A problem with the output of the PID regulator
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Happy New Year to everyone! I’ve recently encountered a problem that’s quite confusing, so I’m here to ask for advice! ! When calibrating the Shangrun WP-08 regulator (which has only PI control), it was found that with a set value of 0.3 MPa and an analog input pressure of 0.3 MPa, the regulator’s output current was 12 mA. When the analog input pressure increased to 0.4 MPa, the output current decreased sharply before gradually declining further due to the integral effect. When the analog input pressure was then reduced slowly from 0.4 MPa back to 0.3 MPa, it was observed that the regulator’s output stopped decreasing and instead started to increase. I don’t know what the reason is; how can this phenomenon be explained? The regulator should be fine; I’ve tried several other regulators and the same issue occurs with them.
This is normal; the regulator adjusts in advance based on the trend of changes in the input value. When the input value shows a downward trend, the regulator determines that the output will gradually increase. It’s not possible for it to wait until the input value reaches the set value before taking action. This is why PID control can achieve very precise regulation
The regulator output is normal, in line with the PI control law.
Take a look first; the setting parameters should include positive and negative effects. By reversing these parameters, you can achieve the desired result
Based on the described phenomenon, it seems to be a reactive regulator that gradually reduces the analog input pressure from 0.4 MPa toward 0.3 MPa, thereby reducing the deviation; as a result, the output increases. When it reaches 0.3 MPa, the regulator’s output current remains unchanged.
Thank you for your reply, but how should we analyze the calculations from the regulator output? I’ll share my analysis; please help correct me if there are any mistakes. Thanks! ! Start: The set value of the regulator is 0.3 MPa; a pressure of 0.3 MPa is applied to the regulator as an input. At this point, the output current of the regulator is 12 mA. Next, a pressure of 0.4 MPa is applied to the regulator (which corresponds to a step response). The resulting deviation is 0.4 – 0.3 = +0.1 MPa. Based on this deviation, it can be calculated that the output current of the regulator should decrease by 4 mA after 1 minute, meaning the output current should be 12 – 4 = 8 mA. Next: A pressure of 0.35 MPa is applied as input to the regulator; at this point, the deviation is 0.35 – 0.3 = +0.05 MPa. Based on this deviation, it can be calculated that the output current of the regulator should be reduced by 2 mA after 1 minute, meaning the regulator’s output current should be 8 – 2 = 6 mA. Therefore, when a pressure close to 0.3 MPa is applied as input to the regulator in simulation, the output current value of the regulator should continue to decrease, although the rate of decrease will become smaller. Please help point out any issues; thank you! !
But the deviation is still positive, so the output of the regulator should continue to decrease. Seeking advice!
Could you share some materials with me? I realize there are still many of my blind spots.
Proportional control: the regulator’s output is proportional to the input deviation； The characteristic of integral control is that as long as the deviation is not zero, a corresponding control signal will be generated, which in turn affects the controlled variable ； The function of differentiation is to control changes in deviation and prevent such deviations from developing; it exerts a controlling effect on any change in deviation, stopping those changes from occurring