Description

 Thermo-Hygrograph:

Thermo-hygrograph With Daily Chart

The Thermo-hygrograph is designed for measuring and
recording atmospheric Temperature & Humidity as a function of time on
recording chart. The Thermo-hygrograph uses simple mechanisms for measuring
both temperature & humidity. Measurements are recorded onto a rotating paper
chart. A rotating drum is driven  by  a  precision 
electronic Quartz clock. The chart paper used on the drum recorder has  two separate sections, an upper section for
temperature and a lower section for humidity. Both sections have the zero or
low-scale at the bottom edge of  the  scale 
and  the  full-scale 
or high-scale at the upper edge. A curved,   bi-metal element bends and straightens
as  the 
air  temperature around it
changes. The bending of the curved
element moves the temperature pen arm and results in the recording on the chart
paper. Relative humidity measurements are made with a human hair sensing
element. Changes in the moisture content of the air causes the length of the
hair to change. The hair is attached firmly to the frame of the
thermo-hygrograph so that the expansion and contraction of the hair can be
translated into the movement of the pen arm.