A hygrometer is an instrument used to measure relative humidity. A simple hygrometer has two thermometers mounted in a frame, with one measuring the air temperature and the other covered in wet cotton to measure the wet-bulb temperature as water evaporates. To use a whirling hygrometer, the user checks that it is fully prepared, takes temperature readings after rotating it for one minute at 200 rpm, then uses a formula involving the dry-bulb and wet-bulb temperatures and the dry-bulb temperature to calculate the relative humidity.

1. What is Hygrometer?
It is an instrument to determine the relative humidity of
air means percent-age of moisture in the air.
Construction
A simple example of Hygrometer is dry and wet bulb
Hygrometer. it has two thermometer which are monted
in suitable frame. one thermometer is used to measure
the actual temprature of the surrounding and other is
thermometer bolb is coverd with wet cotton/cloth dips in
small bottle filled with water. Costa evaporation of
Written by:-Sudipto Ch

2. Process of use Whirling
Hygrometer
1. Check the water in the
bottle and examiner all part.
2.Insure the temprature in the
thermometer
3. Take it into hand and start
rotating it with 200 r.p.m. for
1 minute.
4 Note down the dry and wet
bulb temparature.
Written by:-Sudipto Cha

3. Calculate the Reative humidity using following
formula
Relative Humidity = 100-C X (D.B.T.-
W.B.T.)
Take C = 7 if the D.B.T. is more than 25 Degree
celcious
C = 8 if the D.B.T. is bet 20 to 25 Degree celcious
C = 9 if the D.B.T is less than 20 Degree celcious
Written by:-Sudipto Ch