TM 5-3610-285-14
10-2.2 Equipment Data.
a.
Refrigerator. Single Door, 10.6 cu ft capacity, 120 V, 60 Hz power.
b.
Darkroom Safelight. 120 V, 60 Hz with filter.
c.
Contact Printing Lamp and Timer/Power Supply Control Box. 120 V, 60 Hz for
control box, 20 V 100 W lamp.
d.
Mason-Type Psychrometer. Is water activated, 9 in. (22.8 cm) in length and 4 in. (10.1 cm) wide.
e.
Vacuum Cleaner. 115 V, 60 Hz. Packed in storage box containing hose, various vacuum and blowing
attachments, liquid spray attachments, and motor repair kit containing motor bearings and brushes.
10-3. TECHNICAL PRINCIPLES OF OPERATION . Principles of operation are combined with operator's controls and
indicators, with exception of the Mason-Type Psychrometer.
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.
10-2
