From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: Quickie Thermal Probe
References: <3DF8FDBE.34F2@Spam.Bots> <email@example.com> <3DF93BF0.2EC3@Spam.Bots>
Date: Fri, 13 Dec 2002 02:03:00 GMT
NNTP-Posting-Date: Thu, 12 Dec 2002 18:03:00 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Mike Monett wrote:
> John Larkin wrote:
> > Mike,
> > transistors should work fine, but personally I wouldn't literally use
> > a diffamp; I'd rather each transistor be privately biased at a
> > constant current, which would avoid thermal runaway issues. You could
> > use, essentially, two emitter followers, bases connected, and use an
> > opamp to nab the differential emitter voltages.
> > Sure, a SOT-23 has a high theta j-a (like, 350 k/w) and a shorter
> > thermal time constant. I'd go for 100C or so idle temperature and get
> > lots of signal.
> > I did a thing like this once. We took it to the park and hung it way
> > out a car window to calibrate it.
> > John
> Thanks John,
> I can see it now - one to drive, one to hold it out the window, and one
> to record the speedo and meter readings. And onlookers shaking their
> heads in amazement!
> Your approach sounds good, and probably worked very well. I'm thinking of
> a much smaller temperature rise in the sense transistor - perhaps several
> degrees above ambient. Hopefully this will allow it to sense small
> changes in temperature as well as air currents.
> I'm not actually trying to measure wind velocity. The problem is mold
> spores coming up from the basement. I have carefully sealed all the floor
> trim and other cracks in the appartment, shut off the heating system and
> sealed the vents, sealed the entry holes for the pipes in the kitchen and
> bathroom, and sealed the light fixtures and wall switches. So there's no
> great rush of air, just a constant seepage. This allows spores to enter
> the appartment that make me very ill.
> I felt some suspected areas with my finger but could not feel anything.
> There are other places too difficult to reach, which is why I'm looking
> for a sensitive probe. A diffamp looks promising, and from your
> description the SOT-23 seems a bit better than a TO-92.
I thought that once one had mold spores, that it was essentially
impossible to get rid of them; only possible to greatly delay their
There is an anti-mold additive for paints, so that one can re-paint
I had to do that once and the result was very effective for the 5
years i was in that particular house.
I also understand that there is a possibility of serious reprocussions
when one drastically impeads airflow (replacement of air) in a building;
it can get "sick" (and the finding and fixing near impossible).
So it may be a good idea to investigate these issues and learn from
the majority wisdom.