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Hot Wire Metering
Subject: Hot Wire Metering
Date: Thu, 29 May 97 19:25:56 EDT
From: pierson-at-ggone.ENET.dec-dot-com
>Measuring the input power to a Tesla coil is not an easy job if you
>want accuracy.
Yea and verily, but:
>All standard voltmeters, ammeters, and wattmeters are accurate
>only with sinusoidal currents
Depends on the definition of 'standard'. I consider hot wire
to be one of the 'standard meters'. If 'standard' is defined
as 'd'arsonval moving coil' (which is the MOST COMMON meter),
i concur.
>and TC currents are not sinusoidal.
Yeah verily.
>Note that all wattmeters are instantaneous.
WHICH 'all wattmeters'?
for 'classic four wire 'true' wattmeters' moreso than might
appear, but with the iron cores and the voltage coil,
especially, having many turns, they get squirelly up above
the mid audio range.
Modern electronic wattmeters, as noted, are likely better, but
STILL have a roll off somewhere.
>Hot wire ammeters are frequency sensitive because of the wire motion.
Two sorts of 'frequency sensitivity'. Properly constructed
hot wire techniques are usable up to RF, and were so used in the
past. The WON'T track 'instantaneous' changes, of course, they
won't indicate peak currents, but for currents of any frequency
within the design range they will do real well for slowish
changing currents..
(I have a Boonton (?) Model 80 Signal generator, state of the
art for its time, the calibration is set by hot-wire
techniques up to the 100s MHz region)
regards
dwp