4):718?721.
SHANG Qunli, JIANG Peng, Research on intelligent electro?pneumatic valve positioner[J]. Chinese Journal of Scientific Instruments, 2007, 28(4): 718?721.
[3] YUZAWA S, OOTSUKA K, NAGATA M, et al. New smart valve positioner with advanced diagnostics for enhanced safety of plant operations [C]// Proceedings of 54th Annual Conference of the Society of Instrument and Control Engineers of Japan. : IEEE, 2015: 1023?1028.
[4] Wang Hongqing. Design of intelligent valve positioner control system based on micro controller[J]. Instrument Technology and Sensors, 2010(10):92?94.
WANG Hongqing. Design of intelligent valve locator control system based on MCU [J]. Instrument technique and sensor, 2010(10): 92?94.
[5] Lin Hui. Research and development of intelligent electric valve positioner [D]. Tianjin: Tianjin University, 2003.
LIN Hui. Research and development on smart electrical valve positioner [D]. Tianjin: Tianjin University, 2003.
[6] YU Wei, DONG Quanlin, ZHANG Yulian, et al. Research on valve position intelligent adjustment measurement and control system based on MSP430 microcontroller[J]. Modern Electronic Technology, 2015, 38(23):94?97.
YU Wei, DONG Quanlin, ZHANG Yulian, et al. Study on MSP430 SCM based measurement and control system of valve intelligent regulation [J]. Modern electronics technique, 2015, 38(23): 94?97.
[7] Cai Ming, Bai Xuelian, Zhang Ying. The design of a new domestic intelligent valve positioner[J]. Automation Instrumentation, 2011, 32(7): 73?75.
CAI Ming, BAI Xuelian, ZHANG Ying. Design of new type of domestic smart valve positioner[J]. Process Automation Instrumentation, 2011, 32(7): 73?75.
[8] Liu Huisen, Dong Quanlin, Ding Ying, et al. Research on smart valve positioner based on HART protocol[J]. Modern Electronic Technology, 2016, 39(15):160?163.
LIU Huisen, DONG Quanlin, DING Ying, et al. Study on intelligent valve positioner based on HART protocol [J]. Modern electronics technique, 2016, 39(15): 160?163.
[9] Bao He, Hu Endian, Zhou Peng, et al. Development of low-power valve positioner for power plant[J]. Hydraulic and Pneumatic, 2016(6):78?83.
BAO He, HU Endian, ZHOU Peng, et al. Development of low power valve positioner for power plant [J]. Chinese hydraulics & pneumatics, 2016(6): 78?83.
[10] Li Pengxian. Development of intelligent valve positioner [D]. Chongqing: Chongqing University of Technology, 2014.
LI Pengxian. Development of intelligent valve positioner [D]. Chongqing: Chongqing University of Technology, 2014.
[11] Zhao Mingnan, Yang Jintang, Xia Zhongyu, et al. Research on control method of intelligent valve positioner[J]. Machine Tools & Hydraulics, 2015, 43(2):141?144.
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