Systematic Exploration of Vacuum Intelligent Vacuum Measurement and Control Instrumentation Kang Qiang (Taizhou Metrology and Measurement Technology Research Institute, Taizhou, Jiangsu 225300, China) The engineering significance of intelligent instrumentation explains the design principle of this systematic vacuum instrument and introduces the ZKY-50B intelligence. The design points of multi-parameter measurement and control instrument for vacuum system and its application in vacuum freeze-drying system control.
1 The purpose and significance of the vacuum system multi-parameter measurement and control instrument In recent years, with the successful application of vacuum technology, the vacuum application system has become more and more important in many industrial fields and scientific research fields, in the electronic space, information, and biological engineering. This is especially true in high-tech areas. The new vacuum application system continues to emerge, placing higher requirements on vacuum monitoring and control instruments. In addition, due to the development of computer technology, it provides a more powerful embedded microprocessor chip, so with a high-performance embedded microprocessor (MCU For the core of the instrument, a systematic multi-parameter process control instrument suitable for small and medium-sized vacuum application engineering is designed, which is not only a market demand but also technically possible.
The vacuum application system is actually using a special low-pressure, high-purification space provided by vacuum technology to obtain a new process for product processing. Its composition is more complex and it is a multi-disciplinary, multi-variable process development. This systematic instrument is adapted to the characteristics of the vacuum application system itself. As a matter of fact, considering only technical requirements, it is possible to use a PC as a center to form a distributed measurement and control system for DCS (Distributed Computer System) computers; however, due to cost reasons, DCS systems can only be used in large-scale vacuum application systems. , such as high-energy physics, aerospace spatial simulation research, etc., and small and medium-sized vacuum application systems are rarely used (see Table 1). However, if the use of high-performance embedded microprocessor (MCU) as the core of the instrument, and MCU technology Combining the latest results of sensor technology and vacuum application technology, a process control instrument suitable for general small and medium-sized vacuum application systems was developed to provide a small-scale “DCS system†with high performance and cost ratio for the vacuum industry; It is conducive to the promotion and application of vacuum technology in more new fields. It also provides a quick and efficient technological transformation path for many small and medium-sized vacuum application systems in use, and can use shorter time and lower The cost will be replaced by automatic control and improve system efficiency. In addition, this kind of systematic instrumentation also has a comparative advantage. The communication function, it can not only complete the process control of some small and medium-sized vacuum application systems, but also can replace the grass-roots IPC in the DCS system, using more than one instrument and the upper PC to form a larger distributed measurement and control system. Such a system will be more economical and practical, and suitable for vacuum application system features.
Table 1 List of Classification of Automation Instruments in Domestic Vacuum Application System Table1 Classificationof vacuum applicationsystems Statistical Department Classification Statistics Pages Large-scale Instrument Combination System Bit+Single-smart Smart Instrument Combination System PLC (Programmable Logic Controller) System DCS (Computer Distributed) System Total Number of systems: 591,320,395 Percentage: 62.5%, 13.7%, 21.1%, 3.1%, 100% Table 1, data is based on statistics of vacuum and vacuum science and technology in the past three years (1998~2001).
2 Principles and Function Settings of the Instrument 21 Principle The vacuum application system is a complex multi-parameter dynamic system. The process of the vacuum application system is a comprehensive multi-parameter process. They are the process diagrams of vacuum smelting, VPD vacuum impregnation, and vacuum freeze-drying. In the figure, the law of the application parameters such as pressure (vacuum) temperature, humidity (water output), etc. at various points in the application system is shown as a curve, and if it is described by a parametric equation about time (t), It can be written as A(t)=Pi(t)+P2(t)+P(t)+Ti(t)+T2 t time, the system's parameter variable; t:0~ff process cycle design, from some The typical application system process flow curve sums up the relationship between various parameters, design vacuum application process program, adopts correct control algorithm (such as PIDFUZZY, etc.), and measures signal, equipment status signal, and various The alarm signal is processed comprehensively, and the required adjustment signal is output to each execution device so as to finally achieve the purpose of multi-parameter real-time control.
22 Function Setting The small and medium-sized vacuum application systems often have the characteristics of “small and fullâ€. Therefore, the instruments need to have more comprehensive functions and are summarized as follows.
Multi-channel, multi-sensor input functions, wide range of measurement, and high precision adjustment device and actuator diversity, requiring multiple, multi-channel control signal output, such as digital output, PWM signal Output, etc., and D/A output should also be considered when necessary.
There is a strong panel keyboard function, to be able to easily through the instrument panel keypad type, set the desired process display function: multiple physical quantities, multi-channel signal display or scroll, switch display, and work status lights and alarm Lamp display etc.
Communication function: to connect the printer and communicate with the host computer (PC), or to form a larger control system on line; consider the use of RS-232 interface, field bus interface program.
In control; there is a certain degree of uncertainty in the process, so. In the instrument's strong anti-interference ability g and real-time application / system operating state security features: the instrument should have a higher reliability and because of the diversity of vacuum application systems, so the instrument is equipped with a variety of more relays Array: The typical vacuum application i (craft) program or application model of the Dicardo Linden drive fcc2003Hblisl is fully monitored in a vacuum-free state. If an abnormal situation occurs, an alarm is issued and protection is automatically implemented.
3ZKY-50B intelligent vacuum system multi-parameter measurement and control instrument design points 3.1 MCU selection INTER MCU wide range of applications, product maturity, rich subroutine library, easy to develop; Although the chip is 8-bit processor, but it has 8-channel on-chip 10bit A/D conversion input port, the most suitable multi-channel input system; more I / O ports, easy to handle the switch input signal and output control signal; can directly output the PWM signal, so that the electric valve or other servo equipment adjustment Convenient; 16MHz, high processing speed, and with multiple interrupt sources, fC bus, power-down data protection, suitable for real-time control systems; 3.2 signal acquisition conditioning circuit vacuum sensor uses high accuracy, stability and linearity are better Thin film sensor (0. Bu 10 Pa) and piezoresistive vacuum sensor (10Pa ~ 100kPa), the instrument self-prepared precision constant current source (Ai 3.4 signal output and communication part of the different power multi-contact relay composition, to perform the switch control.
PWM output: used to drive the control stepper motor, electric control valve micro gas valve and other electromechanical servo device RS-232 communication interface: used to connect the printer, after expansion, can also use more than one type of instrument networking, and the host PC industrial computer DCS distributed measurement and control systems are formed on-line for use in larger vacuum application systems.
The requirements of the same vacuum application system can be achieved by modifying the vacuum application process program for some application systems with strong personalization. 3.5.3 Control algorithm for application system The control algorithm for the system is a subprogram structure with bit control algorithm and PID. The control algorithm FUZZY fuzzy control algorithm. Generally, the meter uses bit control and PID control algorithm. These two algorithms are simple and mature, and the accuracy of PID control algorithm can meet the general system. If the precision is high, fuzzy control FUZZY algorithm can also be selected. These configurations can be assembled through different algorithms. Subroutines to achieve 3.5.4 software security measures to take input digital filtering, software "watchdog" and other commonly used anti-jamming technology, in addition to the general vacuum system running slower, so the appropriate use of redundant design methods to further improve the system The stability of the 4ZKY-50B intelligent vacuum system multi-parameter measurement and control instrument applied in the vacuum freeze-drying system The schematic diagram of the food vacuum freeze-dried system with the ZKY-50B intelligent vacuum system multi-parameter measurement and control instrument as the control part has been stored There are many typical food freeze-drying process curves, so only need to select the curve type number and input processing weight according to the processing type; after confirming, it will automatically start running until the processing is completed, the user can also personalize settings through the keyboard. Select the corresponding vacuum vacuum temperature, humidity and other parameters at the key monitoring and control points , Make up the required process curve. After the setting is completed, some working data on the freeze-drying curve can also be determined, for example: pre-freezing rate temperature pre-freezing time, water vapor cooling time, sublimation rate and drying time, food eutectic point, etc. The instrument will automatically calculate these parameters. On the one hand, the data can be printed out through the interface for research purposes. On the one hand, it will also be used for automatic optimization and protection during system operation; for example, to prevent the heating temperature from exceeding the eutectic point in the sublimation phase. Destruction of freeze-dried food structure protection functions and other protective functions of instrument design.
5 Conclusion The integrated intelligentization and systematization of vacuum gauges (vacuum gauges) has become a trend of development. The process of developing the ZKY-50B multiparameter instrument shows that: after proper selection, an 8-bit MCU is used to realize the vacuum gauge system. It is already feasible to use a 1632-bit MCU with better performance. The instrument has a stronger function and a wider application range.
The systematization of vacuum measuring instruments has two meanings: one is that the instrument is used as a unit of the system (such as a smart sensor signal collector or a single loop measurement and control instrument in the system). The instrument is designed to be able to independently assume the automation center of the process control of small and medium-sized vacuum application systems, and can form a small DCS measurement and control system. This article is mainly concerned with the latter. This article is under the guidance of renowned vacuum expert Professor Liu Bingkun, and proposes valuable modifications. Opinions, express my heartfelt thanks
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