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Re: Vacuum Gap



Original poster: "bob by way of Terry Fritz <teslalist-at-qwest-dot-net>" <yubba-at-clara-dot-net>

hi Jeremy,
  I would get  in the ballpark first by  running your vacuum cleaner motor 
though a variac and  looking for the longest spark. This will also tell you 
how close the coil is to  being in tune. On my 8'' coil  the  motor speed 
of the vacuum cleaner  motor changes the spark length in a bout 2 or 3 
seconds.  I am using a 1 kw motor with slots cut in the  PVC pipe to allow 
air  to go  right into the  gaps. I have the end of the gap sealed so al 
the air has to go though the  gaps. With 3 kw  driving the coil i  usually 
need about 3/4 power to the motor for best results.

bob golding

  At 07:41 03/08/2003 -0600, you wrote:

>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?
> >  >
> >  >
>
>
>