Adjusts PID coefficients

Practical ways of adjusting the control loops (a short explanation of the coefficients)

This article describes my subjective opinion of the engineer.

Conclusions made from the explanations of Klaus Liebl (Klaus Liebl) and personal experience.

Before starting the adjustment of the PID controller, it is necessary to check in advance that there are three components for adjustment:

1. A convenient graph should be created that would allow monitoring changes in the process (preferably with a scaling function);

2. The PID function block must be installed in a place in the program that guarantees its cyclic call with equal timings (time intervals).

Example: OB100 or periodic task with a cycle of 100 ms;

3. It is important to understand which formula is used in the library. I know 2 formulas:

 

Формула ПИД-коэффициентов

In this formula, the integration coefficient is very important, which can be either direct or inversely proportional.

The Ziegler-Nickels method is good, but it has the disadvantage that in complex interconnected systems, when it is impossible to exclude an external effect on the process, setting up a specific circuit can take a very long time.

I will discuss in more detail the main coefficients.

1. The proportional coefficient "P" (gain) is the main factor of the regulator. The speed and direction of operation of the regulator depend on it. The main task of the PID controller is to stabilize the process variable at the set value (setpoint or setpoint). Stabilization and swinging are two different things.

If the "P" parameter is negative, the contour will start to work in the exact opposite way, and, therefore, we exercise with it the accuracy and set the value to 0.5.

So, for example, if the circuit heats up any medium, then "P" must be positive, but if you cool something, then the "P" -code should be negative.

2. The integral coefficient "I" influences the regulatory process. His role is "accuracy". It is worth paying attention to the formula 1.

If it is not inversely proportional, then to increase the integral component it will be necessary to decrease this coefficient, in our case, to increase it. "Accuracy" indicates how large the slope of the curve of the process variable graph should be.

If you need to reassure periodic fluctuations, it is sufficient simply to greatly increase the integration factor (for example, from 0.5 to 8.0).

3. Differential coefficient "D" serves to calming complex mutually inert systems, for fast interrelated processes, when the impact on the object causes wave-like damped processes, similar to those when we throw a stone into the water and see divergent waves. With each wave, the oscillations noticeably subside. To level these oscillations, this coefficient serves as well.

Attention: for slow processes - more than 40 seconds from the minimum to the maximum of the curve curve - this parameter should be excluded, that is equal to 0.

Useful video:
PID_simple

#Adjusts, #PID, #coefficients, #setting, #tuning, #controller, #simple

Russian version



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