[GreenKeys] LTSpice

[Jim Haynes]

On Sun, 21 Jul 2013, Ralph Mowery wrote:
>
> In it was a mention of the snubbing circuit and that it would contribuit to 
> the marking bias. It did not mention anything about how much or what values 
> to use.  Just very little info on that part of the circuit.
>
It's a complicated situation.  If you start with the 120V 2K ohm loop,
from the instant you close the contact there will be a delay before the
selector magnet pulls in, because of the inductance.  And the inductance
is increasing as the magnet pulls in and the air gap is reduced.  With
no snubber (and there always is something snubbing, or the voltage would
rise to infinite) then the magnetic field collapses instantly and only
inertia and perhaps residual magnetism retards the selector magnet falling
away.  This would produce a spacing bias, the magnet being slow to pull in
and fast to drop out.  Or maybe that is compensated for in the design of
the mechanism.

So it would seem that if you want pull in and drop out to be as 
symmetrical as possible you would want to use a snubber that lets the
voltage rise to twice the supply voltage and maybe discharge through
2K ohms so that the time constants for pullin and dropout are equal.
Slowing the dropout would certainly add a marking bias compared to
the situation where the dropout is not snubbed.