[rrd-users] Energy Metering (Was: Modifying results for GPRINT output)
linux at thehobsons.co.uk
Tue Sep 4 18:02:42 CEST 2007
Alex van den Bogaerdt wrote:
>I may be asking for help myself soon; I'm thinking about a
>webcam, a led (for illumination) and some ocr software to
>read my own meters. That, or a smarter idea on how to automate
>reading those meters.
I assume then that you still have the old
mechanical "Ferraris Disk" meter. I would look to
see if there's any way you could focus a sensor
on the disk which will have some markings on it -
IIRC there are lots of stripes around the edge
(high frequency, high resolution) and some larger
markings (such as one/revolution). Ideally you
would like to mount a reflective sensor close to
the disk surface, but your utility supply company
will not be amused if you break the seal and
start fiddling with their meter !
If you could achieve this then you'd have just
the same system as the OP - one pulse every X
number of watt-hours.
WARNING - DO NOT try this without adequate knowledge/training !
It may be simpler to install your own private
meter downstream of the main meter. All it
requires is to drop the tails out of your
distribution board, put new tails from your meter
to the board, and put the original tails into the
supply side of your meter.
A quick look around gives a number of suitable
units, generally in the region of £100-£150 (or
something like ¤150-¤220).
Even simpler would be to get a meter unit that
has an external CT (current transformer) and use
a split CT - ie one with a core that splits into
two pieces so it can be put around a cable
instead of having the cable threaded through it.
That would eliminate the need to disturb your
main cables at all as the unit can take it's
voltage feed from an output circuit from the
distribution board, and the CT can be clipped
around a main feed cable without disconnecting it.
If you REALLY want to DIY it (and have the skills
to do it without killing yourself or burning the
house down), then there are chips to allow you to
build your own. See
and in particular
which does all the complicated stuff and has a
serial port !
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