Re: Oscilloscope question

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Darin,

At 03:46 PM 11/15/2001 -0500, you wrote:
>I have a 3kv 40ma inverter for a neon sign licence
>plate. I would like to use it to make a VERY
>small coil. I need to find out the frequency
>of its output but dont have access to an
>oscilloscope. I've tried to make a Cockroft-Walton
>voltage multiplier to make a DC coil but it
>appears that this wont work. Every time I
>discharge the circuit it makes the inverter
>stop working and I have to disconnect the
>power and reconnect it. Any info as to why
>this happens would be great and I wont have
>to try to figure out what Im going to ask next.

It may have some kind of protection circuit in it that turns it off if the
load is doing something odd.  That may be hard to fix since it is probably
potted in plastic so you can't tear the circuit out.  Maybe adding a
resistor in series with the output would help.

>
>I have found an oscilloscope program that uses
>a PC's sound card mic input for the signal input.
>Does anyone know how I could safely test
>the inverter using this? Im not to crazy about
>puting 3kv into my pc, but if there is some
>simple circuit I could put between the two
>to effectivly step down the output with out
>altering the signal that would be awsome.

I am not sure you need to know the frequency...  The computer will only go
from 50Hz to 20kHz.  Can you "hear" the frequency?  If it is higher than
you can hear it probably won't work with the PC.  However, simply a piece
of wire from the mic input lead sort of near, but certainly not touching,
anything will act like and antenna and record the signal.  Then, many sound
programs will tell you the time between the cycles of the waveform and all
that like a scope would.  You program should do that easily.  If the
inverter makes noise, just try to pick the sound up with the mic.  If the
frequency is high, the mic input may not have much resolution.  I would not
make any direct connections unless you really know what you are doing.
There is no room for error and there are hidden things that could go wrong.
 I would worry about ground noise and high frequency stuff going into the
mic input.  It was never meant to be connected to a high-voltage
high-frequency source and thus has zero protection.

Cheers,

	Terry


>
>
>Thanks,
>Darin
>
>
>