This document summarizes instruments for measuring temperature and humidity. It describes how temperature is measured using thermometers calibrated to the Celsius, Fahrenheit, and Kelvin scales. Relative humidity is defined as the percentage of water vapor present compared to the maximum possible at a given temperature. Common instruments are described, including the instantaneous thermometer for single temperature readings, totalizer thermometer for minimum and maximum over time, and psychrometer using dry and wet bulb thermometers to calculate relative humidity by comparing the temperature drop from evaporation. The psychrometer consists of the two thermometers, a reservoir, and stocking to wet the wet bulb.

1. STUDY OF TEMPERATURE AND
HUMIDITY MONITORING INSTRUMENTS
Presenter:
Manish Kumar pal
ENT-07M-2017
Agriculture and Forestry university
Rampur, Chitwan
5th March,2019

2. Temperature
• It is a physical quantity expressing
hot and cold.
• It is measured with a thermometer
calibrated in one or
more temperature scales.
 Celsius scale (centigrade)
(denoted °C)
 Fahrenheit scale (denoted °F)
 Kelvin scale(denoted K)
Relative humidity
• It is the amount of water vapor (%)
present in the atmosphere compared
to total amount air it can hold at a
given temperature
• If relative humidity is 100% then
precipitation is occurring
5th March 2019

3. Temperature Measuring instruments
Instantaneous thermometer
Also called as Ordinary mercury-
In-Glass Thermometer.
Is used far instantaneous
determination of temperature .
Gives only maximum air
temperature at the time of reading.
Can be accurately recorded only
if the bulb of thermometer is
protected from sun.
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4. Temperature Measuring cont…
Totalizer thermometer
It is a special U-shaped
thermometer with maximum on
the left and minimum on the
right side mounted on a board.
Graduated both centigrade and
farenheight, that is highly
desirable for measuring the
temperature over a period of
time.
The maximum temperature is
reached during day and
minimum temperature during
the night.
5th March 2019

5. Relative Humidity measuring instruments
Psychrometer (dry and wet bulb thermometer)
It consists of two ordinary thermometers fixed to
a board.
The bulb of one is open to the air that records the
temperature under the dry condition
The bulb of other is wrapped with a piece of a
cotton wick for the purpose of wetting and
recording temperature under wet condition.
As the water from the wick evaporates, it cools
the bulb thus lowering the reading of the wet bulb
thermometer.
The rate of evaporation depends upon the dryness
of the air.
Therefore, the greater the fall in wet bulb
thermometer, the drier is the air.
A reference to conversion table about the fall in
temperature at any given atmospheric
temperature also gives the relative humidity.
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6. 6
Psychrometer Parts:
•Dry Bulb Thermometer
•Wet Bulb Thermometer
•Reservoir and Stocking
WETDRY
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7. Relative Humidity cont……
5th March 2019