1 system design 1.1 hardware structure Graphite furnace power supply automatic control system hardware is based on 8031 ​​single-chip microcomputer, by extending the corresponding peripheral interface circuit and drive circuit. Its control system circuit box refers to 1.
Control order received date 2000407; revised date 200088 serial communication circuit open output output circuit analog 1 input circuit control unit consists of 1 gamma 18 1 single-chip program memory database storage, etc.; keyboard display and state refers to the circuit for input Control command program, display graphite furnace temperature and control parameters and refers to the operating state of the graphite furnace power supply; the switch input and output circuit is used to input the operating status information of the graphite furnace power supply, monitor each input variable and the connection with the autosampler or the atomic absorption host Signal, output control signal for graphite furnace power supply and other related equipment; analog input circuit is used to sample the temperature signal of the graphite furnace power supply, and output control signal for the temperature of the graphite furnace power supply after being processed by the control algorithm; serial communication circuit It is used for communication between the graphite furnace power supply and the general-purpose microcomputer, and the operation of the graphite furnace power supply is directly controlled by the microcomputer.
1.2 Software design According to the characteristics of the graphite furnace power supply and its requirements for the furnace temperature control performance indicators, we use fuzzy! 10 composite control technology automatically controls the temperature of the graphite furnace. Excellent dynamic performance and steady state control accuracy are achieved. The software design idea is that when the controlled variable deviation is greater than a certain threshold, the fixed value control mode is adopted to improve the response speed of the system and speed up the response process; when the deviation is reduced to the threshold, the switch is transferred to the fuzzy control mode to improve the system. Damping performance reduces overshoot during response. This combines the advantages of fixed control and fuzzy control. By the processing. The domain of fuzzy control is only part of the whole control theory domain, that is, the fuzzy control domain has been compressed, and the linguistic value equivalent to the linguistic variable, that is, the number of bins is increased, thereby improving the sensitivity and control precision of the system. When the deviation enters the steady-state equilibrium region of the fuzzy control, because the 10 control has an ideal adjustment effect in a small range near the equilibrium point, and its integral action can finally eliminate the steady-state error of the system, the system switches to and enters, 1 Control mode, control system box 2 intelligent switch design, where 41 system deviation threshold 7 is the corresponding value when the fuzzy controller error language variable takes zero value.
The controller outputs the output of the current time of the controller as the output of the controller before the output of the controller is the increment of the current time of the controller relative to the previous time. Since the output of the controller is always constrained during the actual control process, the output of the controller in the actual control process can be described as: 滓 滓 leakage, 篦 滓酹 滓酹 滓酹 胧蔌 胧蔌 胧蔌 胧蔌 åŠ åŠ åŠ åŠ åŠ åŠThe design of the 3 parameter self-tuning fuzzy controller is selected in the experiment. In the automatic control system of the graphite furnace power supply, the parameter self-tuning fuzzy controller with 2-level structure is adopted, 3. The lower-level algorithm realizes the fuzzy control function, and the upper-level algorithm realizes the fuzzy control. The tuning function of the parameters.
The parameter and the setting should be such that the steady-state error of the system is less than a fraction greater than zero, then the parameters of the controller must be adjusted according to the following formula. 2. The performance index of the system does not require the change of the steady-state error. After the system enters a steady state, the change in steady-state error tends to zero. Under certain conditions, the dynamic response rate of the system is affected. In order to make the system have an ideal dynamic response, it must be coordinated with the illusion. The fuzzy drawing rule for our design is called 1=1.525 heart.
Parameter tuning We can design a set of rules for the parameters of the women described by the language rules. That is, IfE 1.2, m1=2, p. where sigmoid is the linguistic variable of the error and error of the controlled variable, and 5; the linguistic value on its corresponding domain is 8, 殪, 5, 0, 5 , 18, etc., is the proportional 3 syllabic change, 1 is its corresponding domain according to the design of the fuzzy control rules and parameter tuning rules, the application of approximate reasoning synthesis algorithm, the computer offline calculation of fuzzy control and parameter tuning query, and This control and parameter tuning query is stored in the computer. Whenever the error of the sampling and the error of the sampling are separately quantified, the corresponding control quantity 7 and the setting parameter can be respectively found from the control and parameter setting query, so that the real-time computer real-time control can be conveniently realized for the industrial object. . The acquisition of control is the main feature of fuzzy control. A query that can be used for industrial process control must be obtained through rigorous practice testing and repeated modification.
4 Parameter Tuning 1 The control controller is a kind of 辄 integral differential controller, which is the most widely used controller. The mathematical model of the controller can be used as follows: the output of the controller; the input to the controller, which is the deviation signal of the given value and the output value of the controlled object, which is called the ratio of the controller respectively. Subdivision system. In the control system with the microprocessor as the hardware core, since the input and output states are sampled in real time by the sampling period, it is a discrete time control system. In discrete control systems, the controller uses a difference equation. Therefore, there is an output in which the illusion is the sampling time, the illusion is the deviation of the sampling time, and 7 is the sampling period.
In order to avoid the screwing (1), the deviation summation operation is followed by the increasing formula (1) stomach ie illusion = iiUc1 + A, Jj1lJ for a specific controlled object, the proportional system can be changed under the action of pure proportional control 7 which produces a critical oscillation, and according to 268 soil, 18 conditions, there are 31770.577 using the above formula, the parameter optimization algorithm can be applied to realize the self-tuning of the parameters.
2 Experimental research results The application of the light-controlled graphite furnace power supply industry, 4, the United States, the company produced 600,714100, 156701 produced by Nishimzu company for on-line analysis and testing, the test results, the price of the following element wavelength characteristics are as follows 918 heating steps, each step can be set temperature and temperature control mode, furnace temperature control range from room temperature 3000, heating rate 20003, temperature control accuracy 1 is actually less than inferior, temperature control reproducibility error, 3 external description After the hatred water and feedback loop, the ship's function is reduced, and the furnace temperature correction function.
Due to the adoption of infrared temperature measurement technology and fuzzy control technology, the temperature control level of the graphite furnace has reached a new level, and the furnace temperature is not affected by the voltage fluctuation of the grid, and is not affected by the change of the resistance of the graphite tube, and the atomization of the ashing temperature is solved. The temperature of the question is advanced. Filled in the empty power of the light control ink furnace in 1. The mountain is put on the market.
Li Hua. , 0351 series single-chip practical interface technology Beijing Beijing Aerospace University Press, 1993.
Zhu Liangzhu. Analytical instrument manual elbow. Beijing Chemical Industry Press, 1997.
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