VRMan said:
> A little off the topic, but who do I need to slap for making up these
> gauges? What kind of mathematical exponential curve did they use to create
> them? ie, check that temp gauge..my halfway point says 210, which isn't
> mathematically halfway between the lower and upper reading printed on it
> even tho the distance between the two looks the same.
Okay... remember you DID ask. :-)
Temperature sensors typically work by making them out of some material
with the property that its electrical resistance changes with temperature.
Then you feed a known voltage or current through it and watch how much it
drops.
Unfortunately, the relationship between temperature and resistance is not
linear. The ones I work with are quadratic, for example resistance in
Ohms might be equal to 100 + 0.3454 * T - 0.000054343 * T ^ 2 for T > 0C,
and 100 + 0.385 * T for T <= 0C. This is measuring air temperature, I'm
not sure if the sensor for coolant temp would be at all similar or not.
I'm sure there's lots of reference material on the web that could tell you
the exact equations for automotive applications.
Now, I do know that there are two coolant temp sensors. One has two wires
(signal and ground) and goes to the PCM, the other has one wire (signal;
it just uses chassis ground) and is used for the dash. Right away you can
guess that the dash sensor is going to be less accurate. I'll pretty much
guarantee that they don't go to the trouble of calculating the actual
temperature for the gauge in the dash. My guess is that it's just a
voltmeter that's set up to put the needle in about the middle for "normal"
temperatures, then they put some numbers on it to amuse people. It's
hardly a calibrated instrument.
In short, I wouldn't really trust the actual values it tells you. If you
need to know the real coolant temp, get a thermometer probe and figure out
a good place to take a reading.
-- Jason Bleazard http://www.bleazard.net Toronto, Ontario his: '95 Dakota Sport 4x4, 3.9 V6, 5spd, Reg. Cab, white hers: '01 Dakota Sport 4x4, 4.7 V8, Auto, Quad Cab, blackDidn't you read the disclaimer? http://www.they.com/disclaimer
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