With the development of fieldbus technology, traditional analog instruments gradually give way to intelligent digital instruments and have digital communication functions. According to the development of fieldbus intelligent instrument technology, a zirconia intelligent oxygen analyzer based on fieldbus is designed. Its temperature control system adopts the expert PID control principle to improve the heating speed and accuracy. introduction With the development of fieldbus technology, traditional analog instruments gradually give way to intelligent digital instruments and have digital communication functions. According to the development of fieldbus intelligent instrument technology, a zirconia intelligent oxygen analyzer based on fieldbus is designed. Its temperature control system adopts the expert PID control principle to improve the heating speed and accuracy. 1. Structure of bus intelligent oxygen analyzer The intelligent oxygen analyzer based on the CAN bus uses the single-chip microcomputer C8051F040 as the central controller. The peripheral circuits and interface circuits of the system expansion are small, the reliability and stability of the system are high, and the system function expansion and software and hardware upgrade are more convenient. The hardware structure of the system is shown in Figure 1. The peripheral hardware circuit mainly includes six parts: system calibration, data acquisition, temperature control, calendar clock, liquid crystal display with touch screen, and CAN bus interface. Figure 1 System hardware structure The liquid crystal display with touch screen provides a powerful human-machine interface, and related signals and adjustable parameters can be displayed and modified on it. The system uses a regulated power supply, which has the advantages of large power supply voltage range and strong anti-interference ability. The host is a kind of intelligent instrument based on single chip microcomputer. All calculation, processing and control are completed by software. Modular components are used for the conversion of oxygen potential and temperature signal input and current output. These components have the characteristics of high reliability and high precision. Due to the high integration of the components used, the structure of the whole machine is simple, the reliability is improved, and the use, maintenance and repair are convenient. The oxygen potential and temperature signals are converted into 0-5V signals by their respective processing modules, and then converted into digital quantities by multiple switches and A / I), and the single-chip computer calculates the oxygen quantity according to the "Nernst" formula. The system is equipped with a PID temperature adjustment function, and the heating furnace is controlled by a solid-state relay. The system is also equipped with configuration switches, which can make the instrument work in different ways. 2. Hardware design of temperature control system Cygnal New edition of "List of Chinese Instrument and Meter Manufacturers" The 51 series MCU C8051F040 is a mixed-signal system-level MCU integrated on a chip. In one chip, it integrates the analog and digital peripherals and other functional components required by an intelligent node that constitutes a single-chip data acquisition or control. The current development direction of 8-bit microcontroller control system. The chip has one 12-bit and one 8-bit multi-channel ADC, two 12-bit DACs, two voltage comparators, one voltage reference, one 32kB FLASH memory, and high-speed fully compatible with MCS-51 instruction set CIP-51 core, the peak speed can reach 25MIPS, and there is a hardware-implemented UART serial interface and a CAN controller that fully supports CAN2.0A and CAN2.0B. Pins 18 and 19 of C8051F040 are the AIN0.0 and AIN0.1 pins, respectively. Because the C8051F040 has an ADC module on-chip, the temperature signal can be directly input to the AIN0.0 and AIN0.1 pins after peripheral filtering and amplifying circuits, AMUX The working mode selects single-ended input mode. Select thermocouple as the temperature sensor. After the signal is amplified, the voltage is sent to the A / D terminal of C8051F040. After conversion, it is compared with the given temperature value. According to the PID adjustment algorithm and pulse width adjustment method, the value at this moment is calculated. After photoelectric isolation and power amplification, the heating power is controlled by controlling the on-off time of the high-power AC solid-state relay (zero-crossing type) to achieve the purpose of temperature control. The cold junction temperature measuring element adopts the integrated temperature sensor AD590, the measured temperature is detected by the AD590 temperature sensor, and is directly sent to the AIN0.1 input port of the single-chip microcomputer C8051F040 after voltage amplification. 3. Software design of temperature control system 3.1 Analysis of temperature control process The minimum period of heating on and off is 10ms, the shortest heating pulse length is 10ms, and the PID control output is the number of heating pulses. The greater the error, the greater the heating pulse value; the smaller the error, the smaller the heating pulse number. In order to make the PID output have a certain adjustable range, the sampling period, too small will make the range of the control amount is very narrow; but it can not be too large, otherwise it will reduce the control accuracy. Considering various considerations and experimental tests, the sampling period is set at 2s. In this way, the maximum pulse output (in a control period) of PID is 200. The heating process of the system is divided into three parts: first, when the temperature is in the initial stage or when the temperature difference is large, full power heating is used to quickly heat the heating element; second, when the temperature changes drastically, the output is turned off to let the temperature play an inertial role The next transition to the next stage. Because the heating element lags seriously, when the temperature rises too fast, it will cause the next stage of control failure or severe overshoot; third, when the temperature deviation and temperature change are within a certain range, adjust the PID parameters online according to expert intelligence to achieve fast and accurate control. 3.2 The principle of expert PID controller The temperature control system has the characteristics of non-linearity, strong coupling, time-varying, and time-delay. It is difficult to take into account the dual requirements of high accuracy and rapidity with conventional PID control. This paper proposes a compound control method that combines expert intelligence and PID, and fully applies expert experience and PID control quantitative adjustment characteristics to the control process. The bus intelligent oxygen analyzer requires the system temperature control range to be 680 ～ 760 ℃, and the temperature fluctuation after stabilization should not exceed 1 ℃. In order to achieve fast and accurate temperature control, the expert system PID control mode is established according to the characteristics of the controlled object, as shown in Figure 2. Figure 2 Functional block diagram of expert intelligent PID composite controller The inference structure of this expert controller adopts data-driven forward inference strategy. The production rule takes the form of IFe (n) ANDe (n) TNout (n). The key of the expert system is the establishment and determination of expert knowledge. Knowledge acquisition, some from the long-term summary of the process personnel, some with the help of knowledge and analysis in the field of control. Combining the expert system and the PID controller, using the expert system knowledge base to output and modify PID parameters, and changing the PID control method to achieve the best PID control effect. According to the object characteristics and design requirements, 99 control rules are designed, and the adjustment methods and adjustment parameters under the rules are stored in the controller in advance. The expert control rule determines the control method and whether the proportional coefficient KP, integral gain KI, and differential gain KD need to be modified according to the current deviation e (n) and the rate of change △ e (n). During the control process, the controller does not need to adjust the PID parameters according to the system identification results or a certain target function, but adjusts the basic PID parameters according to the current state: Kj = aTjKOj, J = P, I, D In the formula, KP, KI and KD are the basic proportional, improved integral and differential gains respectively; aTP, aTI and aTD are the proportional, integral and differential correction coefficients in the current adjustment state respectively. 3.3 Software flow The system software adopts C51 language and compiles and connects in the SiliconLaboratories integrated development environment. The temperature range of the instrument is 0 ～ 1000 ℃, the temperature control is 700 ℃ ± 1 ℃, the temperature control set value is 680 ～ 760 ℃, and it is continuously adjustable. When the temperature is greater than 800 ℃, the coupler protection function is activated. Data collection uses the method of averaging multiple measurements to avoid measurement errors. 4 Conclusion The fieldbus intelligent zirconia oxygen analyzer designed in this paper has the advantages of high automation level and simple structure. It plays a significant role in improving the production efficiency of thermal equipment such as power station boilers and coal coke ovens. Tests show that the temperature control system has the advantages of wide measurement range, high operating temperature, reliable operation, timely and accurate measurement, etc. At the same time, it overcomes the shortcomings of previous instruments such as instability and easy damage. The method is modified appropriately and can also be applied to other temperature control systems. Camping Mess Kit,Camp Pot,Camping Cookware,Outdoor Cookware Xianke Metal Products Factory , https://www.stainlessbarware.com
