Valve PID

PID is a regulator parameter of the control loop, not a valve parameter.

What specific meaning does the size of P represent, and what does the size of D represent?

Please note that my last question is about the value of the P ratio, whose range is 1% to 300%. As for D, which represents differentiation, its range is from 0.1 to 10 points. What does the value of these parameters mean?

As seen before, an excerpt from that content: In practical engineering applications, the most widely used controller control laws are proportional, integral, and derivative control, commonly referred to as PID control, or PID regulation. The PID controller has been around for nearly 70 years; thanks to its simple structure, good stability, reliable operation, and ease of adjustment, it has become one of the key technologies in industrial control. When the structure and parameters of the controlled object cannot be fully understood, or an accurate mathematical model is not available, and other techniques from control theory cannot be applied, the structure and parameters of the system controller must be determined based on experience and on-site tuning; in such cases, PID control technology is the most convenient to use. That is, when we do not fully understand a system or the controlled object, or when it is not possible to obtain the system parameters through effective measurement methods, PID control technology is the most suitable approach. There is PID control, and in practice there are also PI and PD control. A PID controller controls the system by calculating the control amount using proportional, integral, and derivative actions based on the system’s error. Proportional (P) control: Proportional control is the simplest form of control. The output of its controller is proportional to the input error signal. When only proportional control is used, 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 it reaches steady state, then such a control system is said to have a steady-state error, or simply referred to as a system with steady-state error. To eliminate steady-state error, an “integral term” must be introduced into the controller. The integral term represents the time-dependent integration of the error, and as time increases, this integral term grows. In this way, even if the error is small, the integral term increases over time, which drives the output of the controller to increase and further reduces the steady-state error until it becomes zero. Therefore, a proportional-plus-integral (PI) controller enables the system to have no steady-state error after reaching stability. Differential (D) control: In differential control, the output of the controller is proportional to the derivative of the input error signal (i.e., the rate of change of the error). Automatic control systems may experience oscillations or even instability during the process of correcting errors. The reason is the presence of components with large inertia or components that introduce delay, which have the effect of suppressing errors; their changes always lag behind those of the errors. The solution is to make the change in the error-suppression effect \"proactive\", that is, when the error approaches zero, the error-suppression effect should be zero. In other words, it is often not sufficient to include only the \"proportional\" term in the controller; the role of this term is merely to amplify the magnitude of the error. What is needed now is the addition of a \"derivative\" term, which can predict the trend of error changes. Thus, a controller with both proportional and derivative terms can ensure that the control action to suppress the error becomes zero, or even negative, in advance, thereby preventing severe overshoot of the controlled variable. Therefore, for controlled objects with high inertia or lag, a proportional-plus-differential (PD) controller can improve the dynamic characteristics of the system during the regulation process. Parameter tuning of the PID controller is a core aspect of control system design. It determines the values of the proportional coefficient, integral time, and derivative time of the PID controller based on the characteristics of the process being controlled. There are many methods for tuning PID controller parameters, which can be broadly divided into two categories: one is the theoretical calculation tuning method. It mainly determines the controller parameters through theoretical calculations based on the mathematical model of the system. The calculation data obtained using this method may not be directly usable; it must still be adjusted and modified based on actual engineering conditions. The second is the engineering tuning method, which relies primarily on engineering experience, is carried out directly during the testing of control systems, and is simple and easy to master; it is widely used in practical engineering applications. The engineering tuning methods for PID controller parameters mainly include the critical ratio method, the response curve method, and the attenuation method. The three methods each have their own characteristics, and what they all have in common is that experiments are conducted first, followed by the tuning of controller parameters using engineering experience formulas. However, the controller parameters obtained using either method require final adjustment and refinement during actual operation. The critical ratio method is generally used nowadays. The steps for tuning the PID controller parameters using this method are as follows: (1) First, pre-select a sufficiently short sampling period for the system to operate ； (2) Only a proportional control element is added, until the system exhibits critical oscillation in its step response to the input; at that point, the proportional gain and the critical oscillation period are recorded ； (3) The parameters of the PID controller are calculated using formulas under a certain degree of control.