LOL... Exactly as this 'long toothed' member indicated in post #17 !
But as someone else mentioned, I believe most engineers know how to use these devices but the contradiction is in the description of contacts.
Signal Descriptions
Regarding my mention of, for example "Start Hydraulics" push-button, where I said the description (of function) should describe the actuated state, I have found other confusing issues when 'info only' signals from E.Stop or guard circuits are documented in PLC input listings and code.
I believe any PLC input signal should describe the meaning of the 'Logic 1' state, but have come across many descriptions of E.Stop input signals poorly described, some just 'symbolized' or described as "Emergency Stop" when in most cases, if derived from a safety switch N/O contact, should be described as "Not E.Stop" or "E.Stop OK" or similar.
Of course, if from a N/C contact from the safety relay, then it should be described something like... "Emergency Stop Activated" or "E.Stop State" or "E.Stop NOK" or similar.
This poorly documented description problem often doesn't end there...
With inputs often documented as...
"Safety Gate"
"Coolant Tank Level Switch"
"Hyd Pressure Switch"
"Over-travel Switch"
Describing the connected device instead of the function.
All having different meanings depending on the logic state of the input, and how the device is wired.
I have often found this to be a problem in PLC code created by someone whose first language may not be English, and the necessary adverbs or adjectives are omitted or used incorrectly. (But sadly, sometimes found in code created by engineers whose first language is English!)
Perhaps missing...
"... Closed"
"... Open"
"... High"
"... Low"
"... OK"
"... NOK"
"... In"
"... Out"
"... On"
"... Off"
<Rant over!
>
Hope this hasn't gone 'off topic' too much.