The voltage stabiliser works on the same principle as the gauge i.e. a
heating coil wound round a bi-metal strip. *Any* heat will cause the strip
to bend, no matter whether it is from the heating coil or ambient, so the
gauge will display the effects of both heat sources. Because the stabiliser
is the same in high ambient temperature conditions it will require less heat
from the heating coil to move the bi-metal strip to break the contact than
in low ambient conditions so will break sooner. Once broken the bimetal
strip will cool more slowly in high ambient conditions than low, taking
longer to close the contact. The stabilising effect works by varying the
proportion of time it is outputting a voltage to the gauges compared to when
it is not, i.e. the 'ratio' or 'dwell' of a square wave. The main purpose
is to counteract changing system voltage which could be anywhere between the
low twelves to the high fouteens. A low voltage will cause the heating coil
to take longer to open compared to a high voltage, but the cooling time i.e.
time to close again will be about the same (for a given ambient). So a low
system voltage results in a higher proportion of voltage 'on' time to
voltage 'off' time compared to a high system voltage, and the *average*
heating effect at the gauge is about the same (for a given sensor
resistance). By contrast because a high ambient will result in a longer
cooling time this results in a lower proportion of voltage 'on' time to
'off' time (for a given system voltage), the average heating effect at the
gauge is lower, counteracting the ambient heating effect.
A simple voltage regulator is designed to give a constant voltage output
with changes in supply voltage *and* ambient temperature. I'm sure it is
possible to build an electronic system that outputs a similarly lower
voltage at higher ambients, but it would be an awful lot of pfaffing about.
PaulH.
----- Original Message -----
> As the ambient gets higher so the bi-metal warms up - but it
> will still cut off at the same temp thus still providing the square wave
> just as before.
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