Richard Clark wrote:
On Tue, 27 Feb 2007 09:10:12 +0000, Ian White GM3SEK
wrote:

As Owen relates (and so have I) these instrument only sample V
and I on the line - they categorically DO NOT sample power.

Hi Ian,

We've been through this before. No instrument operates in the absence
of power. Simply because you and Owen are graced with instruments
that demand so little, does not negate what power they do rob from
what is available. Even the humble electrometer has to overcome the
force of gravity to open its foil leaves, and climbing that potential
energy hill is work over time - power.

Hammer down the directivity as much as you want, and it will still
resolve to some diminution of power available to the load.

Richard, that argument is otiose.

What I said (in full context) was that their principle of operation as
measuring instruments does not involve sampling traveling waves of power
from the line.

Of course they must incidentally consume some power to move the meter
needle, but that is not part of their operating principle.

For that matter, almost all measuring instruments abstract some energy
or power from whatever they are measuring - but that is usually
incidental. It certainly does not make every instrument into a power
meter.

Can you not see this?


To wave a
hand and say NOTHING does not make it so.

To wave another hand and say traveling waves of power exist does not
make that so, either.




--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek