Thermo Hygrograph

July 8th, 2014 by Acmas Leave a reply »

A Thermo Hygrograph is a scientific instrument which measures the Temperature and Humidity and plots it on a chart. It monitors the environmental changes. Thermo Hygrographs are used to produce a continuous record of the variation of both the Temperature and Relative Humidity of the atmosphere against time, by drawing colored traces on a chart.

Thermo Hygrograph is portable, accurate and easy to operate. Variations in Relative Humidity can affect many manufacturing processes, storage of raw materials, weights of items such as wool, paper, tobacco, confectionery, and computer operation, as well as being an important factor in human comfort. Since Temperature is often linked to changes in Relative Humidity, this instrument records both on a single chart.

Thermo Hygrograph requires ongoing maintenance to ensure that they are recording accurately and to ensure that the cylinder is rotating at the right rate. And Thermo Hygrograph also needs to be calibrated periodically.


Thermo Hygrpgraph works on the principle that organic materials expand and contract as the Relative Humidity changes. In this case, the organic material is Human Hair (it is need to be reconditioned).

The hairs are bundled together and stretched between a fixed pin and movable pin. The movable pin is attached to a series of levers, which amplify the movement of the hairs. A pen is attached to the end lever, and this pen plots the movement of the lever on a chart, which is mounted on a rotating cylinder. The rate of rotation can be altered, so that the Relative Humidity is plotted over a day, a week or a month.

It also has a Temperature Sensor which records the Temperature on same chart. The chart should be changed at the end of each recording period and the pen should be set on the correct line.


  • It measures the temperature and relative humidity of
  1.  Museums
  2.  Libraries
  3. Storage Areas
  • It gives the relationship between humidity and temperature.
  • The chart also shows when fluctuation occurred, so one can relate fluctuation to events in the area being monitored, e.g. the arrival of a bus load of tourists on a wet day.

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