Abstract: In the past two decades, with the continuous development of electrical control and microprocessor technology, the electrical control technology of valve actuators has entered a stage of rapid development, from the ordinary type of electric actuators that were originally based on mechanical components and simple electrical components. The organization has developed into an intelligent electric actuator that is dominated by non-intrusive electrical control systems using single-chip microcomputer technology, and has gradually developed an intelligent electric actuator. In this transition process, the application of microcontroller technology has played a key role. The article focuses on the gradual application, rapid development, and future direction of single-chip microcomputer technology during the development of the control system of valve electric actuators in the past two decades.
Keywords: single-chip computer; valve electric actuator; application; development direction.
Abstract: In the past twenty years, with the development of electrical control and microprocessor technology, the electric control technology of electric actuator of valve has entered a rapid development stage. By the mechanical components and simple electrical components based on the common type of electric actuator , to the application of single-chip microcomputer technology of non-invasive electrical control system as the dominant position of the intelligent electric actuator. And temporarily develop into intelligent electric actuator. In this process of transformation, the application of single-chip technology plays a Key role. This paper focuses on the application, rapid development and future direction of single-chip microcomputer technology in the research and development of electric valve actuator control system in the past twenty years.
Keywords: single chip microcomputer; valve electric actuator; application; development direction
Introduction Valve actuators are commonly used to drive valves in industrial control. They are electromechanical devices that convert electrical energy into mechanical displacement. They use electrical energy as a power source to receive control signals from the control system (switch, analog, and bus signals). ), drive the valve to open, close or run to a certain position, can be used for opening, closing and positioning control of various valves (regulating valves, gate valves, ball valves, globe valves, etc.) in the industrial field, widely used in thermal power, chemical industry, Steel and environmental protection industries.
Microcontroller (MCU) is a programmable device that integrates hardware such as central processing unit CPU, data memory RAM, program memory ROM, and input/output I/O into a single chip. After the corresponding software programming, the functions that can be realized with very complicated analog and digital circuits can be completed.
Before the 1990s, the electric actuators for valves were mainly based on mechanical components. Later, with the development of electric control technology, more and more applications of the single-chip microcomputer technology were being implemented in actuators, and the implementing agencies gradually developed into non-invasive designs. Smart, and ultimately to a smarter development with more powerful features. The application of SCM technology plays an indispensable role in the upgrading of actuator products.
The application of single-chip microcomputer technology in valve electric actuators can be divided into the following three stages:
Early application stage: In the 1990s, with the continuous development, popularization and application of single-chip microcomputer technology, microprocessor technology began to be used in the production process of industrial automation products. In the design of automated instrumentation, R&D personnel broke the original design thinking and switched from the traditional analog electronic circuit design to the microcontroller-based controller design, thereby simplifying the circuit, improving the reliability and stability of the instrument, and reducing the cost. Accelerated the replacement of products and solved the problems of many traditional instruments. Among them, the regulating valve electric actuator is a typical representative of this stage.
High-speed development stage: From the late 1990s to 2010, with the emergence of the SOC (System On Chip) platform, MCU technology has developed rapidly. Enhanced 8-bit microcontrollers that run faster and have higher integration have emerged in an endless stream. The technological revolution has laid a solid foundation for the implementation of major breakthroughs in the electrical control system. Under the leadership of leading foreign companies, there have emerged a number of non-intrusive smart products with liquid crystal display, infrared remote control, absolute coding and fieldbus and many other latest control technologies.
The stage of comprehensive innovation: After 2010, with the further development of smart sensor technology, Internet of things technology and CPU technology, 32-bit ARM processors such as CM3 have appeared for the SCM market. At this time, the valve electric actuators have entered the stage of comprehensive innovation for smart development. Intelligent sensing, intelligent decision making, big data, internet of things, and cloud technology have become the main directions of development. Smart valve actuators have gradually become the future direction of the executive agency industry.
1 The composition of the valve electric actuator The valve actuator generally consists of three parts, namely:
Motor: As shown in part 11 of Figure 1. Convert electrical energy into mechanical displacement to power actuators.
Mechanical transmission part: as shown in part 1, 2, 3, 5, 6, 7, 8, 9, 10 of Fig. 1. Through the deceleration transmission, the high speed and low torque generated by the rotation of the motor is converted into the low speed and high torque output by the actuator, and the valve switching operation is driven through the mechanical interface and the valve connection. Electrical control system: as shown in part 4 of Figure 1. The control system is the core part of the implementing agency. After receiving the on-site and remote operating instructions, the motor is driven and the actuator status signal is output after the logical operation based on the collected actuator's own status.
2 The early application stage of the single-chip microcomputer technology in the actuator The control principle of the early valve electric actuator is relatively simple. The mechanical limit controller and the torque controller are used to achieve the valve's switch limit control and over-torque protection, through the control box. To achieve open and close operation control. According to the different control methods, it can be divided into two types: switch type and regulation type. The switch type mainly receives the switch signal of the control system. Under normal circumstances, it operates in the fully open and fully closed positions. The adjustment type mainly receives the analog signal of the control system, and can continuously position the valve according to the analog quantity to drive the valve to any position.
Adjustable electric actuators essentially belong to the DDZ-III type instrument, and use 4 to 20mA of analog quantity to control the valve opening, and continuously position according to the analog signal. The traditional design method is to use a servo amplifier to compare the analog signal given by the control system with the valve position signal of the actuator. When the difference between the two is greater than the dead zone, the control motor drives the actuator to reduce the difference. The direction of operation. However, servo amplifiers are mostly analog circuits and have inherent defects such as difficulty in debugging, zero drift, temperature drift, and poor anti-interference ability. In addition, many components, large size, high cost, and many points of failure require a better solution. .
At that time, the single-chip microcomputer technology had not been widely used, and the scope of the selection was also very narrow. There were Intel's 8031, 8051 series; Motorola's 6800 series; Microchip's PIC series; Atmel's AT89C52, AT89C2051 and so on. Among them, because of AT89C2051, with built-in EEPROM, easy programming and debugging, more data, low cost, the number of I / O ports can meet the initial requirements of the adjustment control system design, so it is selected and some peripheral devices constitute a regulating type electric execution Institutional control system. Control system mainly consists of: AT 89C2051, linear power supply, AD conversion chip TLC0834, reset chip IMP813L and two-way valve position transmitter BS-2, hardware system block diagram shown in Figure 2.
The software was only written in assembly language at the time, and the programming and modification were relatively difficult. After the HEX file is compiled and generated by ASM51, it is programmed by a dedicated programmer. Figure 3 shows the software flowchart and assembly language program fragments using AT89C2051.
Although the early application of SCM technology now looks too primitive and simple, the designers of the actuators at that time changed the original design thinking and framework, from the traditional analog electronic circuit design to the SCM as the core, plus the control of independent peripheral chips. Device design changes. Because it is an early product, there are problems such as small program memory, no on-chip non-volatile data memory, complicated instruction and timing, no integrated peripherals, less I/O ports, and poor anti-interference ability. All these increase. The designer's difficulties.
3 The high-speed development stage of the application By the mid-1990s, the 8051 family of microcontrollers was mainly manufactured by companies such as Silicon Labs, Atmel, and Philips, and its performance and functionality were greatly improved on the basis of compatibility with the 8051 microcontroller. Such as: improving the timing characteristics of instructions to improve the operating speed, increase the integration of peripherals to improve system integration, ease the dynamic range of the power supply voltage, and enhance anti-jamming capabilities. Later, Analog Devices, Silicon Labs, and Atmel launched the ADUC812, C8051F, and AVR series of mixed-signal microcontrollers, and proposed the concept of the SOC (System On Chip) platform. Microcontrollers with this type of platform are also known as enhanced 8-bit MCUs. These MCUs all have a high-speed pipeline (RISC) instruction structure, have an 8051-compatible core, and have a large number of I/O interfaces, multiple independent built-in A/D and D/A channels, nonvolatile data memory EEPROM Internal R/C oscillator. Integrating a hardware system function on a single chip provides great convenience to R&D personnel and makes system integration even higher.
At the same time, the electric actuators for valves at this stage introduced many new control technologies under the guidance of some foreign brands. Such as: non-invasive design, free from the box debugging, using an absolute coded stroke controller to replace the mechanical stroke controller, push-pull torque sensor, wireless remote control and fieldbus. The implementing agency entered the intelligent non-intrusive application stage. However, these control technologies put higher requirements on the number of MCUs, the types of integrated peripherals, and the operating speed to a certain extent. The original traditional single-chip microcomputers cannot meet the requirements, and the MCUs with the SOC concept are obviously in good agreement. New design requirements.
After comparison, this paper selected C8051F020 in Silicon Labs' C8051F series and ATmega64 in Atmel's AVR series, which were applied to the SND and SND3 series intelligent valve electric actuators proposed in this paper. Both MCUs have more than 50 I/O ports and a variety of analog digital peripherals; both use RSIC-based reduced instruction sets and pipelined technology to speed up program execution; all have 64K or more FLASH and several non-volatile Memory, to meet the requirements of program storage and data storage. Among them ATmega64 still has the characteristic of low power consumption and wide voltage, can improve the EMC characteristic of the system. Figure 4 is a block diagram of an enhanced 8-bit MCU hardware system. As can be seen from the figure, a chip can complete the design of the actuator control system without adding peripherals, simplifying the design of the hardware system and improving reliability.
The software part is written in C language. After the C8051F020 is written and compiled by Keil uVision2 software, it is written to the microcontroller with a Silicon dedicated programmer. After the ATmega64 is written and compiled by ICCAVR, it is written to the microcontroller through a dedicated programmer using AVR Studio 4.0. Figure 5 shows the software flowchart of ATmega64 and some of the C language programs.
After the electric actuator of the valve enters this stage, the application requirements of the control system to the field bus are more and more, mainly based on bus types such as Profibus-DP, Modbus-RTU, and CANBUS. Based on the establishment of the SOC platform, these fieldbuses can easily design various bus interfaces through the UART port, protocol chip, and bus interface chip. For example Profibus-DP bus, as long as through the DP bus protocol chip SPC3 and RS485 driver chip ADM2486, you can achieve the bus slave hardware system. Then, a software program written according to the relevant information can be connected to the fieldbus network.
However, in the late stage of the rapid development of valve electric actuators, the SOC platform has gradually appeared insufficient in terms of functions such as low power consumption (battery applications), storage space, real-time clock, network and communication (Ethernet interface), and new developments are needed. More high-performance processors to solve the problems. 4 Overall Innovation Phase of Application After 2010, many high-end users have put forward new requirements for smart actuators, such as:
In the absence of AC external power supply, the actuator is required to display the valve position on the LCD screen.
The implementing agency is required to have a data recording function to facilitate the rapid data analysis and fault diagnosis of the system.
The actuator is required to be able to collect some diagnostic data and process parameters of valves and pipes as field devices.
The interior of the actuator must detect environmental parameters such as temperature, voltage, and vibration.
At the same time, the Internet, Internet of Things, and cloud technologies are increasingly used in industrial products. Implementing agencies can use these technologies to implement functions such as remote control and remote data acquisition and analysis.
However, the executive agency design industry also put forward the concept of intelligent electric actuators, including:
Depth perception: Perceive the working status (vibration, torque) of pipes and valves.
Intelligent decision making: The on-site programming, recording data, and troubleshooting can determine the behavior of the actuator.
Precise execution: high-speed operation, high-precision positioning, high-precision torque detection technology.
Simple and exquisite: The structure of the implementing agency has become more compact, smaller, more powerful, and more manipulative.
Given the background of industry and technology development, the original control system has been difficult to meet new requirements in terms of operating speed, storage space, power consumption, and types of peripherals. Therefore, the intelligent valve electric actuators using the ARM platform control system were gradually developed.
The electrical control system of the intelligent valve electric actuator adopts an ARM-based 32-bit processor: CortexTM-M3 CPU (STM32F205/207). Its 32-bit instruction system has 32-bit data processing capabilities. Compared to any 8-bit MCU, it greatly improves the performance of the control system, including increased operating speed, enhanced processing capabilities, increased storage capacity, and increased scalability. , significantly reduce power consumption.
STM32F205/207 microprocessor with high-performance ARM 32-bit RISC core, operating frequency up to 120MHz; internal contains high-speed memory (up to 1MByte of flash memory, 128KByte of SRAM and 4K spare SRAM); rich enhanced I / O Port with peripherals connected to two APB buses, 3 AHB buses and a 32-bit multi-AHB bus matrix, 3 12-bit ADCs and 2 DACs (valve setting for actuators and Feedback), 1 low-power RTC (for running data logging), 12 universal 16-bit timers (including 2 PWM timers for motor control), 2 general-purpose 32-bit timers, A true random number generator RNG (used to generate the serial number); the newly added advanced peripherals include 1 SDIO and 1 FSMC interface (for expansion of the executive's memory space), 1 USB OTG interface (makes The historical data of the actuator can be directly downloaded), 4 USART interfaces and 2 UART interfaces (for expansion of various fieldbuses); other standard peripherals also include: 3 I2C interfaces, 3 SPI interfaces, 2 I2S Interface and 2 CAN interfaces and so on, resources are very rich. In addition, the chip also has a dedicated battery pin for RTC power supply, in the STM32F207 also has Ethernet and camera interface, and TCP / IP network connection, can expand the Internet of things, the Internet and cloud technology and other functions. The operating temperature range of the chip is -40°C to +105°C, which can meet the requirements of most industrial sites; the operating voltage range is 2.0V to 3.6V, and the minimum power consumption is less than 3uA, which can significantly extend the built-in lithium battery The use of time.
ARM-based 32-bit processors are ideally suited to the use of intelligent valve actuators for industrial field devices in the core, instruction systems, memory capacity and scalability, type and number of peripherals, power consumption, and operating temperature range. Figure 6 shows a block diagram of an ARM-based hardware system.
As can be seen from Fig. 6, on the basis of retaining the advantages of the enhanced 8-bit MCU, the ARM processor also adds many new technologies and new functions to the actuator, such as low-power battery application technology, wireless data transmission technology, and sensor integration technology. , cloud technology, and data record storage capabilities.
In the new application phase, some of the leading brands in the industry, such as German and British actuator manufacturers, have used one or more STM32F series processors in their new series of electric actuators, adding many The new function further enhances the performance of the actuator and opens the concept of a smart valve actuator. Manufacturers of domestic implementing agencies have also launched related products one after another. The valve electric actuators will enter a new stage under the leadership of 32-bit ARM technology.
5 Concluding remarks This article describes the gradual application process of microcontroller technology in the valve electric actuator from scratch, from the early stage of initial application, to the later stage of high-speed development, and to the current stage of comprehensive innovation. Throughout the entire process, the implementing agencies have also gone through the process of upgrading from general regulation, development to intelligence, and finally to intelligence; the development and application of single-chip microcomputer technology to promote the replacement of valve actuators and actuators industry technology The improvement of the level plays a crucial role. The electric actuator of the valve is the most end of the industrial automation system and an indispensable part of industrial process control. Its technological advancement helps to improve the overall level of industrial automation in China.
references:
[1]Ren Yang. Research on frequency conversion speed regulation in the control part of intelligent electric actuator[J].Science,2012(7):226-226.
[2]Chi Haodong. Design of control system for electric actuator [D]. Xidian University, 2015.
[3] Dong Qiwei. Research on electric actuator controller based on full electronic torque protection [D]. Shandong University, 2015.
[4] Li Zhi. Research on intelligent controller of valve electric actuator based on switched reluctance motor [D]. Jiangsu University, 2008.
[5] Xu Mingyao. Research on a switched reluctance speed-regulating valve electric actuator mechanical control system based on TMS320F28335 [D]. Jiangsu University, 2013.
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