In a message dated 97-01-07 14:51:14 EST, Malcolm wrote:

> Thermocouples are typically used to measure high temperatures, like
>  exhaust gas temps.  a JK thermocouple sells typically for about $10-$20.
>  
>  Thermistors and regular silicon diodes are better at the temps your
talking
>  about.  You can even use a regular silicon transistor, and these all sell
>  for pennies.
>  
>  these all change resistance with temperature, and the standard PC game
port
>  has four time-based resistance measuring elements in it, perfect for this.

Thermocouples don't change resistance with temperature.  They work by the
principle that dissimilar metals, when placed in contact with eachother, will
create a small electrical voltage.  Thermocouples are made of such dissimilar
metals like Nickel-Chromium & Nickel-Aluminum (type K) or Iron &
Copper-Nickel (type J) and produce a voltage of 0mV (32defF) to 54.8mV
(2500degF) for a type K.  Thermocouples will measure temperatures over a very
wide range (like 32degF - 2300degF), but usually only have an accuracy of
around plus/minus 4degF.

RTDs (Resistance Temperature Detectors) on the other hand are a device that
(as their name applies) varies resistance with varying temperature. A 100 ohm
platinum RTD has 100 ohms resistance at 0degC and (less at lower temps) 138.5
ohms at 100degC, and 175.8 ohms at 200degC.  

If resistances in these ranges can be used as an input to game ports, it
looks like an inexpensive solution.  Although I don't know much about game
ports, I'd guess that the resistances they expect to measure are in the Mega
ohm range.  
Does someone know??

We (the company I work for & I) supply computerized systems for industrial
process control.  I could put together an industrial system to
comprehensively monitor a Vanagon for about $20,000 - $30,000.  Any takers??

Regards,
Jim Davis
87 GL Syncro
88 GL Wolfsburg