cause effect question ("not open" and "close" difference)

[koba78]

There is Low pressure hopper (above), and high pressure hopper (below), with their XV-00A(loading inlet valve), XV-00B (vent valve).

As start of the transfer, open XV-00A to allow particle to enter the low pressure hopper, then transport gas vent to collection header.

And, XV-00C, XV-00D are transfer valves from LP hopper to HP hopper.

Could you please explain why ZSO-00C, ZSO-00D is described as "not open" instead of close when permissive action required (attached in the post)?

could you please help me out?

Thank you for your help.

 

[KiwiMace]

The valve has limit switches set to switch when the actuator moves through the full range of travel. "Not open" probably means that neither the full open or full closed switches are closed. This in turn implies that the valve is somewhere in the middle, or stuck not quite closed due to material on the seat, or the switches aren't set, or the wiring not done, or the point on the DCS/PLC not defined to the input...

While 'not open' is arguably the same as 'not closed' in a two switch scenario, the 'not open' label would be applied according to the fail safe or operator interest.

 

[ScottyUK]

'Not Open' is possibly a 'b' contact on the 'open' limit switch, with NOT being the logical operator to invert the signal. Depends on who wrote the datasheet.


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