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Re: EMI Filters

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

Paul,

The DVM test leads make fine receiving antennas for the pulses radiated from
the wiring in your ignition coil setup.  Also, the pulses can travel along
the wiring and around the EMI filter, depending on how you have the filter
grounded - sortof a Tempest Effect.  I have had to put a Wavetek 27XT, set
to read frequency, in a shielded enclosure and only run an optical fiber
into the shield to a circuit that converted light pulses to electrical
pulses to the 27XT.  Without the shield, the 27XT readings would be erratic
and wrong.

Just use analog meters - they are plenty good for most TC related
measurements.  You can buy surplus AC and DC panel meters from many sources.
And you can alter the ranges with shunts or series resistors to suit your
needs.
--Steve
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, May 06, 2005 12:17 PM
Subject: Re: EMI Filters


> Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>
>
> Steve,
> I understand the misbehavior of the DVM. That is where I am confused. I
> thought the EMI filter would prevent the impulses from the ignition coil
> from "backing up" into the mains supply on the other side of the reverse
> wired EMI filter. Thanks.
> Paul
> Think Positive
>
> ----- Original Message -----
> From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> Sent: Thursday, May 05, 2005 11:46 PM
> Subject: Re: EMI Filters
>
>  > Original poster: "S&JY"
> <<mailto:youngsters@xxxxxxxxxxxxxxx>youngsters@xxxxxxxxxxxxxxx>
>  >
>  > Paul,
>  >
>  > Many digital VOMs misbehave when the waveform is anything but a sine
wave.
>  > When impulses are flying around from spark discharges, many DVMs won't
>  > function at all.  If you use an analog meter, you will see that your
>  > measurements are what you would expect.
>  > --Steve Y.