Is there an error in the typical diagram of the XV valve SIS interlock shutdown?
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This post was last edited by Heisenberg on 2021-9-2 at 08:59. Please check whether there are any errors in one of the typical logic diagrams presented in this article. This diagram is designed to implement the SIS interlock shutdown function for FC-type XV valves; it operates in fail-safe mode – no action is taken when the valve is normally energized, but shutdown occurs when the interlock is activated. As shown in the diagram below, based on my understanding, the Open Push Button XSHO is a normally open button, while the Close Push Button XSHC is a normally closed button. Therefore, I wonder if there is an error in applying the NOT operation to the AND gate inputs marked with red boxes in the diagram. In my opinion, that NOT operation should be removed, otherwise the reset signal for the XV valve will remain active, preventing the DCS from opening the valve
This post was last edited by mutianly on 2021-9-2 08:28. There is also a NOT gate after the AND gate; this allows the valve to be opened and closed normally. When an SIS signal is received, interlocking shuts down the valve. When the valve is open, the shut-off signal is 0; when it is closed, it is 1. The normal SIS signal remains at 1. When both signals are 1, the subsequent value is 1, and when they are not 1, the subsequent value is 0. It does not reset (the reset priority flip-flop) – the RS output is 1 ； When the valve is closed, the shutdown signal is 1; when it is not closed, it is 0. The normal SIS signal is 1 when the valve is closed and 0 when it is open; once the valve is opened again, the RS output is reset to 0 ； The interlock SIS signal becomes 0; when it is 0, it is inverted to 1, and the RS reset output is 0. It is important to note that the normal output of the SIS signal is 1, while the interlock output is 0 – this is inverse logic.
Is the Close Push Button a normally open or normally closed button? Does XHSC mean a normally closed node? When the valve is in the open position and no valve-shutting interlock signal is triggered, what is the signal state of the Close Push Button – 0 or 1 – before it sends out a 0 signal? If it is Valve 1, it will automatically reset to output 0, triggering the interlock action.