Thermal Divider

If you mount the sensor in a bar that is picking up heat at one end, and
losing heat at the other - you sensor will read somewhere between the two
temperatures. But, if you don't know a lot about the heat transfer rates
at each end, you will not know how the temperature your sensor sees is
related to the temperature you want to measure.

That's exactly the point, Geoff. When I do a resistive divider, it is always
between two "hard" voltages, either a variable voltage and a reference
voltage or a variable voltage and ground. I know what the reference is and
can easily calculate the variable. The thermal reference is not quite so
trivial. It is a function of airflow, ambient temperature, and phase of the
moon.



Think of a series voltage divider with two known resistors in the middle
and an unknown resistor attached to each end. What does the votage
measured at the junction between the two known resistors tell you about
the source voltage?


Absolutely nothing. An equation in one unknown with two degrees of freedom
is insoluble. There are an infinite number of correct answers and an
infinite number of incorrect answers. HOWEVER, if you let me measure the
voltage ACROSS one of those known resistors and THEN the voltage at the
junction, I've got a fighting chance if you know what the bottom end
resistor is tied to.

Jim