temp gauge internals

[Brett Dikeman]

Your analysis of the meter is correct; the strip heats up as the
temperature sensor decreases in resistance when it gets hotter; the hotter
the sensor, the more current flow.  As the strip warms up, it
curls(bimetallic, one side expands faster than the other) and the needle
moves.

This is why, if the engine is hot, it still takes 15-30 seconds for the
gauge reading to climb up.

The same principle is used in common household thermostats for
heating/cooling.  Some even have an adjustable resistor that passes
current through the bimetallic strip to account for additional heating
that occurs in many systems(steam, forced hot water, etc.) because of the
heat capacity of the water still in the radiators.  It also helps
account for time it takes the metallic strip to react to changes in
ambient air temperature, or for the time it takes for the air near the
thermostat to warm up.


Brett

 On Sat, 30 Jun 2001, Konstantin Bogach wrote:

> Hi listers.
>
> I decided to forward back to the list the message I sent ealier under
> different subject because I suspect that many people found that thread
> not interesting and could just skip it.
>
> The reason I do that is I realy very curious how the gauge works. I
> would appreciate if someone comment on it.
>
> Thanks.
> Konstantin Bogach.
>
> -------- Original Message --------
> Subject: Re: HELP! Anybody who knows how gauges work!
> Date: Fri, 29 Jun 2001 01:35:54 -0400
> From: Konstantin Bogach <kbogach at home.com>
> Organization: Morgan Stanley Dean Witter & Co
> To: quattro at audifans.com
> References: <20010628124104.25133.qmail at web12101.mail.yahoo.com>
> <3B3B351F.35A2FC7 at home.com>
>
> I was inside the temp gauge.  Definitly somebody played with needle. And
> I
> know who it was - my 2 years old daughter.  I took her seconds before
> she lost
> interest. Nobody saw it.
> It is fixed now.. By the way I can explain what I saw just as
> bimetallicU-shaped strip with wound wire around one leg which servse as
> a
> heater, I think. But I never heard about such kind of gauge
> construction.
> Heater inside the gauge? Hmm.  From other hand I can not find any other
> physics inside the gauge.  If I am wrong  then I overestimated my
> knowledge of
> physics.  I would appreciate if someone prove it in this case.
>
> Speedo needle was overturn and not being able to take the needle off I
> just
> forced it in oposite direction and it rotated on the shaft. Now it
> starts on 0
> and goes all the way up.
>
> Sorry for panic posts.
>
> Konstantin Bogach.
>