[GreenKeys] 1917 thesis on Morkrum

[John Nagle]

> Date: Mon, 15 Mar 2010 21:37:30 -0500
> From: dmm at lemur.com
> Subject: [GreenKeys] 1917 thesis on Morkrum
> 
> I've just stumbled upon a rather interesting, fairly early study.
> It is a 1917 Bachelor's thesis submitted to the Armour Institute of
> Technology (one of the predecessors of the Illinois Institute of
> Technology by Ralph H. Earle.  The title is:
> 
>    "The Morkrum System of Printing Telegraphy"
> 
> It has been digitized, and is available online at The Internet Archive:
> 
> http://www.archive.org/details/morkrumsystemofp00earl
> 
> It is a study of the entire system of equipment.  It has a few
> photographs, and a number of drawings.  It doesn't identify the
> equipment by model/type number (the page printer shown has a
> typewheel mechanism on a moving carriage, and a stationary (well,
> rotating but otherwise stationary) platen.  I'd be curious to learn
> what the model/type numbers were for the equipment shown.

    The original Morkrum system is interesting.  You can see them struggling
with the synchronization problem.  The early Morkrum machines were not
start-stop; the distributors at both ends turned constantly.  The
receiving distributor turned slightly faster, and there was a device
to slightly retard the receiving distributor when a START pulse came in.
This class of mechanism tends to come into sync if it gets out of sync.
It's half of a phase-locked loop, and very similar to analog TV vertical
hold control circuits.

    The Morkrum machines had far more electrical parts than the later
Teletype machines.  There were about 16 relays and six magnets
in the Morkrum machine.   Later machines were simpler electrically
and had more mechanical logic.  The Model 12 also had relay decoding
of incoming characters, with one magnet for each bit.  The Model 15,
with all decoding done mechanically and only one selector magnet,
had the fewest electrical parts.

    The tradeoff is interesting from an engineering perspective.
Most relays required adjustment until the telephony industry
finally developed wire relays around 1940.  A device with
timing-sensitive relays in the pre-oscilloscope era was
inherently tough to adjust.  With the mechanical machines, all
timing came from a main camshaft.  So if the motors could be
kept roughly in sync, and the one selector magnet was adjusted
properly, the adjustment problem became manageable.  So Model
15s could be produced in volume and used in the field.

				John Nagle