|MadSci Network: Engineering| Most thermometers depend on the
differential thermal expansion rates of materials to measure
temperatures. That is, we all know that materials expand in heat
and contract in the cold; what's less obvious is that different
materials do so at different rates. The rate is called
"coefficient of thermal expansion". I describe three different
designs below that reflect this principle and classic
thermometer designs. My recommendation is to go with design #3
as being the simplest in concept and construction. Thermometer
#1 -------------- The difference in expansion rates of different
metals is the principle is used in mechanical dial thermometers.
Consider two long strips of dissimilar metals are welded
together along their lengths. As the temperature increases, one
of the metal strips want to expand more than the other, so the
assembly bends towards the side that isn't expanding as fast. In
a dial thermometer, the bimetal strip is coiled into a spring
that expands as the temperature r