Topic: The nomenclature of valves and contact states is frustrating

This is nothing about QET, but a general problem i often face:

When a valve let media pass, it is OPEN, when it stop media it is CLOSED.
When a contact let current pass, it is CLOSED, when it stop current it is OPEN.


That makes it a pain to describe and read electric + pneumatic shemas and description in english.

I have to think in terms on and off: wehn a switch or valve conducts they are on ON, when they stop media/current they are OFF.

So when creating master / slave elements for pneumatics, i let a NC normally closed switch represent a NO normally on valve (both hare ON)

That is OK as long as i draw it.  But when trying to explain it i text it get easily weird, you do not say a valve is "ON" in technical texts.. or?...

Brain hurts...

How do you other people think and solve the nomenclature to make it clear?

  • Nuri
  • Nuri
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Re: The nomenclature of valves and contact states is frustrating

Usually, in automation, the texts of PLC input or output signals are related to the PHYSICAL state of actuators (valve, motor, lamp, heating, magnet...) or sensors (contact switch, limit switch, proximity switch...) from a PROCESS point of view, not from an electrical point of view.

The reason is that the programmer of the machine/plant has to know what PHISYCALY happens when a digital output is set from low level (=0) to high level (=1). The electrical state of circuitries is not interesting for the programmer, except when he has to debug something.

For example:

You have to control an automatic door which is CLOSED in the passive state.
This door is opened by a pneumatic cylinder, which is controlled by a pneumatic valve, which is controlled by a 230VAC solenoid, which is controlled by a 24VDC relay, which is controlled by a PLC digital output.
To describe the name of the PLC output, it does not matter to know the state of all components between the PLC output and the door (relay, solenoid, pneumatic valve and cylinder).

It means that the PLC output that controls the opening of the door has to be named:
"open automatic door"
because this text describes the high level of the digital output.
--> this way, the programmer knows that when he sets the output to high level, the door opens.

But... don't forget that electrical diagrams are ALWAYS drawn in the PASSIVE state!

Re: The nomenclature of valves and contact states is frustrating

I totally agree: draw inactive state, and name PLC connections to what they do when active.

Problem comes when i link the opening and closing coils (slaves) on the electric shema, to the 5/3 valve on the pneumatic shema.  (self made elements, see my prototypes at bottom section of the shematic in picture at https://qelectrotech.org/forum/viewtopi … 571#p5571)

Like the PLC signals the active state and connection is named thereafter, similarly I think the best it to have this set up so the coil that makes the pneumatically controlled processvalve open (=media flows) at the master (the 5/3 control valve) is given a symbol meaning open (=media flows) Easy and clear so far.

Problem comes now: QET is targeted electrical, so at the master is shown symbols for open and closed switches.  By switches switch that is letting current through is called "closed" - opposite from the valve.  My current thinking is that for such application i describe here, i should make it show "closed" switches (ON = let current = media through) for the pneumatic coils that open the process valve.

That, for me, seem logical in sense of ON/OFF, it is just the traditional closed/open nomenclature that is illogically inverse in fluids contra electrics, and it is quite disturbing.


( I can dream of a more configurable function i QET so it can show other symbols instead of switches, or words that show up at both slave and in master xref tble, but this way i think i can use what we have )