> 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

Yes. The small bulbs all have a vacuum in them (a pretty good one - 1.E-3
or better - unlike normal bulbs which are backfilled with Nitrogen or
Argon). If you collapse the bulb carefully from all sides using a gas
flame then the glass will touch the filament on all sides and there will
be no 'air' left in the bulb. The filament will be protected by the glass
as before. Aging is not a problem but a bakeout would be a good idea
(maybe 300C for 2 hours followed by very slow cooldown - another 2 hours
probably) to anneal the glass.

The oldest such sensor I have made (7 years old now) has unmeasurable
resistance deviation since then (<0.1Ohms from 100OHms which is 0.1%, and
this is due to the limits of my measurement probably).  This is to be
expected with glass cased or molded devices (which are the best aging-wise
afaik). Just use good quality signal lamps. The 7 year old one was by
Tungsram.

I tried to do hot wire anemometry (low speed) with a collapsed bulb but it
does not work right.

Peter

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