Abstract: This paper analyzes the theoretical basis of the application of adaptive PID control in the gas industry, and expounds the successful application of the PID regulator of Yudian Instrument in the automatic ratio system of hydrogen and nitrogen, focusing on the working process and operation method of PID regulator. Keywords: hydrogen-nitrogen automatic ratio intelligent industrial regulator self-tuning PID control preface With the rapid development of modern industry, gas equipment is gradually applied to the chemical, electronics, steel and other industries; the traditional manual gas distribution device has not reached the follow-up With the technical indicators of purity, flow and pressure of gas, the flexibility is obviously not up to the requirements of gas consumption. Automatic proportioning devices have emerged. However, the current control methods used in the gas industry are also traditional fuzzy control methods. Currently, most industrial regulators on the market cannot meet the accuracy requirements in gas distribution systems. The application of Yudian's AI artificial intelligence industrial regulator in the automatic hydrogen ratio system is a rare success story realized by the automatic control of the gas industry. The input of AI artificial intelligence industrial regulator adopts digital correction system, built-in common thermocouple and thermal resistance non-linear correction table, the measurement accuracy is up to 0.2 level; adopts advanced modular structure to provide rich output specifications; the key is to adopt advanced Self-tuning PID algorithm. The theory of self-tuning PID control is based on various forms of PID control algorithms used in most industrial control loops. PID is the abbreviation of Proportion, Intergral and Differential. The control law of PID means that the output signal of the controller is a function of the digital relationship of the input deviation proportional, integral and differential. The control law of PID is as follows: u(k)=kp[e(k)++TD] where kp is the proportional coefficient; T1 is the integral time constant; TD is the differential time constant; u(k) is the sampling time k The output value of the time; e(k) is the deviation value of the sample k; e(k-1) is the deviation value at the sampling time k-1. PID regulation is a combination of proportional adjustment, integral adjustment and differential adjustment. Its proportional action can make the deviation corrected quickly; the integral action can finally eliminate the residual, and the differential action can occur immediately when there is deviation. The effect of the correction deviation of the amplitude is generated, thereby shortening the adjustment time and improving the adjustment efficiency and accuracy. Although the accuracy of the conventional PID adjustment has been significantly improved compared with the manual adjustment and the position adjustment, the fluctuation has been greatly reduced, but the ordinary PID control is not suitable for the control object with large time lag and the control object with large parameter variation. The self-tuning PID control method is developed on the basis of the ordinary PID control method. It selects the P, I, and D values ​​according to the lag time and the deviation size and effectively uses the PI, PD or PID control. This method is effectively shortened. Lag time and improved accuracy. Working process and operation process of AI type regulator in application (1) Hydrogen and nitrogen automatic proportioning system overview The structure of hydrogen and nitrogen automatic proportioning system consists of N2 pipeline, 3H2+N2 pipeline, mixing tank, globe valve, flowmeter, pressure gauge, It consists of an analyzer, an electric valve, a PID regulator and an electronic control system. The system process flow chart is shown in Figure 1. Figure 1 N2, 3H2+N2 enters the mixing tank and is sampled by the outlet. The sensor sample shows the purity and converts the purity sampling analog quantity into 4-20mA current. The analog quantity is transmitted to the PID regulator through the PID regulator. After the microprocessor analyzes and processes, the 4-20 mA current is transmitted to the electric regulating valve to control the electric regulating valve to control the flow rate of 3H2+N2, thereby controlling the mixing ratio of the hydrogen in the mixed gas. The electrical schematic of the automatic control electrical system is shown in Figure 2. Figure 2 The above analysis shows that the automatic control principle diagram of the hydrogen-nitrogen automatic ratio system is shown in Figure 3. Figure 3 (2) PID regulator self-tuning process example analysis Huada Microelectronics Co., Ltd. hydrogen and nitrogen automatic ratio system requires purity of 15%, according to the recorded data, the process of self-tuning control changes as shown in Figure 4. Figure 4 PID setting value is 15%, deviation is expressed by E, β = 1-2%, ε = 0.2%; When the purity is below a, that is, E < -1, the valve is fully open, no PID is required. Control; When the purity is between ab, ie -1<E<-0.2, it is controlled by PD, because in the general PID control, when the valve has a large change, due to the large deviation at this time, The valve has mechanical inertia and the hydrogen analyzer has sampling hysteresis, so under the action of the integral term, it tends to produce large overshoot and long-term fluctuation; when the purity changes between bc, ie |E|<0.2, PID adjustment Control; when the purity is between ce, the valve opening is reduced; when the purity is between ef, it returns to the PID adjustment control; when the purity is between fg, it returns to the PD adjustment control. After three tuning cycles, the purity will stabilize at 15 ± 0.2%. According to the actual debugging record, the AI-type PID regulator can fully meet the system control accuracy control requirements. (3) Performance superiority of AI type PID regulator AI type PID regulator is compatible with input of thermocouple, thermal resistance, linear voltage, linear current and linear resistance; wide measurement range, high precision, small temperature drift, short response time; output Specifications include relay contact switch output, thyristor contactless switch output, SSR voltage output, thyristor trigger output, and linear current output. The instrument hardware uses an advanced modular design with five functional module sockets: Auxiliary Input (MIO), Main Output (OUTP), Alarm (ALM), Auxiliary Output (AUX), and Communication (COMM) modules. In the automatic hydrogen ratio system, we selected the AI-808 function-enhanced artificial intelligence industrial regulator, because it adds manual/automatic bumpless switching and valve motor control on the basis of AI-708. Select to install I4 auxiliary input module, can expand 0-20mA or 4-20mA current signal input, and built-in 24VDC power output, can be directly connected to 2-wire transmitter; output selects optically isolated linear current output module, supports 0-20mA And 4-20mA output, occupying the internal 12VDC power supply of the instrument. If you need an alarm system, you can also choose one alarm or two alarm modules. (4) AI type PID regulator parameter setting and operation method in system application AI type PID regulator has rich parameters to define the input, output, alarm, communication and control mode of the instrument. The input parameters related to the normal use of the system must be set in advance, the input specification SN is set to 15 (4-20mA input); the output specification OPT is set to 4 (4-20mA linear current output); the control mode is set to 1, using PID adjustment Allows you to perform auto-tuning from the panel. The hydrogen-nitrogen automatic proportioning equipment is installed and the power supply is started after the continuous condition is met. Firstly, the valve opening degree is manually adjusted by the regulator to achieve the purity of the required gas distribution, and the regulator setting value is a required value (for example, 15%), and the like. After the stabilization, the auto-tuning function is started from the regulator panel. The display window flashes the AT word and enters the auto-tuning function. The PV display window will show the purity value fluctuation, because the instrument performs the position adjustment at this time, the internal microprocessor of the instrument is based on the position. The control generates vibration, analyzes its period, amplitude and waveform to automatically calculate the control parameters such as M5, P, t, etc. After 2-3 oscillations (about 20-30 minutes), the display stops flashing "AT", self-tuning End. At this point, the system is already in normal working condition. If the purity is fluctuating, the M5, P, and t parameters can be manually adjusted. M5 is the hold parameter, which has the same effect as the integration time of PID adjustment. The smaller the value, the stronger the system integral action; the larger the value, the shorter the integration time; P is the rate parameter, similar to the proportional band of PID adjustment, but The opposite is the change. The larger the P value is, the proportional and differential effects are proportionally enhanced. The smaller the P value is, the smaller the proportional and differential effects are. The t is the lag time. The hysteresis effect of the controlled system is the main reason affecting the control effect. The system lag time The larger, the more difficult it is to achieve the desired control effect. As long as the hydrogen analyzer and the electric valve with high precision and fast response are selected, the system works well. In conclusion, using the AI ​​type regulator to control the hydrogen-nitrogen automatic ratio system is much better than manual, position adjustment and general adjustment. The AI ​​type artificial intelligence adjustment algorithm is a new type of algorithm that uses fuzzy rules for PID adjustment. It can automatically learn some of the characteristics of the memory controlled object in the adjustment to make the effect more optimized intelligent industrial regulator. Http://news.chinawj.com.cn
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