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

[Bruce Griffiths]

Poul-Henning Kamp wrote:
> In message <47912452.1060702 at xtra.co.nz>, Bruce Griffiths writes:
>
>   
>> Offset drift is significantly higher than for other sensors.
>>     
>
> On the LTSR they've pinned out the reference, so you can calibrate
> the offset out.  I've done it, it's trivial.
>
>   
The dc offset for zero input current is primarily determined by the
reference voltage however it  isnt the only source of offset or drift drift.
The hall sensor, the amplifiers and the magnetic circuit all contribute
to drift.
None of these effects can be compensated by having the reference available.
Not having a demagnetising winding for the magnetic core is a major
drawback should the core be magnetised as a result of overload or other
accidents.
>> LEM also make dc fluxgate current sensors with 1ppm linearity and 50ppm
>> accuracy.
>>     
>
> And I belive, they also make money on those.
>
> For my needs (a 12 bit ADC) calibration is just fine.
>
>   
As always there is a cost/complexity/accuracy tradeoff.


Bruce