Understanding the mnemonic for PID tuning
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The curve drifts around large bends; turn the scale knob in a smaller direction. The curve takes longer to return to its original position, so reduce the integration time. How should we understand the phrases “the curve drifts around large bends” and “the curve takes longer to return to its original position”? These two phrases seem to be contradictory
"\"The curve floats around the set point\" refers to the situation in a control system where the output curve fluctuates significantly near the set value and fails to stabilize quickly. At this point, the proportional gain should be reduced to make the system response more stable. "\"Slow recovery from curve deviation\" refers to the slow speed at which the control system tracks the set value or corrects deviations, and it is necessary to increase its response speed. At this point, the integration time should be reduced and the integration effect increased to help the system eliminate the deviation more quickly. These two sentences are not contradictory; they describe respectively the adjustment strategies that the control system should adopt in different situations. .
The former can be understood as amplitude, while the latter can be understood as period :)
These two statements are not contradictory; the former relates to the setting of the proportional gain, while the latter relates to the setting of the integral time. The curve moves in large bends, indicating that when the scale factor is too high, the transition time becomes prolonged, resulting in slow changes in the parameter being regulated. In other words, the curve of this parameter deviates significantly from the desired value over an extended period of time; during this time, the curve exhibits large fluctuations and irregular changes, following a path that resembles large bends. Then the proportionality should be reduced to minimize the residual error. The slow recovery of the curve from deviation means that when the integration time is too long, the curve returns to the given value slowly and non-periodically; therefore, the integration time should be reduced.