In article , Paul snipped-for-privacy@topmail.co.uk says... .....
But most engineers are just like children, only really like things that make noises, flash or better still explode. Just like trying to teach science to teenagers.
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It most likely wouldn't work very well. A really wide trace of plane smears out the location too much.
With most of us being in the Wild West I am surprised nobody came up with the obvious: Take a Smith&Wesson and blast holes into it until the current drops. That's where the short is. Or rather, was. Just kidding ;-)
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So I assume this uses the inductive reactance (instead of resistance) to create a voltage gradient when the test current flows along the line ? That 1 MHz test frequency sounds quite low, since a PCB track would have XL about 0.01 ohm/mm @ 1 MHz, so the XL for a 100 mm track would only be about 1 ohm. The signal generator output impedance would have to be well below the typical 50 ohms in order to create a significant voltage at the feed point.
Of course the probe can contain a high gain RF-amplifier to get meaningful reading. Using RF would eliminate the problems of measuring very low DC voltage gradients along the line (such as amplifier offset drift and galvanic voltages caused by dissimilar metals).
Paul
A possible difficulty with RF is it couples just as well through capacitance as through inductance. You might get many false positives. I seem to recall H-P many years ago, sold a probe with a Hall effect device in the tip. You could put a small, controlled DC into the short, & see which traces it was flowing through. Maybe such a device could be made up today: there are small Hall-effect ICs around.
Capacitive coupling can be an issue if the probe has a high input impedance. A probe using a small pickup coil for measuring the magnetic field created by the RF_current_ or measure directly the voltage gradient along the PCB track inductive reactance, could have a low input impedance and the capacitive coupling should not be an issue.
Paul
Ferrofluid --- basically a fine suspension of iron particles in oil, I think. The "spiky soccer ball" is pretty characteristic of what it looks like near a magnet. I think the spikes are not originally from the shape of the field, but because the surface is somewhat unstable in a strong enough field.
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