A programmed temperature rise for heating

PID stands for Proportional, Integral, and Derivative

Concepts and basic principles of PID control (1) 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. 　　(2) 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 referred to as a system with steady-state error, or simply a system with 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; it drives the output of the controller to increase, thereby further reducing 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 steady state. 　　(3) 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 high 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 \"lead,\" that is, when the error approaches zero, the error-suppression effect should be zero. In other words, it is often insufficient to introduce only a \"proportional\" term in the controller; the function of this proportional term is merely to amplify the magnitude of the error. What is needed now is a \"derivative\" term, which can predict the trend of error changes. Thus, a controller with both proportional and derivative terms can bring the control action to eliminate the error to zero, or even to a negative value, 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 regulation. Parameter tuning of the PID controller Parameter tuning of the PID controller is a core aspect of control system design. It determines the values of the proportional gain, integral time, and derivative time of the PID controller based on the characteristics of the process under control. 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 and is carried out directly during the testing of control systems. It is a simple method that is easy to master, and 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.

It was explained in great detail, thank you :)

Hehe, it’s the same for me – when working on my graduation thesis, I also messed up the program-controlled temperature PID settings in the microreactor. Luckily, there was another one in the lab, so I used that one to get things sorted out. But it’s been a long time since graduation, and I’ve almost forgotten it. I remember that in the course on Instrumentation Automation, the PID parameters represented proportion, integration, and differentiation respectively. At that time, the values were p=2.5, d=2, and i=200; maybe that’s correct. I need to ask my colleagues in the lab as well. Personally, I think there is a certain relationship between the PID parameters and thermocouples – factors such as the length, thickness, and material of the thermocouples affect the temperature readings. PID is simply a set of rules for calculating these values, which are then used to adjust the temperature according to the set program. That’s roughly what I mean; if I’m misunderstanding something, please advise me

PID and programmed temperature rise are not the same concept. PID is a temperature control method that adjusts control parameters such as response speed based on the relationship between the set temperature value SP and the measured temperature value PV over time. A constant temperature can also be controlled using PID; there is also on-off control (which provides poor control performance and is prone to oscillations). Programmed temperature rise simply refers to the process curve by which the set value SP changes over time according to a predetermined program. Programmed temperature rise addresses the question of \"what\" should be done, while PID addresses the question of \"how\" it should be done This post was last edited by doing168 on 2009-4-8 22:24]

This post was last edited by zhousf on 2012-6-1 11:18. Donging168 explained it very clearly. Recently, I need to develop a program-controlled temperature control system for users. I used to think that program-controlled temperature control involved not only adjusting the set values according to pre-defined curves, but also taking into account issues such as the temperature control program automatically extending the waiting time when the predetermined time has passed yet the actual temperature has not reached the target value. After examining the products of various manufacturers, it became clear that in most cases, program-controlled temperature regulation simply involves changing the set values according to pre-defined curves. At the same time, I am also not very satisfied with such a plan.