[time-nuts] Slightly OT: inexpensive USB analog-digital converter?
bruce.griffiths at xtra.co.nz
Fri Jan 18 17:12:34 EST 2008
Poul-Henning Kamp wrote:
> In message <47911B8F.5050100 at xtra.co.nz>, Bruce Griffiths writes:
>> 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.
> They ARE feedback halls :-)
Yes, but the accuracy is an order of magnitude or so less than is
possible with a feedback hall sensor.
> Their specs are pretty hard to read however.
> The 6A is the "nominal range", but the "measurement range" is three
> times larger (limited by the output voltage).
> They have other models with larger nominal current and correspondingly
> higher range.
> The measurement errors are static and can be calibrated out, the
> major one I found is stray magnetic fields.
Offset drift is significantly higher than for other sensors.
The open magnetic circuit (required to install the Hall sensor)
increases the sensitivity to external fields.
LEM also make dc fluxgate current sensors with 1ppm linearity and 50ppm
Fluxgate current sensors:
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