Pressure PID control loop
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There is a reactor pressure control loop, with a pressure control valve installed on the discharge line to regulate the reactor’s pressure. When the pressure becomes too high, the valve opens to release pressure. Under normal operating conditions, the pressure is around 80 Kpa; the PID control sets the SV value at 150 Kpa, the measured PV value is 80 Kpa, and the output MV value is 0. During start-up and shutdown procedures, the reactor is subjected to periodic pressure pulses, with these pulse pressures being around 90 Kpa. There is a significant discrepancy between this value and the set value of 150 Kpa when the loop operates in automatic mode. Logically, the control valve should not open at all, but in reality, once the pressure exceeds 90 Kpa slightly, the valve on the vent line opens. Since the pipes are relatively large, even a slight movement of the valve results in too low a pressure in the reactor. What is the cause of this, and how should it be addressed?
Switch to manual control or reduce the differential time
Please check whether differential action is enabled; if so, turn it off.
As PV changes, E(t) or ΔEn changes as well; due to the effect of the proportionality factor, MV changes as well. Therefore, switch to manual control, or set the proportionality factor as high as possible within the allowable range.
Manual control is normal, with a derivative of 0
During stamping, set it to manual full close and check to determine if there is a problem with the valve. Also, when switching to automatic punching mode, check whether the curve in the MV is indeed greater than 0%, or verify if the output signal has changed.
Without incorporating differential action, my understanding is that the goal of our control is to make the measured value as close as possible to the set value. However, no matter how we adjust things, it’s impossible for the measured value to equal the set value. When the measured value is 80 Kpa, the deviation is fixed; the controller then produces a steady-state output. When the measured value is 90 Kpa, the deviation decreases, and the controller’s output certainly changes compared to its steady-state output. My explanation of the process isn’t very convincing; let’s find the reason instead.
The value of proportionality was changed multiple times in experiments, but the results were not good
It works normally when operated manually; indeed, the MV curve during automatic stamping is greater than 0, and the output current does change. The channel was also changed – perhaps this phenomenon is normal?
Have you tried other control loops? If the situation is the same, then it’s a problem with the DCS regulator. (Functions such as pre-adjustment have been set up)
This post was last edited by jlshnlhj on 2018-5-10 at 16:00. \"The normal operating pressure is around 80 Kpa; the PID control SV setting is 150 Kpa, the measured value PV is 80 Kpa, and the output value MV is 0.\" This circuit is not functioning properly. Looking at the PID formula, whether it is the basic formula or the derivative-preceding formula, MV is related to the gain * error. As analyzed earlier: “As PV changes, E(t) or ΔEn changes as well; due to the proportionality factor, MV will change as well.” So switch to manual control, or set the proportionality as high as possible within the allowable range.