RE: DRSSTC -- EMI scope problems

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

Original poster: "jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>

Hi Steve,

Thanks for the help. My comments are between yours (no
 >).
--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Steve Conner by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > Original poster: "jimmy hynes by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>"
 > <chunkyboy86-at-yahoo-dot-com>
 >
 >  >The magnetic field from the primary is freakin'
 > out the scope when the
 >  >supply voltage is only 20 volts!
 >
 >  >Is there any way to make good measurements with
 > the 60khz magnetic field,
 >  >or do I just have to hope it doesn't blow up?
 >
 > I had similar problems when doing the OLTC stuff. I
 > have seen a trace that
 > should be a sine wave bent into a series of loops.
 >
 > I believe what is happening is, the magnetic field
 > is inducing a current in
 > a ground loop, either composed of your scope probes,
 > scope, and AC power
 > wiring. Or it could be acting on a ground loop
 > internal to the scope itself.
 > Or the field could actually be strong enough to
 > deflect the beam directly 8-at-
 > Given that your scope showed the noise with no
 > probes connected, and the
 > voltage dial didn't affect it, I suspect one of the
 > latter two.

I thought it might be directly affecting the beam, it
got better when on its side, and no probes attached,
but now with additional input it shows the beam is
just deflected the other way (reletive to the
scope)the sinewaves look like they're almost loops.

 > Things you could try are:
 >
 > *Get some longer probes and move the scope further
 > away
 > *Turn the scope around, on its side, etc, till you
 > find a position with
 > lowest interference
 > *Put iron sheets around the scope :)
 > *Get another scope that doesn't suffer so badly :))

I was thinking about making an extension with TV
cable, because I already tried changing its position,
and it just changed the axis of interference.

 > To reduce ground loops in your probe system:
 >
 > *Put ferrite rings on your probe leads
 > *When using two probes, twist the two probe leads
 > together and only use the
 > ground clip on one of them
 > *Use both channels, clip one of the channels to the
 > ground reference, and
 > use the ADD/INVERT function on the scope to measure
 > the difference between
 > them

How would the ferrite rings help? The stuff I want out
is the same frequency I want to measure! I already
tried the ADD/INVERT thing too, and it seemed to help,
but now that I think of it, it shouldn't have, because
I killed the second channel when it blew up last time.
I didn't think about twisting the two together though,
so I'll try that.

Jimmy


 > Steve C.
 >
 >