The hygrothermograph senses humidity using a bundle of human hair that has been specially treated for the purpose. As the humidity in the atmosphere fluctuates, the hair expands or contracts. The movement is transferred mechanically to the lower pen arm, which moves up and down to record the humidity.

What is principle of thermo Hygrograph?

A thermo-hygrograph or hygrothermograph is a chart recorder that measures and records both temperature and humidity (or dew point). ... The pen is at the end of a lever that is controlled by a bi-metal strip of temperature-sensitive metal which bends as the temperature changes.

What is the function of hygrograph?

Thermographs and hygrographs are used for registration of air temperature respective of relative humidity. The sensor of the thermograph is a U-shape bimetal of high specific deflection. It reacts with a low response time to temperature changes.