Warning - depending on your application, this type of sensor is only useful
if you can tolerate the AC signal being injected onto the DC line being
sensed. I spent a bit of time looking into similar methods but they all
seemed likely to increase the AC noise level outside our spec. limits.
On the other hand, for measuring a DC current in a less demanding
application, they may be just what you want.
NASA developed a similar system using special magnetics with a very square
hysterisis loop. During the AC transistion an output voltage proportional
to the DC current could be sensed. But it also injected noise.....

Richard P



   There have been posts to this list in the past asking about measuring
large
DC currents without using a shunt resistor. The latest issue of Nuts &
Volts
magazine (April 2004) has an article on page 38 describing the construction
of a transformer based DC current meter with full scale up to 100 amps (and
no, this is not an April Fool's joke).
   The sensor is a toroid wound with 200 turns which acts as one half of a
transformer. The other winding is a single wire passing through the center
of
the toroid, carrying the DC current to be measured. The main (first)
winding
is placed inside the feedback loop of an oscillator made from a voltage
..

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