Relay computers

From: John Lawson <>
Date: Sun Sep 26 11:16:59 2004

On Sun, 26 Sep 2004, Gordon JC Pearce wrote:

> Tony Duell wrote:
>>> 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
> 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....



>> [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.
Received on Sun Sep 26 2004 - 11:16:59 BST

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