[rrd-users] Energy Metering (Was: Modifying results for GPRINT output)

Simon Hobson 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.

Or ...

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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