[GreenKeys] Of current loops and voltages.. (M15 20mA / 60mA)

[drlegendre .]

When I began my M15 project, I was under the impression that all of these
machines required the 'standard' 120V DC / 60mA loop supply. In short (no
pun..) 120VDC squeezed through a 1K8 - 2K resistor.

Also was expecting to find a ~50R selector magnet coil. What I found was a
dual-coil setup that - through the miracle of DPDT - allows the machine to
run at 20mA or 60mA.

So if 120VDC / 2K was the expected supply for the 60mA setting, what
open-circuit voltage / resistance was expected for the 20mA setup?

Finally, did I just waste a lot of time building my RS-232 -to- 120VDC /
60mA converter? Could I have just as well used one of the recently rebuilt
Camiacs Mdl. V RS232 -to- 20mA converters already in inventory?

IIRC, the Camiacs supply an o/c voltage of 24 VDC - seems low, in that the
selector magnets are in series in the 20mA position, which means the
inductances sum, and as such, should produce a lot more resistance to
current rise across the windings?

(In the real installation, the lines are very short, a matter of a few feet
- so it's not like there are any long-line effects to worry about. But
what's the theory?)
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