That is why it is very difficult to make current probes well shielded
enough and certainly with a flat transfer impedance that covers a few
decades of frequency. The cost of a good current probe, for instance an
F-33-1 or F-61 is less than what it has already cost your company in
time lost.
Doug
Douglas C. Smith
University of Oxford Course Tutor
D C Smith Consultants
PO Box 60941
Boulder City, NV 89006
Email: [email protected]
Web: http://www.dsmith.org
Web: http://emcesd.com
Tel: 702-570-6108
Mobile: 408-858-4528
On Sun, 31 Jan 2016 17:49:08 -0600, Ken Javor
<[email protected]> wrote:
You needed a metal shield to prevent capacitive coupling.
Ken Javor
Phone: (256) 650-5261
> From: Amund Westin <[email protected]>
> Reply-To: Amund Westin <[email protected]>
> Date: Sun, 31 Jan 2016 20:21:48 +0100
> To: <[email protected]>
> Subject: [PSES] SV: [PSES] Fwd: [PSES] Current probe for CM currents
> > A clamp-on ferrite with a few turns of wire and connected to a spectrum
> analyzer, worked out to be a good tool for measuring CM currents on single
> cables. It gave me some measured numbers [dBuV], and then I worked
on trying
> to get the numbers down :)
> > But when I placed the home-made probe on wires / cables inside a
noisy rack,
> problems started. The probe picked up almost all kinds of frequencies, even
> when no cables or wires where going through the probe (ferrite).
> > > > This lesson told me that a simple home-made current probe
works good on a
> stand-alone cable, but it does not work that good then measurements are
> carried out closed to other noisy sources. Then you might need a more
> professional current clamp.
> > > > #Amund
> > > > > > > > > > > > Fra: Ken Javor [mailto:[email protected]]
> Sendt: 15. januar 2016 17:53
> Til: [email protected]
> Emne: Re: [PSES] Fwd: [PSES] Current probe for CM currents
> > > > I think it is important to not lose sight of the original
query that started
> this thread. The query was about whether placing a current probe around a
> cable perturbed the current to be measured.
> > There is no doubt that radiated emissions can originate within an
equipment
> enclosure separately from driving common mode currents on a cable, but that
> wasn't the query. In fact, the poster was probing cables within a
large rack
> (enclosure) looking for a source within an enclosure.
> > Ken Javor
> Phone: (256) 650-5261
> > > > _____ > > From: Bill Owsley <[email protected]
> <mailto:[email protected]> >
> Reply-To: Bill Owsley <[email protected] <mailto:[email protected]> >
> Date: Fri, 15 Jan 2016 07:26:08 +0000
> To: <[email protected] <mailto:[email protected]> >
> Subject: Re: [PSES] Fwd: [PSES] Current probe for CM currents
> > If you can measure common mode noise on a cable, you have a
problem from the
> port !!
> Note the world famous Ott's math on this effect in his 1st edition. Might
> be in his 2nd too.
> > I have used both e-field and h-field (current clamp) at the same time.
> We are engineers so figure out how I did that!
> And since some of the work is below 30 MHz, I have also added a
loop antenna
> for a 3rd measurement.
> My approach is if I find any emission, locally, near field, bench stuff,
> that varies by position over the area of the product, then I have a
problem.
> E-field scan,using a o'scope probe. H-field scan usually using a personally
> built small loop, and any other sort of scan, conducted or radiated, that I
> can make up at the moment.
> I work for a homogeneous field in the scans over the area of the product.
> My assumption is that if I find a homogeneous field, then there are no or
> low emission gradients which can equate to a field at a distance. So get
> creative, and redundant, by different methods for measuring the emissions.
> Ironic, I am good at mashing all emissions, and then they hand me an
> intentional radiator and ask that I don't kill the fundamental. What ? You
> mean I have to pick what to mash, and what not to mash?
> Ok, so I caught on quick enough to keep the job.
> > > ps. I suffer from not being able to use a leaky enclosure. I
don't get any
> shielding for the products.
> Cable shielding that is bogus terminated, but at the low frequencies of
> interests, it works.
> Then I have to deal with the higher frequencies, the harmonics !!!
> Plastic covers and pcb and cables up to 15 KW or more of digital BS to make
> an analog signal.
> And then 'normal' digital signals for the ADC circuits all in the middle of
> this.
> Management is like, we have done it this way for over 25 years and
so we are
> not changing it now.
> It works (I have to make it work) so don't change anything. Sucks to be me
> - but I do like a challenge.
> > > > > > > > > > > > > > > > _____ > > > From: Ken Wyatt
<[email protected] <mailto:[email protected]> >
> > -
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