Ok, so call me lazy, real lazy !
clamp on your probe, measure a number, and then work to reduce that number by
twice what is needed to meet the limit, then re-test.
Repeat, if necessary.
The really big trick in this process is knowing how to reduce the measured
number of the problem that has shown up. Sucks to be you.
ps. I have used that same technique for years. It works really well when done
with relative measurements.
pps. a couple of products needed more than halving the number measured at the
beginning.
ppps. correct fixes usually kill the problem, not just reduce it. But there
are exceptions.
From: Ken Javor <[email protected]>
To: [email protected]
Sent: Wednesday, January 13, 2016 4:25 PM
Subject: Re: [PSES] Current probe for CM currents
Re: [PSES] Current probe for CM currentsI re-read the query and see I didn’t
address the actual question. The current probe inserts an impedance given by
the transfer impedance divided by the winding turns ratio. Once you have
measured the transfer impedance and computed the inserted impedance, you can
then judge the inserted impedance against the cable impedance itself to assess
any perturbation of the quantity to be measured.
Ken Javor
Phone: (256) 650-5261
From: Ken Javor <[email protected]>
Date: Wed, 13 Jan 2016 15:15:55 -0600
To: <[email protected]>
Conversation: [PSES] Current probe for CM currents
Subject: Re: [PSES] Current probe for CM currents
A current probe measures the net current on the conductor within its opening.
The impedance of the circuits attached to that conductor may affect how much
current flows through the conductor, but not the measurement thereof.
Ken Javor
Phone: (256) 650-5261
From: Amund Westin <[email protected]>
Reply-To: Amund Westin <[email protected]>
Date: Wed, 13 Jan 2016 18:48:23 +0100
To: <[email protected]>
Subject: [PSES] Current probe for CM currents
Planning to do some EMI troubleshooting with a «homemade» current probe.
Probing a lot of cables inside a rack and try to find the source.
Will make a current probe by a ferrite core (two halves, a few turns wire and
coax plug) as many EMI experts have posted on the web and on this forum.
Then find the Zt[dBohm], so make a measurement on a cable and verify the
readings on the spectrum.
But when clamping on the current probe, which is a ferrite, does that change
the cable impedance and therefore actually changes the real current flow, so my
reading will not be true? ... or am I missing some fundamental theory here? ...
#Amund
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IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can
be used for graphics (in well-used formats), large files, etc.Website:
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