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    Home > Active Ingredient News > Drugs Articles > Application of Yudian instrument in constant pressure water supply

    Application of Yudian instrument in constant pressure water supply

    • Last Update: 2014-11-10
    • Source: Internet
    • Author: User
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    Chen Wei (Department of automation, Xiamen University, Xiamen 361005, Fujian) Abstract: This paper introduces a constant pressure water supply system with variable frequency and speed regulation, which is composed of AI Artificial Intelligence regulator and PLC, and expounds the realization scheme and circuit principle of the system Because of the self-learning fuzzy control algorithm of AI instrument, the system has the advantages of simple structure, stable operation and high performance index Key words: water supply; frequency conversion; AI intelligent regulator introduction: constant pressure water supply has been widely used in industrial and civil water supply systems Due to the uncertainty of the load change of the system, it is difficult to achieve the ideal effect by using the traditional PID algorithm to achieve the dynamic characteristic index of pressure control In the early design of the constant pressure water supply automation control system, many kinds of imported regulators were used, and the dynamic characteristic index of the system was always unstable Through the comparison of practical application, it was found that the control scheme formed by the application of fuzzy control theory had better effect in the constant pressure system In the process of implementation, ai-808 artificial intelligent regulator is selected as the main controller, combined with FX1N PLC logic control function, the full-automatic constant pressure water supply in the water plant is well realized For the pressure and logic control scheme realized by PLC alone, it is difficult to write a perfect fuzzy control algorithm due to the lack of PLC's calculation ability, and the adjustment of parameters is also more troublesome, so the scheme proposed has high cost performance Working principle: the system is mainly composed of ai-808 artificial intelligence regulator, frequency converter, control contactor group, water pump, valve, pressure transmitter, etc Due to the high power of the water pump, only one frequency converter is used to save the cost Two of the three water pumps can adopt the frequency converter to adjust the speed, so that one can be switched to another for frequency conversion control when one is in fault or maintenance Figure 1 is the schematic diagram of the water supply system The pressure sensor detects the pressure of the main outlet pipe, and sends it to the ai-808 instrument through the transmitter Compared with the set value, the pressure error and error change rate are obtained After the operation of the control algorithm combining the fuzzy and PID characteristic of ai-808, the output control signal (4 ~ 20mA) is sent to the control end of the inverter By adjusting the frequency, the outlet pipe pressure can reach the required index When the user and water volume increase, when the frequency conversion of one water pump reaches 50Hz, it still can't meet the water supply pressure requirements, PLC will detect the low pressure signal of ai-808 regulator, and add another water pump for power frequency operation according to its logic and process requirements; similarly, when the user's water consumption decreases, PLC will exit one power frequency water pump after receiving the high water pressure signal of ai-808 regulator When the system is running, the frequency converter is a method of fixed control of a certain water pump without switching multiple water pumps This can avoid the impact of frequent switching on the system and frequency converter, and has high reliability At the same time, considering the flexibility and maintenance, the system can select one of the two pumps to operate by frequency conversion manually, and can also reduce the loss caused by the long-term low-frequency operation of one pump Control algorithm The PID controller commonly used in the industrial process is suitable for the linear steady-state system, while the object of the water supply system often contains nonlinear and time-varying links, and some parameters are unknown and slowly changing, so it is difficult to achieve the ideal control effect by using PID control alone The AI Artificial Intelligence regulator adopts the dual-mode control algorithm combining fuzzy control and improved PID, as shown in Figure 2 When the control starts, the error e=Y-s is large, that is, when the deviation | e | ≥ EM (EM is the boundary value of the dual-mode control algorithm E), the system adopts the fuzzy control algorithm, which has good dynamic performance After the error is gradually reduced, i.e the deviation | e | quantifies and fuzzes the error E and the error change rate C, the fuzzy control rule with correction factor is adopted: P = [α e + (1 + α) C] where: P is the integer value of the control quantity u; α is the number between 0 and 1 Changing the value of α can change the fuzzy control rules of the dual-mode algorithm, thus changing the dynamic quality of the system AI regulator has the function of self-learning and self-adjusting in the regulation process The improved PID algorithm adopts anti integral saturation and incomplete differentiation In the formula, KD is the differential gain Under the step action, the ratio of the initial value of PD output to the final value of Zui In order to limit the effect of differential mutation, KD should not be too large, generally 5-10 During the debugging process, when the setting value changes, the control system adjusts as shown in Figure 3 When the load change is reflected through the regulating valve, the regulating process is shown in Figure 4 Equipment selection and function ai-808 artificial intelligence industrial regulator ai-808 artificial intelligence regulator has advanced control algorithm with Fuzzy Logic PID regulation and parameter self-tuning function When the error is large, the fuzzy method is used to adjust, so as to eliminate the phenomenon of PID saturation integral; when the error is reduced, the improved PID algorithm is used to adjust, and can automatically learn and memorize some features of the controlled object in the adjustment, so as to optimize the effect Zui It has the characteristics of no overshoot, high precision, simple parameter determination and good control effect for complex objects Its overall regulation effect is more obvious than the general PID algorithm This point has been verified in the system debugging At first, the simple PID regulator produced in Japan was selected In the process of water consumption change and water pump switching on and off, its overshoot and stability time are not ideal After using ai-808 intelligent instrument, its dynamic and static indexes meet the requirements FX1N series PLC is selected as PLC, and the output is relay type Because PLC only completes the logic functions such as automatic switch of water pump, so it does not need analog input and output module, thus saving investment The pressure closed-loop control of the system is completed by ai-808 artificial intelligence instrument, and the superiority of the algorithm is far higher than the simpler PID algorithm in PLC The frequency converter adopts Emerson td2000-4t2000p frequency converter, which is suitable for water pump load The frequency can be controlled by the current signal output from the manual potentiometer or ai-808 regulator The switching of the two modes is realized by the manual / automatic switch of the operation console The multi-function terminal of frequency converter is defined as potentiometer current signal control mode The design of the control console of the system takes into account two operation modes, manual and automatic In the manual state, each water pump and valve can be opened / stopped separately, and the frequency of frequency converter can be manually adjusted by multi turn potentiometer; in the automatic mode, the water pump to be put into operation is determined by the selection switch, so that when a water pump is maintained, it can be withdrawn from the automatic operation without affecting the normal operation of the system In addition to PLC and ai-808 regulators, the console is also equipped with water level indicator, branch pressure indicator and frequency meter Parameter setting ai-808 regulator provides a variety of user setting modes, so that it can achieve satisfactory control effect for different controls The parameter setting determines the static and dynamic performance of the system The parameter setting of the system is as follows: given value: 0.43 ~ 0.47mpa hial: upper limit alarm, no need Low: lower limit alarm, no need Dhal: positive deviation alarm, the system is used to control the switch of water pump, dhal = 0.05 dlal: negative deviation alarm, the system is used to control the switch of water pump, dlal = 0.05 DF: return difference (dead zone, hysteresis), which is used to avoid frequent adjustment due to the fluctuation of measured input value, and the position adjustment does not work within the return difference range, DF = 0.05 CTRL: control mode, ai artificial intelligence adjustment / PID adjustment, Ctrl = 1 M5: keep the parameters, which mainly determines the integral function in the regulation algorithm Similar to PID integral time, the smaller M5 is, the stronger the system integral function is When M5 = 0, the integral and AI Artificial Intelligence regulation are cancelled to become PD regulator, and the system value = 25 P: The rate parameter is directly proportional to the change of the measured value when the instrument output changes by 100% per second, P = 1000 / rising unit value of the measured value per second (the system is defined as a unit by 0.1), P = 5 T: The smaller the lag time is, the greater the proportion and the integral effect are, the weaker the differential effect is, but the stronger the overall feedback effect is; on the contrary, the larger the T is, the weaker the proportion and the integral effect are, and the stronger the differential effect is, t = 4 CTL: output cycle, reflecting the speed of instrument operation and regulation, CTL = 2 SN: input feedback signal type, Sn = 33, signal is 1-5V Conclusion: the system has been running for many years in the field, which adopts ai-808 artificial intelligence regulator and FX1N PLC (1) Using AI Artificial Intelligence regulator, using the control scheme of combination of fuzzy control and PID, the advantages of the two controllers are brought into play, achieving better dynamic and steady-state indexes, and the advantages of fast recovery time and small overshoot for system pressure regulation are achieved Its self-tuning function provides a convenient and quick parameter setting method for users, and the system stability error is within ± 0.01Mpa (2) The motor power is 180kW, and the single frequency conversion switching mode is conducive to reduce the system cost (3) The variable frequency speed control system makes the pump motor run under soft start, no impulse current, long service life and good energy saving effect.
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