P&ID drawing

[Tom749]

Hello. I have one question about the symbol in the P&ID drawing. What are the meanings of the "HOA" symbol. For example, the "SW/HS/XA/XL" marks in HOA. I attach the sample drawing to refer to. Thanks. P.S. If it is possilbe, Can I know the full characters of the abbreviated charater? (SW/HS/XA/XL and HOA)

[TimWilborne]

HOA would stand for Hand (Manual) Off Auto. It looks like you are looking at a 4 pushbutton station with 3 position selector switches in it. As for the other codes, could the be short for some function or output of the machine

[paulengr]

http://www.engineeringtoolbox.com/isa-intr...odes-d_415.html First thing to be clear: ISA notation is somewhat limiting, even in the process industry where it was intended to be used. Nobody I've seen yet in multiple chemical companies and among burner companies follows it to the letter. Although the basic concepts are the same, I have yet to see anyone doing P&ID diagrams using ISA notation "by the book". For instance, "FV" is supposed to be a control valve but 9 times out of 10, I've seen them listed as "CV". Going along with a more common example, it is very common to see "CV" or "FV" for the valve itself. "HS" would be a hand-operated override control. ZSL/ZSH or LSL/LSH would be limit switches for fully opened/closed positions. So we can somewhat use this is a guide for what's going on. If they are going strictly by ISA then HOA means a hand/orifice/alarm. However the common meaning is a 3 position selector switch (hand/off/auto). HS means "hand switch" (seems redundant). SW is meaningless under ISA (speed, frequency; well) but it probably represents the switch (starter?), similar to the control valve example above. X is undefined so "XA" could be an alarm and "XL" a pilot light (going strictly by ISA) or they could be feedback for the auto function or any number of other possibilities. The moral of the story is that P&ID nomenclature is not as standardized as something with an ANSI standard would lead you to believe.

[IamJon]

could hs be hand switch and sw be software? that would be hand and auto...maybe the A in hoa is more like 'plc control' and you can do man or auto from the plc... typically everything in a box (all the symbols you asked about) are in software. so they might all be connected to the hmi. or try this page from acad: http://www.cadtoolsonline.com/pidinstr.htm root: http://www.cadtoolsonline.com/pid.htm Edited January 15, 2009 by IamJon

[IamJon]

Now that I think about it, is it symbols in a box or diamond shaped symbols that are software controlled?

[TConnolly]

X = unclassified - user can use for whatever. XL and XA are indicators. A=Alarm L=Light. I have posted an abbreviated ISA cheat sheet here: http://www.plctalk.net/qanda/showpost.php?...amp;postcount=5 Edited January 16, 2009 by Alaric

[denizen360]

hi will share a complete list of standard p&id symbols.. normally x is unused.. it is user defined.. it changes according to the consultant.. X is user defined... P&ID standard symbols How to interpret p&id drwaings??? Updated one Edited April 12, 2014 by denizen360

[denizen360]

p&id symbol list.. this will help you a lot.. P&ID symbol list