[GreenKeys] Model 15 Selector Magnets

[ad7i]

Greetings --

I'm trying to understand the operation of Model 15 selector magnets.
Several people have told me that there are two sets of coils:  pulling
coils and holding coils.  From this description I can imagine a
mechanical-electric switching arrangement that, when an armature over the
pulling coil is moved by the flux produced by the pulling coil, that the
actuated armature causes current to be routed away from the pulling magnet
and to the holding magnet, which holds the armature in place until current
through that holding magnet is interrupted.  Again, this is the mental
construct I have in my head based on the terms pulling coil and holding
coil.

Yet, when I look at a schematic of a circuit used to control the selector
magnets in a Model 15 (such as shown on PDF page 4 of the document at
http://www.navy-radio.com/manuals/tty/wd/15_wd_drh.pdf, shown below as a
JPG ), I see a selector magnet formed like that of a model 28, as in two
adjacent parallel solenoid coils with opposing windings, carrying the same
current, to form a N-S poll face at either end of the coils (like the open
end of a horseshoe magnet).  Based on the schematic showing two coils that
carry the same current at the same time, with no switching arrangement
between the coils, as shown on PDF page 4 of the above referenced document,
I don't understand how the terms pulling coil and holding coil apply.

[image: m15-selector-magnets.jpg]

I'd be grateful for any info people can share with me regarding the Model
15 selector magnet operation.

Paul, ad7i
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