Re: SRSG v. DC-RSG

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Dan,


ARSG tachometer circuits are a bit tricky because of the horrendous EM & ES
environment.  The easy way is to go to radio shack and buy one of their
little DC motors, couple it to the rotor shaft, and use a big analog DC
meter, with appropriate scaling resistors, to read out RPM (or you can
calibrate it in BPS if you wish).  Be sure to ground one of the wires from
the motor, or use a grounded shielded pair, to minimize the HV RF at the
meter end.

A more sophisticated way is to couple to the rotor shaft another little disk
with one hole per rotor electrode.  The disk interrupts a red LED shining on
a fiber optic cable.  At the other end of the cable is a phototransistor
with emitter follower which goes to a frequency counter.  I have used a
Wavetek 27-XT, but I had to put it in a shielded box made of hardware cloth
to avoid bad readings caused by the nearby TC inducing noise into the 27-XT.

Recently I built a dedicated frequency counter, battery powered to avoid the
noise pickup through the AC power lines, to free up my 27-XT.  If you want,
I can send you a schematic.  It uses common CMOS ICs and 7 segment LED
displays.  The fiber and phototransistor items are available from Jameco
(www.Jameco.com).

--Steve Y.
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, December 02, 2004 6:09 PM
Subject: SRSG v. DC-RSG


> Original poster: "Daniel A. Kline" <daniel_kline@xxxxxxxxxxx>
>
> Hi All,
> For the first time in several years, I'm about to add a rotary spark-gap
> to a system. The last time I used a rotary spark-gap, it was
> asynchronous, and didn't work well with the setup I had.
>
> This time I'm using a 1.5KVA potential xformer at 14.4kV, and I'll be
> testing Maxwell caps and MMC configurations to see which is best for
> this particular coil.
>
> I'm wondering if I should try a variable break-rate rotary-gap on a DC
> motor, or if I should try a synchronous rotary-gap.
>
> The reason I ask is because I had a cap explode when using an
> asynchronous rotary-gap, and I'm concerned that the same thing might
> happen if, while testing,  I'm continuously varying the break-rate using
> the DC-motor rotary-gap.
>
> I have DC motor handy, and I don't have a sync motor yet, but I've been
> wanting an angle-grinder for a while now, so it wouldn't take much
> convincing for me to go out and get one for machining the appropriate
> AC-motor armature ;)
>
> Also, does anyone know of a decent tachometer circuit I can use in
> conjunction with the DC-motor in case I go that route?
>
> Thanks,
> Dan K.
>
>
>
>