26 Sep
2004
26 Sep
'04
11:16 a.m.
On Sun, 26 Sep 2004, Gordon JC Pearce wrote:
Tony Duell wrote:
Yes, but I can't remember which end you put the slug at for which action
Normally I'd research this and have the detailed info before responding,
*especially* since I just recommended a lot of books on the Subject - but
after a cursory Google and skimmming thru the texts that are near to hand,
I can't find the actual detailed descriptions of the various
electromechanical 'delay' schemes.
From (faded) memory: If a copper ring is placed over the relay solenoid
near the end, it acts as a transformer, and when the current is removed,
it sets up a 'flux resonance' of sorts, acting to keep the magnetic field
alive - this action decays over a period determined by the various
parameters and physical layout of the relay - so the device delays it's
drop-out for X milliseconds after the excitation voltage drops.
NOW: I seem to recall that which 'end' of the coil (base or springs) has
an effect, and I *think* that the opposite effect - delayed pull-in - can
be gotten by using a soft iron ring in place of copper - the iron
magnetization current is different from the copper coil windings and thus
absorbs energy during the application of excitation current.
Like Tony, I have the Bell System Technical Journal, Vol. 1, No. 1
(1922) thru Vol 47 (1968)... BUT I haven't the time/space/energy right
now to go plowing thru all that just to look this up... maybe this
evening , *if* the project I'm working on is successful....
Cheers
John
And
slugged relays, with a big metal ring in the coil. These either delay
opening or closing, but I can't remember which way round it works.
I believe (without running upstairs to look in 'Telephony' [1]) that you
can arrange for either a slow make or a slow release [1] A great
2-volume set on the UK telephone system, mine is the 1933
edition IIRC. They contain _complete_ schematics for telephone exchanges
(Well, OK, the circuit for each line is drawn once, not <n> times, but you
know what I mean). They were the books that finally let me understand how
telephgone exchanges work, and proved to me the dangers of giving a
simplified explanation (in that I'd read plenty of simplified books on how
telephone systems work and couldn't make any sense of them).
Now, somewhere I have a very old book on telephony and telegraphy that sounds
very similar to that. At least, I hope I still have - after my father went
silent-key around 10 years ago, it seems that a few people had some novel
ideas about what belonged to them (his Bob Dylan lp collection is long gone,
for one thing). It had diagrams of the various sections of the exchange,
slightly simplified, and then another diagram detailing how they go together
(line finders, call routing, stuff like that).
Gordon.