Re: Vacuum Gap

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

Original poster: "Jeremy Scott by way of Terry Fritz <teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>

Yeah the BPS would be dialed in -- the BS2p40
microcontroller has a command which can measure
the width of a pulse (PULSIN) -- This would
let me measure gap conduction time and could
probably let me measure the relative
resistances/reactances of various tank configurations.
According to the manual, the BS2 can measure pulses
with .75 microsecond resolution to 49 milliseconds.
(Stores the result in a word, 65535 possible values)

There is also the COUNT function which will count
the number of pulses that occur in a range of
287us to 18s. Minimum pulse width is 1.20
microseconds.
It can measure frequencies (square wave) up to 416Khz,
so I think accurate feedback for a 120BPS gap is
possible. I probably wouldn't set the sampling rate
at one second, maybe like two AC cycles (33ms or so).

This assumes of course that I properly sheild
everything and run the digital circuitry off
batteries etc..

I was thinking of using a regular LED as a photodiode,
or using an IR phototransistor as I can't seem to
locate any visible light ones right now. (Spark gaps
emit some IR light right?) My PVC T junction will be
mostly dark inside when there is no spark. Maybe a
little ambient light from the glowing copper
electrodes. :) I'll probably use a lens or at the very
least some black plastic 1/4" hollow tubing to keep
the sensor far away from the gap, but close enough to
detect a break.



--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > 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?
 >  >
 >  >