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Measurements using field probe
-----Original Message-----
From: Jim Lux <James.P.Lux-at-jpl.nasa.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Date: Wednesday, July 01, 1998 1:58 PM
Subject: Re: Measurements using field probe
Tesla List wrote:
>
> ----------
> From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
> Sent: Tuesday, June 30, 1998 7:12 AM
> To: Tesla List
> Subject: Re: Measurements using field probe
>
> Tesla List wrote:
> >
> > ----------
> > From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
> > Sent: Monday, June 29, 1998 8:08 AM
> > To: Tesla List
> > Subject: Re: Measurements using field probe
> >
> > to: Bert
> >
> > It would not be reasonable to assume the 144 Ohm resistance for the 420
BPS
> > of operation. This value would only be true for the first few firings
of
> > the cap as the "hot" resistance of the bulb is considerably less than
its
> > initial "cold" measured DC resistance. After a few seconds this value
> > would be lower.
> >
> > DR.RESONANCE-at-next-wave-dot-net
> >
> > ----------
> <SNIP>
>
> D.C.,
>
> Actually, it would be closer to 13 ohms for the first few firings when
> the filament was cold... it rises to 144 ohms only at full operating
> temperature. A 10:1 resistance change is a bit non-linear for sure. I
> wonder if a carbon-filament lamp would have less of a resistnace swing?
Since carbon has a negative temperature coefficient, I would expect the
resistance of a carbon filament lamp to go down as it gets hot (seems to
be a recipe for thermal runaway). Manganese has the lowest coefficient
in my table: .00001 compared to .00380 for Copper. Constantan is also
quite low: .00003 (probably why it is named "constant"). Manganin is
also known to have a very low TCR (probably because it has manganese in
it?)