[time-nuts] Power lines and time

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Aug 22 10:23:04 EDT 2005

In message <4309DA8E.9040801 at erols.com>, Chuck Harris writes:

>> Uhm, sorry, that is just plain wrong.  The Ferrantis (sp?) power
>> meter which is the most widely used meter in the world is not
>> frequency sensitive within a band of +/- 10% or more.
>I have never seen a power meter made by Ferranti in the US.   Landis-gyr,
>definitely, but not Ferranti.  To quote Landis-gyr's website:

Sorry, not "Ferranti", but "Ferraris" and not "made by", but "principle".

You can read about it here:


>Here most of our meters are of the induction type, which work on the principles of a
>split-phase induction motor.  They are very easy to recognize by their
>horizontal 4 inch corrugated aluminum disk that rotates (hopefully) slowly.

That is exactly the kind I'm talking about, only they're not exactly split-phase
because the offset fields are current vs voltage.

Their frequency sensitivity is very low compared to other error
factors.  Most of the installed meters are class 2 (ie: up to 2%
wrong) or worse and frequency is seldom allowed to fluctuate +/- 1%
in any civilized grid.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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