Applications of PID Controller AI-808

Abstract: This paper analyzes the theoretical basis of the application of adaptive PID control in the gas industry, and expounds the successful application of Yudian PID controller in the automatic ratio system of hydrogen and nitrogen, focusing on the working process and operation method of PID controllers.

Key words: automatic ratio of hydrogen and nitrogen, intelligent industrial controllers, self-tuning PID contro

Foreword: 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 can not reach the requirements of. flow and pressure of subsequent gas use, and the flexibility is not enough for gas using. Automatic proportioning devices have emerged. However, the current control methods used in the gas industry are also traditional fuzzy control. Currently, most industrial controllers on the market cannot meet the accurate requirements in gas distribution systems. The application of Yudian industrial controller in the automatic hydrogen ratio system is a rare success story in the automatic control of the gas industry. The input of AI  controller adopts digital correction system, built-in common thermocouple and thermal resistance non-linear correction table, measuring accuracy up to 0.2 level; adopts advanced modular structure and provides rich output specifications; the key is advanced Self-tuning PID algorithm.

Theoretical basis for adopting self-tuning PID control method

Various forms of PID control algorithms are employed in most of current 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 numerical 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 proportionality factor; T1 is the integral time constant; TD is the differential time constant; u(k) is the output value at the sampling instant k; e(k) is the bias value of the sample k; e(k-1) is the sample The deviation value at 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 common 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 and operation process of AI controllers

(1) Overview of hydrogen-nitrogen automatic rationing system

The structure of the hydrogen-nitrogen automatic ratio system consists of N2 pipeline, 3H2+N2 pipeline, mixing tank, shut-off valve, flow meter, pressure gauge, analyzer, electric valve, PID regulator and electronic control system.

N2, 3H2+N2 enters the mixing tank and is sampled from the outlet. The sample is sampled by the hydrogen analyzer to show the purity and the purity sampling analog quantity is converted into 4-20mA current. The analog quantity is transmitted to the PID regulator, and the micro-processing is performed by the PID regulator. After the analysis and processing, 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.

(2) Analysis of PID regulator self-tuning

The hydrogen-nitrogen automatic rationing system of Huada Microelectronics Co., Ltd. requires a purity of 15%.

The PID setting value is 15%, and the 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, and PID control is not required;

When the purity is between ab, that is, -1<E<-0.2, it is controlled by PD. This is because in the general PID control, when the valve has a large change, the deviation is large at this time, and the valve has Mechanical inertia and hydrogen analyzers have sampling hysteresis, so under the action of integral terms, large overshoots and long-term fluctuations tend to occur;

When the purity changes between bc, ie |E|<0.2, the PID adjustment control is used;

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, return to PD regulation control.

After three tuning cycles, the purity will stabilize at 15±0.2%. According to the actual debugging records, the AI-type PID regulator can fully meet the system control accuracy control requirements.

(3) Performance superiority of AI PID controller

The AI type PID controller is compatible with thermocouple, RTD, linear voltage, linear current and linear resistance input; wide measuring range, high precision, small temperature drift, short response time; output specifications include relay contact switch output, SCR 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 to the 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.

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(4) Parameter setting and operation method of AI type PID regulator in system application

The AI type PID controller has a wealth of parameters to define the instrument's input, output, alarm, communication and control methods. 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 start the auto-tuning function 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 that affects the control effect. The system lag time The bigger the problem, 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.

Conclusion

The use of AI-type controllers used in the hydrogen-nitrogen automatic ratio system is much better than manual, position or general adjustment. The AI type artificial intelligence adjustment algorithm is a new type that uses fuzzy rules for PID adjustment. It can automatically learn some of the features of the memory be controlled in the adjustment to make the effect more optimized.