Re: [EE] measuring the magnetic field from a small trace carrying a < 50uA load?

At 08:02 PM 2025-01-02, you wrote:
>When developing battery powered devices, sometimes it can be difficult to
>track down where the last few dozen microamps of load are being drawn.
>
>One can resort to systematically cutting traces and desoldering components.
>But that is destructive, labor intensive, and error prone.
>
>I would like to know if an active probe exists that can measure and
>discriminate the current/DC magnetic field of small < 50uA loads on small
>but loosely packed PCB traces.

Just as a sanity check- the field 1mm from a wire conducting 50uA is of
the order of 10nT if I did the math right.

I think detecting that with something like a semiconductor Hall sensor is
a couple orders of magnitude too drifty and noisy even if you could deal
with the Earth's magnetic field (tens of thousands of nT) in the vicinity
(maybe by holding it fixed and turning the power on and off). Or build
some Helmholtz coils.. we were able to cancel the Earth's field in a ~150mm
cube fairly well but it took a bit of cost and doing.

Best regards,
Spehro Pefhany


https://news.harvard.edu/gazette/story/2007/04/frank-h-westheimer-major-figure-in-20th-century-chemistry-dies-at-95/