Step control

Does this mean that for the PIC4021, an MV value (OP value) of 0-30% corresponds to an opening degree of valve A of 100%-0% (the process of the valve closing), while an MV value (OP value) of 70-100% corresponds to an opening degree of valve A of 0%-100%? Is the valve closed throughout the range of 30%-70%? ? It seems that motion control is delayed and highly variable

This post was last edited by Ku Liang Zhi Le on 2019-6-1 at 15:36. It deals with the PIC4021 tower pressure range control system: the controller operates in reverse mode, while PV4021B functions in fail-closed mode (operates when air is supplied); its signal range is 70~100%, and it controls the LN injection valve. PV4021A operates in fail-open mode (operates when air is cut off), with a signal range of 0~30%, and it controls the non-condensable gas discharge valve. During normal operation, the output operating point of the PIC4021 is above 30% (for example, 50%). At this time, both PV4021B and PV4021A are fully turned off. As the tower pressure decreases, the output of PIC4021 increases; if the output change is between 30% and 70%, both valves remain fully closed. As the pressure further decreases and the output of PIC4021 increases by more than 70%, the opening of PV4021B increases (at this point PV4021A is fully closed), the LN injection flow rises, and the tower pressure is restored. As the tower pressure increases, the output of PIC4021 decreases; if the output change is between 30% and 70%, both valves remain fully closed. As the pressure increases further and the output of PIC4021 decreases by more than 30%, the opening of PV4021A increases (at this point PV4021B is fully closed), the flow rate of non-condensable gas discharged increases, and the tower pressure is restored. The operating relationship between the two valves is such that when the tower pressure decreases, valve PV4021A is closed first, followed by the opening of valve PV4021B ； When the tower pressure rises, first reduce the valve opening of PV4021B, and then increase the valve opening of PV4021A.

What does that number in the step control section mean?

This image shows the operating conditions at a certain moment. At that moment, the pressure at the top of the tower was 15.6%, the opening degree of the LN flow injection valve PV4021B was 0.00%, and the opening degree of the non-condensable gas discharge valve PV4021A was 48.0%.

15% should be the output value of the PIC control circuit