TM 5-3610-252-14
CHAPTER 4
MASON-TYPE PSYCHROMETER
Section I INTRODUCTION
4-1. GENERAL INFORMATION.
4-1.1 Scope.
a.
Model Number and Equipment Name.
Model 314 Mason-Type Psychrometer.
b. Purpose of Equipment.
To measure wet and dry bulb temperatures from 20° to
120°F (-6.6° to 48.8°C), for determination of relative humidity.
4-2. EQUIPMENT DESCRIPTION,
4-2.1
a.
b.
4-2.2
Equipment Characteristics, Capabilities, and Features.
Direct reading.
Wall-mounted.
Equipment Data.
Dimensions
Length
9 in. (22.8 cm)
Width
4 in. (10.1 cm)
4-3. TECHNICAL PRINCIPLES OF OPERATION.
a.
The mason-type psychrometer is an instrument consisting of two thermometers,
used in the measurement of the moisture content (humidity) of air or other gases.
The bulb of one of the thermometers is covered by a thin piece of muslin cloth
(wick) wetted uniformly with distilled water.
The temperatures of both the bulb and
the air contacting the bulb are lowered by evaporation which takes place when
unsaturated air moves past the wetted bulb.
An equilibrium temperature, called the
wet-bulb temperature, will be reached; it closely approaches the lowest temperature
to which air can be cooled by evaporation of water into that air.
b. The water vapor content of the air surrounding the wet bulb can then be
determined by calculating the difference between the wet bulb temperature and the
dry bulb temperature.
The final determination is known as relative humidity, or the
amount of moisture in the air as compared with the maximum amount that the air could
contain at the same temperature.
Relative humidity is expressed as a percentage.
Where the dry bulb and wet bulb temperatures are the same, the atmosphere is
saturated.
4-1
