Go Back  PPRuNe Forums > PPRuNe Social > Jet Blast
Reload this Page >

Open, Off, Closed, On?

Jet Blast Topics that don't fit the other forums. Rules of Engagement apply.

Open, Off, Closed, On?

Old 12th Mar 2014, 21:27
  #1 (permalink)  
Thread Starter
 
Join Date: Dec 2000
Location: Forced retirement
Posts: 1,157
Open, Off, Closed, On?

Whilst browsing through the pages of my new 737 manual (Long, sad story involving 757 fleet reduction) I started to wonder why there is a growing mental block in my noggin with regards to circuits and switches being on, closed, off or open.
Closed circuit TV. Which bit is closed?
If a wire goes "Open circuit" then electricity flows within it so 'Open' must be tied to 'On'. But if I 'Close' a switch it also turns something 'On'. The more I think about it the more addled my grey matter becomes.

Then I looked at the 737 pressurisation system pictures.
If both systems fail you get an "AUTO FAIL" light to tell you that the afore mentioned systems have failed but if the "AUTO FAIL" AND "ALTN" light come on it is trying to tell you that the Altn system IS working.

Am I failing to grasp some hidden logic or has the world gone mad?
blue up is offline  
Old 12th Mar 2014, 21:42
  #2 (permalink)  

Aviator Extraordinaire
 
Join Date: May 2000
Location: Oklahoma City, Oklahoma USA
Age: 72
Posts: 2,394
No it,'s not you. The world has gone mad.

Started when the FE was done away with.

They handled those sort of things.
con-pilot is offline  
Old 12th Mar 2014, 21:50
  #3 (permalink)  
 
Join Date: Apr 2010
Location: Canada
Posts: 2,897
Not a big jet driver, but to electrical types, an open circuit is one in which no current flows, and closing a switch does let current flow. These terms derive from the days of knife switches like this (as seen in 'Frankenstein').

This switch is 'open'

Naturally this conflicts with the plumber's use of 'open' and 'closed' for valves - open valves allow flow, etc.



So - electrical: switch open = OFF, pipes: valve open = ON

Of course, almost all your valves are now moved by solenoids, which connect to electrical switches in the cockpit, so f#ck knows which terminology won out at Boeing.

In reality, your problem is with the manual writer who either doesn't realise this, or doesn't care about your cognitive issues, or more likely each section was written by a specialist in that area and Messrs Boeing consider it your job to understand everyone else's. You are a Sky God after all

As to the indicators, I would have the Auto Fail caption to be Amber (or Red), to show an abnormal condition, and have the ALTN caption Green or Blue to show a normal state (given the Adjacent Amber).

But what do I know?
Fox3WheresMyBanana is offline  
Old 12th Mar 2014, 21:54
  #4 (permalink)  
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 62
Posts: 1,099
If a wire goes "Open circuit" then electricity flows within it
Ah but electricity does not flow through an open circuit only a closed circuit, even if it is a "short" circuit which is a fault condition where the circuit is "shorter" than normal!

We do not actually use the terms "ON" and "OFF" in the leccy industry referring to switches, just "CLOSED" and "OPEN".
west lakes is offline  
Old 12th Mar 2014, 21:55
  #5 (permalink)  
Dushan
Guest
 
Posts: n/a
If a circuit is "open" then the current cannot flow and therefore whatever is energized by it is in the "off" state.

Conversely, if the circuit is "closed", then the current flows and energizes the device, thus making it "on".

YMMV…
 
Old 12th Mar 2014, 22:06
  #6 (permalink)  
 
Join Date: Oct 1999
Location: UK
Posts: 3,336
CCTV? TV that is not broadcast. The camera and screen that displays the image are one complete 'closed' system.

'Open' circuit - a circuit which is incomplete. Current needs a 'complete' circuit to flow around. Break the circuit by 'opening' it (putting a gap in it) prevents current flow.

It's all perfectly logical.

Now, consider a railway signal (semaphore arm or colour light). It is either 'on' or 'off'. When the signal is 'on' it's at 'danger', its fallback position and the position it will revert to if the operating mechanism fails. Only when the signalman pulls it to 'off' may a train pass it.

How about magneto switches. 'Up' for 'mags live', which might seem counter-intuitive when you think of the domestic light switch which is 'down' for 'on'. But the mag switch works the same way as the light switch - when it's 'down' it completes an earth circuit to the mag's low tension coil output, disabling the mag. When it's 'up' the switch is 'off' or 'open circuit', enabling the mag to operate as its coil output is no longer tied to earth.

Again, logical.

And fail safe; if the switch drops to bits or the wire breaks, the mag is 'live' (coil output not earthed) and the engine keeps running.
Shaggy Sheep Driver is offline  
Old 12th Mar 2014, 22:24
  #7 (permalink)  
Dushan
Guest
 
Posts: n/a
Originally Posted by Shaggy Sheep Driver View Post
How about magneto switches. 'Up' for 'mags live', which might seem counter-intuitive when you think of the domestic light switch which is 'down' for 'on'. But the mag switch works the same way as the light switch - when it's 'down' it completes an earth circuit to the mag's low tension coil output, disabling the mag. When it's 'up' the switch is 'off' or 'open circuit', enabling the mag to operate as its coil output is no longer tied to earth.
Maybe in Cheshire. In NA they are up for on, and down for off. Logical.
 
Old 12th Mar 2014, 22:29
  #8 (permalink)  
 
Join Date: Jan 2008
Location: The Smaller Antipode
Age: 85
Posts: 16
Started when the FE was done away with
Totally agree, they also knew where the best bars and cheapest breakfasts were !

........so f#ck knows which terminology won out at Boeing.
In similar vein .......worked for a UK company that purchased a second hand US 747 freighter, and the UK CAA made us go through the US FAA manuals and change every incident of 'warning lamp' to 'warning light' ( or was it the other way around ?)

Yes, World's Gone Mad.
ExSp33db1rd is offline  
Old 12th Mar 2014, 22:30
  #9 (permalink)  
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 62
Posts: 1,099
Maybe in Cheshire. In NA they are up for on, and down for off. Logical.
Careful Dushan, you'll start another us (as in us not U.S.) vs us hamsterwheel
west lakes is offline  
Old 12th Mar 2014, 22:40
  #10 (permalink)  
 
Join Date: Oct 1999
Location: UK
Posts: 3,336
In Cheshire we have Tiger Moths and Chippies. 'Up' for mags 'on', switch open circuit. Same in the Citabria.

If Bellanca in NA can get it right, why not NA domestic sparkies?
Shaggy Sheep Driver is offline  
Old 12th Mar 2014, 22:43
  #11 (permalink)  
Thread Starter
 
Join Date: Dec 2000
Location: Forced retirement
Posts: 1,157
So, when something is described as "having gone Open circuit" it is a broken wire rather than one that has earthed itself and popped the fuse? You learnt summat new every day!

As to the 737 thing, it's a miracle that they haven't had any accidents with such a confusing set of lights. Thank heavens this is just a single isolated issue.




PS. Lone Ranger. Full time flyer, part time airframe restorer and cowling wheeler. (No electrics stuff)

PPS. Has anyone here flown a Chrislea Super Ace?
blue up is offline  
Old 12th Mar 2014, 22:54
  #12 (permalink)  
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 62
Posts: 1,099
So, when something is described as "having gone Open circuit" it is a broken wire
By jove you've got it

rather than one that has earthed itself and popped the fuse?
That's a short circuit
west lakes is offline  
Old 12th Mar 2014, 23:06
  #13 (permalink)  
 
Join Date: May 2001
Location: Newcastle/UK
Posts: 1,473
Just to make life more complicated when I worked as a Cable TV (RF Frequencies) ,maintenance bloke, a open circuit would have been described as a high impedance mismatch a short circuit as a low impedance mismatch when one circuit got mixed up with another it was called a interline.
tony draper is offline  
Old 12th Mar 2014, 23:09
  #14 (permalink)  
 
Join Date: Apr 2010
Location: Canada
Posts: 2,897
swap the word 'impedance' for 'resistance' and the cable circuit is the same as an electrical circuit.
Fox3WheresMyBanana is offline  
Old 12th Mar 2014, 23:17
  #15 (permalink)  
 
Join Date: May 2001
Location: Newcastle/UK
Posts: 1,473
I know but RF can jump across gaps,anyway we blokes wi dirt under our nails just called em shorts and opens mixed up circuits crosstalk like everybody else.
tony draper is offline  
Old 13th Mar 2014, 10:36
  #16 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
Originally Posted by west lakes
That's a short circuit
- what, pray, is a 'long' circuit?
BOAC is offline  
Old 13th Mar 2014, 11:14
  #17 (permalink)  
 
Join Date: Aug 2001
Location: UK
Posts: 1,803
It's all perfectly logical.
when you think of the domestic light switch which is 'down' for 'on'.
But on the domestic consumer unit all the MCBs and RCD are 'up' for 'on'.
spekesoftly is online now  
Old 13th Mar 2014, 11:21
  #18 (permalink)  
 
Join Date: Apr 2010
Location: Canada
Posts: 2,897
..and what about 2-way light switches on stairs? - they could be UP or DOWN for ON

I wonder what the A380 manual says about those....nightmare
Fox3WheresMyBanana is offline  
Old 13th Mar 2014, 11:24
  #19 (permalink)  
 
Join Date: May 2001
Location: Newcastle/UK
Posts: 1,473
Came across key operated switches on equip bays on one job that were marked Enable for on, for the life of me I cant remember what off was marked but I dont think it was disable.
They could have saved on engraving had they just been marked off and on.
tony draper is offline  
Old 13th Mar 2014, 11:44
  #20 (permalink)  
 
Join Date: Apr 2010
Location: Canada
Posts: 2,897
Ford flipped the switch which he saw was marked "Mode Execute Ready" instead of the now old-fashioned "Access Standby" that had so long ago replaced the appallingly stone-aged "Off."
'So Long, and thanks for all the fish' - Douglas Adams
Fox3WheresMyBanana is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.