Gas/Liquid Expansion Thermometer

A gas expansion thermometer is made of a cylindrical bulb filled with inert gas & uses the volume expansion of gases at temperature changes. Gas pressure changes inside the bulb due to temperature changes, are sensed by a special helicoil bourdon tube, which, connected to an amplifying device will give the pointer, movement proportional to the temperature.

The physical properties used will enable linear readings on the dial from the origin to full scale. When the reading is remote from the sensing point, a capillary is then used for transmission between the bulb and the thermometer head. Capillary armoring is common practice in industrial environments.