Re: Vacuum Gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds by way of Terry Fritz <teslalist-at-qwest-dot-net>" <gerryreynolds-at-earthlink-dot-net>

This has a feel to it of open loop since the controller doesn't have a
target to shoot for like BPS.  I wonder if a counter could be fashioned to
allow you to "dial in the BPS" or if spark duration is what you want to
control, then be able to dial in the spark time (as in pulse width).  A
pulse width comparator might be helpful for the latter.  Closed loop
response would need to be set to account for the response of the vacuum
system.  Instead of an optical sensor by the spark, you might want to pipe
the spark light to the controller so everything could be shielded.

Interesting concept.  have no idea how this would compare in performance to
a SRSG.

Gerry R
Ft Collins, CO

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, July 31, 2003 8:26 PM
Subject: Vacuum Gap


 > Original poster: "Jeremy Scott by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>
 >
 > So I've created my vacuum gap -- PVC electrical 'T'
 > junction and an old vacuum cleaner motor.
 >
 > I've used 3/4" copper pipe with some very thick
 > copper screw fittings on the business ends. I figure
 > if the fittings get too corroded, I'll sand their
 > faces
 > down or buy new ones. :)
 >
 > I've still got this notion in my head of creating a
 > digitally controlled spark gap. I'm still working on
 > the rotary gap, but for now I'm wondering if a static
 > air quenched vacuum gap would be a better candidate
 > for digital control.
 >
 > The voltage and therefore the frequency of gap firing
 > is a function of the pressure and the distance between
 > the electrodes. The distance is fixed but the
 > effective pressure would be a function of how fast the
 > vacuum motor goes. (The one I've got is pretty
 > powerful -- I think it's from a huge shopvac)
 >
 > I thought about affixing a phototransistor to the T
 > junction to sense when the big spark happens. That
 > phototransistor would turn the spark into a digital
 > pulse after buffering some of the noise out
 > with a few discreet electronic components.
 >
 > The frequency and duration of that pulse could then be
 > counted by my Basic Stamp, which could then adjust the
 >
 > speed of the vacuum motor.
 >
 > So for example, suppose I adjusted the gap distance
 > too closely and the plasma-arc channel forms and
 > doesn't go away. (quench failure) The phototransistor
 > would inform the BS of a very long 'on' pulse. The BS
 > would decide that we need more quenching and step the
 > speed of the vacuum motor up until the spark goes
 > away. If there's a too long 'off' pulse, the BS would
 > lower the speed of the motor. So we bounce back and
 > forth between these inputs until the desired breakrate
 > is reached. This is assuming that the gap was set at a
 > 'resonable' (if not exactly right) distance to begin
 > with.
 >
 > If the BS steps the motor to it's highest speed and
 > there is still a quench failure, the BS could then
 > shut off coil power.
 >
 > If there isn't a spark immediately after turning the
 > power on, then it'll step the motor down until there
 > is one, eventually shutting the coil down if no spark
 > when the motor is stopped.
 >
 > Another sensor could be wired into the saftey gap,
 > which would help keep things under control by shutting
 > the coil down if arcs occured there too often.
 >
 > The only issue I see with this setup is that there
 > might be some lag time between changing the motor
 > speed and when that actually affects the air pressure
 > in the gap enough to change the breakdown voltage.
 > If it's a long time, then bad things could happen.
 >
 > What do you think?
 >
 >
 >