Re: Re: Confused by Current Cost

[Phillip Harris <phil@xxxxxxxxxxx>]

The problem here is that current transformers - although very simple -
are difficult to make perform accurately especially when you need to split
the CT coils which you need to do to allow the end user to "fit"
them - otherwise you'd need to remove the live feed to feed it through a
solid core CT. If you could use a solid core CT then they'd be much more
accurate for the same price.

Certainly when trying to make them cheap enough to be used as a component
in a domestic "toy" meter (which these are) then it's no surprise
they're inaccurate (and I have experience of the problems of designing the
split CT for one of these meters).

At the end of the day these meters are just a guide as to your usage - as
someone once told me about the gauges on a TVR dash "They just give
you an idea about what's going on - it's not the actual numbers they show
that are important but any deviations from those normal figures" ...
so in the case of the Current Cost if it reports one month that you've used
100kw and then the next month that you've used 80kw then you can be
confident that you've saved yourself 20% but the actual consumption
calibration *WILL* be way out.

More worrying though is - as Keith has said - the discrepancy between the
meter and the .xml file ... that shouldn't happen!

Phil

On 2 Jul 2010, at 10:13, craig wrote:

>> Maybe the history suffers from similar discrepancies?
>
> My personal experience of these 'clamp on transmitters' is they are
very
> inaccurate, when compared to the actual meter reading.
>
> My actual consumption, as read on meter for last 7 days is 125kWh
>
> My current cost display says 107kWh (-17%)
>
> I also have a Hmmm device (free from npower) that says I have used
156kWh
> (+25%) over same period.
>
>
>
>
>
> ------------------------------------
>
>
> Yahoo! Groups Links
>
>
>


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