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Re: Hot Wire Metering

Subject:  Re: Hot Wire Metering
  Date:  Fri, 30 May 1997 19:40:40 +0000
  From:  "John H. Couture" <couturejh-at-worldnet.att-dot-net>
    To:  Tesla List <tesla-at-pupman-dot-com>


At 02:14 PM 5/30/97 +0000, you wrote:
>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
>
>-----------------------------------------------------------

   DWP -

  Thanks for the comments. I always wonder if I am overlooking the some
of
the many possibilities when it comes to Tesla coil engineering. One
method
to measure current I did not mention is the use of a lamp. I found the
lamp
method is much easier to build and cheaper than the hot wire meter.  

  Do you also have a Boonton 265 Q Meter?  If you have, I have the rare
Q
Factor article from the Boonton 'Notebook' spring '54. If you are
interested
I will send a copy for a SASE.

  John Couture