[time-nuts] Slightly OT: inexpensive USB analog-digital converter?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jan 18 16:35:11 EST 2008

Poul-Henning Kamp wrote:
> If you hook it to a Hall based current-sensor like the LEM LTSR, then
> there is no problem with it.
If a 0.7% accuracy and 6At range suffices.
A feedback hall sensor has better linearity, however they have a
relatively large offset drift.
If not then an optically (or transformer) isolated ADC that can be
floated at the current sense common mode voltage may be necessary.
Depending on the supply output voltage, the operating voltage range of
other high side sense schemes will either be exceeded or the accuracy
will be reduced.

A dc fluxgate current sensor (input circuit is a winding on a
transformer just like a Hall effect current sensor) is perhaps a better
choice in that (if you really need it) accuracies of 1ppm or better are
possible in the current comparator mode.
Commercial dc current fluxgate sensors are not that accurate, however
they have better linearity than hall effect current sensors.
A flux gate sensor has an offset drift about 20x lower than an
equivalent hall current sensor.


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