radiobit@BERNIA.DRAGONET.ES wrote:
>
>         Hi All,
>
> I'm trying to design a power consumption control system for domestic 220V
> 50Hz AC mono phase powered devices. The idea is to get a PIC calculating the
> KW/hour consumed and guess this can be done measuring the current in the AC
> line.
>
> Have seen some current sensors based in hall-effect detectors and a ferrite
> toroidal ring but have no data sheet of this sensors and how to interface it
> to a PIC. Is an A/D a must for this purpose ?.
>
> May be someone in the list has already dealed with this application and can
> illuminate (or flash!) some of the problems I can find in this project.
>
> BTW. Have been reading the list for about a month and think is one of the
> best sites have found in the Internet. Thanks to you all guys.
>
> Luis Fernandez Cormenzana
> RadioBit Sistemas, S.L.
>
> Fax/Tel:+34-6-585 64 57
> e-mail: radiobit@dragonet.es


Three ways to sense current:

1. Current Transformer, CT, may or may not have ferrite core.  Output is
AC voltage isolated from line and usually symmetrical around the
potential of either lead, so you have to deal with bipolar waveform.
2. Hall effect device.  Output depends on type of device but is tied to
the potential of the power supply(ies), so whether it is isolated
depends on how you supply power.
3. Current sense resistor.  Output is AC Voltage not isolated from line.


All of these signals need supporting circuitry and some kind of
digitization.  Don't forget that current and Voltage are out of phase
for reactive loads, and that the current waveform can be distorted
dramatically.

The lowest cost product would probably use a sense resistor and
non-isolated power supply that 'floats' on the line.  Of course, this
requires double insulation for safety.
--

Paul Mathews, consulting engineer
AEngineering Co.
optoeng@whidbey.com
non-contact sensing and optoelectronics specialists