GM temp sensors

[Tom Sharpe]

now that you know the shape of the curve, is there a similar one on the
motorola sensor data sheets? more work, but we might find out what the sensor
reaally is!!  TWS

Richard Wakeling wrote:

> Hi Frank and group,
>
> > Does anyone have the resistance values of the GM air/coolant sensor
> > at temps over 212 deg F. Have values at lower temps from GM Fuel Inj
> > Diag manual and other sources but those start at -40C/F and go to 212F
> > and go no farther. Am trying to develop a lookup table for my datalogger.
> > Any help greatly appreciated.
>
> The resistance values versus the temperature on both sensor are not
> linear to my knowledge. The table does not represent a straight line
> with regards to voltage. As for lookup tables, you could of course do
> the obvious and actually heat up the sensors in boiling water or
> something (of course only get it to about 95 degrees celsius), and
> measure the voltage. However, if you are using datalogging devices such
> as Diacom, you can always manually change the voltage, emulating a
> sensor, with a variable resistor, then read back the temperature on
> Diacom.
>  The GM data stream sometimes puts out the sensor as a reading of
> temperature (i.e. a single byte is dedicated to the temperature, and
> another to the voltage). I know that this however does not appear on the
> Sunbird data stream and I had to create my own lookup table. Once I
> obtained the voltage versus temperature, I did plot the result in excel
> but had to use a best line of fit, with a polynomial of degree 6! This
> of course was the best resolution possible. The result however still was
> a bit out, with some readings giving about 1.5 degrees celsius out
> (Australia here), however the overall map was plotted correctly. I
> believe using a lookup table would have to be more accurate however this
> uses up a reasonable amount of CPU time, depending on your aim.
>
> I don't really have the above problem in OZ though, coz the datastream
> in Oz puts out both the bytes dedicated to voltage and temperature. Hope
> this helps you out.
>
> Andrew Wakeling
> kojab at ar.com.au