New (maybe) method for SRSG adjustment

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

Original poster: "Steve White by way of Terry Fritz <twftesla-at-uswest-dot-net>" <slwhite-at-zeus.ia-dot-net>

I am fairly new to coiling (6 months) and am in the process of building my
first coil. The first component that I fabricated was a SRSG because I
considered it the most complex part. My SRSG uses a 1/2 HP 3600 RPM motor
modified to be synchronous. The rotor is 11" with 4 flying electrodes. The
flying electrodes are 1/8" tungsten. There are 4 stationary electrodes. The
stationary electrodes are 5/32" tungsten. The design firing rate is 240 BPS.
After fabricating and assembling everything, I then faced the task of phasing
the firing points properly with the 60 Hz sine wave. I have read about various
methods for doing this. Most involve strobe lights or trial and error. I was
always somewhat uncomfortable with strobe lights because I could not see
exactly where the strobe was firing in relation to the 60 Hz sine wave (zero
crossings, peaks, other). The strobe light circuits also seemed rather
complicated. What I offer here is a method that I have not read about in the
discussion threads. If I am re-inventing something I am sure someone will let
me know.
 
My device relies on one of the U-shaped optical sensors available from various
sources. Mine is made by Omron and I got it from Digikey. One side of the
sensor has an emitter while the other side has a detector. When an object
passes between the emitter and detector current does not flow. They are
available in various gap widths and operating frequencies. The particular one
that I used has a 5.2 mm gap and will handle up to about 100,000 BPS. Follow
the application notes and connect 2 current-limiting resistors, one for the
emitter and 1 for the detector. There will be a power line, ground line, and
sense line coming from the circuit. I then mount this trivial circuit (3 parts)
on a small PC card and epoxy that to an L-shaped metal bracket. I can then
clamp the assembly temporarily to my SRSG base plate. What you want to do with
this device is to allow the flying electrodes to pass through the U of the
sensor thus breaking the light beam each time a flying electrode rotates
through it. I connect the sense line from the detector to the "external sync"
input of my oscilloscope. I connect the 60 Hz power line, suitably voltage
divided, to the scope's vertical channel. When I start up the SRSG, you get a
beautiful triggered view of the 60 Hz power line on the scope. You can then
rotate the motor while it is running and finely adjust the firing point until
it is perfect. In case that I didn't make it clear, there is no high voltage
applied to the SRSG during this calibration. After calibration, just tighten
the motor and you are done. Unclamp the optical detector assembly and put it
away for your next SRSG calibration task.
 
The advantages in using this method are as follows. A very simple circuit is
needed (3 parts) and it is very cheap (less than $5). The firing point in
relation to the 60 Hz sine wave can be seen very precisely on the oscilloscope.
The only disadvantage that I can see is that this method requires an
oscilloscope. The scope can be very low grade though. Mine is single channel
and only about 1 MHz bandwidth. It must have an external trigger. Alternately,
you could use a dual-channel scope and display the 60 Hz power line on one
trace and the optical trigger signal on the other channel. You can then see the
precise relationship between the two.
 
I hope that this proves useful.