Bill Holden wrote:
>
> To List - the following comments were made to me by 'Tiger' Tom Ehrhart
>and.......<Clip>
Mu view: The gauge, which is basically a heater wrapped around a
bimetal strip, is in series with the temperature sensor, which is a
temperature sensitive resistor. About 10V average from the panel
voltage regulator is always across this series string. As the
temperature varies, the resistance of the sender varies, so the current
through both varies. The changing current causes the heater temperature
to change causing the bimetal strip to change shape and move the pointer
up or down. I'm just guessing but I'll bet the reisitance of the heater
in the gauge changes a bit, too, as it's temperature varies, though this
is probably minimal versus the change in sender resistance.
While the description of the experiment would do a fine job in of
determining the resistance of the sender, the description seems to break
down after this. The current through the string is not constant,
therefore the results of a constant current experiment do not apply.
What's the easiest way to check your gauge/sender calibration? With a
new or trustable thermostat, watch your Tiger warm up. The temp will go
up to where the thermostat opens, then stabilize around there
(temporarily, anyway). The reading on the gauge should then be
somewhere around your thermostat temperature. I have a 185F thermostat,
and mine stabilizes around 190-195 on the gauge. 5 or 10 degrees
difference? Big deal. It's unlikely that both the sender and
thermostat will go bad together in such a way that they always match, so
if it continues to stabilize at the same point, I'm happy. If it
doesn't, then I know something is wrong.
Stu
|