pressure control issues

Reply to 1# Jingjing Zhiyuan adopts the empirical trial method, artificially adding step interference to observe the transition process curve, and changing the corresponding parameter setting values ​​according to the impact of PB, TI, and TD on the transition process, first PB, then TI, TD, and repeat the test many times until the empirical data is satisfied.: PB 30-70% TI 0.4-3min

In engineering practice, the most widely used regulator control rules are proportional, integral, and differential control, referred to as PID control, also known as PID regulation. PID controller has been around for nearly 70 years. It has become one of the main technologies of industrial control because of its simple structure, good stability, reliable operation and convenient adjustment. When the structure and parameters of the controlled object cannot be fully grasped, or an accurate mathematical model cannot be obtained, and other technologies of control theory are difficult to adopt, the structure and parameters of the system controller must be determined by experience and on-site debugging. At this time, it is most convenient to apply PID control technology. That is, when we do not fully understand a system and the controlled object, or cannot obtain system parameters through effective measurement methods, PID control technology is most suitable. PID control, in practice there are also PI and PD control. The PID controller uses proportion, integral, and differential to calculate the control amount based on the system error. 　 Proportional (P) control Proportional control is the simplest control method. The output of its controller is proportional to the input error signal. When there is only proportional control, there is a steady-state error in the system output. 　 Integral (I) control In integral control, the output of the controller is proportional to the integral of the input error signal. For an automatic control system, if there is a steady-state error after entering the steady state, the control system is said to have a steady-state error or simply a system with a difference (System with Steady-state Error). In order to eliminate the steady-state error, an "integral term" must be introduced in the controller. The integral term of the error depends on the integration of time. As time increases, the integral term will increase. In this way, even if the error is small, the integral term will increase as time increases, which promotes the controller's output to increase and further reduce the steady-state error until it is equal to zero. Therefore, the proportional + integral (PI) controller can make the system free of steady-state errors after entering the steady state. 　 Differential (D) control In differential control, the output of the controller is proportional to the differential of the input error signal (ie, the rate of change of the error). Automatic control systems may oscillate or even become unstable during the adjustment process to overcome errors. The reason is that there are large inertia components (links) or delay components, which have the effect of suppressing errors, and their changes always lag behind the changes in errors. The solution is to make the change in the effect of suppressing errors "ahead", that is, when the error is close to zero, the effect of suppressing errors should be zero. That is to say, it is often not enough to only introduce the "proportional" term in the controller. The role of the proportional term is only to amplify the amplitude of the error. What needs to be added now is the "differential term", which can predict the trend of error changes. In this way, a controller with proportion + differential can make the control effect of suppressing the error equal to zero or even negative in advance, thus avoiding serious overshoot of the controlled variable. Therefore, for controlled objects with large inertia or hysteresis, the proportional + derivative (PD) controller can improve the dynamic characteristics of the system during the adjustment process. I work in fine chemicals and don't know much about the petrochemical industry, so I can only provide some peripheral reference. This is a common formula: Find the best parameter setting, check in order from small to large, first proportion, then integral, and finally add differential. The curve oscillates frequently, the proportion dial needs to be enlarged, the curve floats around the big bay, turn the proportion dial small, the curve deviation is slow to recover, the integration time goes down, the curve fluctuation period is long, the integration time is longer, the curve oscillation frequency is fast, lower the differential first, the dynamic difference is large, the fluctuation is slow, the differential time should be lengthened, the ideal curve has two waves, the front is high and the back is low 4 to 1. Once you look at the second adjustment and analyze it more, the adjustment quality will not be low.