Bimetallic Spiral Thermometer

bimetal spiral components

active

Mg

Al

Ag

Cu

passive

Ti

Fe

Ni

Au

strip thickness

0.2

outside temperature (°C)

20

auto-calibrate

This Demonstration simulates a classical bimetallic spiral thermometer (dial or coil thermometer).

An Archimedes's spiral made of a coiled bimetal strip gives a deflection proportional to the surrounding temperature and can serve as a thermometer.

The angular deflection of a bimetal spiral of length

L

and strip thickness

s

is given by

ϕ=(

α

1

-

α

2

)(T-

T

0

)L/s

, where

α

1

and

α

2

are the coefficients of linear expansion of the component materials used.