How to draw the valve switching interlock on a PID diagram
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For example, there are four instruments: XV-001, XV-002, XV-003, FV001, and FT001. When there is no flow in FT001, FV001 is turned off while XV-001 is turned on; after 20 seconds, XV-001 is turned off and XV-002 is turned on. After another 20 seconds, XV-002 is turned off and XV-003 is turned on. At the same time, FV001 is turned on again. How should this sequence of operations be represented in a PID control system? Should all five components be connected? If so, what type of control should be specified – flow rate or time interval?
The PID diagram and the interlock diagram are separate.
Just connect the PID; the actions of the other switches are not reflected
Is it enough to connect all the valves with dashed lines?
Is it enough to connect all the valves with dashed lines?
Is it enough to connect all the valves with dashed lines?
So on the PID diagram, these valves should be shown as being interconnected in this way
If the operation of this valve is triggered by a certain signal, such as your flow rate, connect that signal source to the valve using dotted lines; if it’s not that kind of relationship, simply place a valve there
Of course, if you want to create a chain system, you can also add a chain element I; each valve is then connected to the next valve through this I element
The interlocks mentioned above are indeed represented in the interlock logic diagram; a marking symbol can be added in the PID