Helix Bimetallic Thermometer Principle

This article is a continuation of my previous post on Bimetallic Thermometer

Principle of Helix Bimetallic Thermometer:

When a bimetallic helix fixed at one end and free at the other end is subjected to a temperature change, the free end of the bimetallic helix deflects proportional to the change in temperature. This deflection becomes a measure of the change in temperature.

Description of Helix Bimetallic Thermometer:

The main parts of a helix bimetallic thermometer are as follows:

1. A bimetallic helix which is fixed at one end to the body of the instrument and free at its other end.
2. To the free end of the bimetallic helix is attached a shaft.
3. One end of the shaft is mounted in friction less arrangement and its other end is connected to a pointer which sweeps over a temperature calibrated circular dial graduated in degrees of temperature.

Operation of Helix Bimetallic Thermometer:

When temperature of a medium is to be measured, the bimetallic thermometer is introduced into the medium for a length “L”

The bimetallic helix senses the temperature and expands resulting in a deflection at its free end.

This deflection at the free end of the bimetallic helix rotates the shaft connected to it. When the shaft rotates , the pointer attached to the shaft moves to a new position on the temperature calibrated dial indicating the measured temperature.