On Mon, 10 Dec 2001, Roman Black wrote:

> Peter L. Peres wrote:
> >
> > > One really cheap method is to use a 5w resistor,
> > > the white ceramic wire-wound type.
> >
> > Hm. there usually have 300 to 500ppm/deg temperature coefficient. This is
> > not so good. But there is an even cheaper method I've used (and still
> > use).  Use a tiny signal lamp rated maybe 30mA and 24V. This is around 800
> > Ohms when lit. When cold it is typically 1/2 to 1/10 of that. Use as a
> > RTD. It is good to almost 700C when the glass softens. I usually hold them
> > above a mild gas flame in tweezers until the bulb is drawn by the vacuum
> > and contacts the filament (on all sides). This reduces the time constant.
> > Use twiddled or compression connections or point weld. Solder won't work!
>
>
> Cool! An excellent idea, and with the interesting
> "glass-blower" approach is very interesting. So you
> modify the bulb to become a special purpose temp
> sensor?
> Does it matter if the bulb vacuum fails?
>
  of course ! The wolfram filament is covering with
oxide at high temperature and the resistance is changing
The method is good but have a little non-linear response.
Checked with small bulb ( those used inside an
electronic hand clock ). Another problem is aging;
But is a nice trick !
Vasile

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