The common instrument used to obtain dew point and relative humidity is a psychrometer, which consists of two liquid-in-glass thermometers mounted side by side and attached to a piece of metal that has either a handle or chain at one end. The thermometers are exactly alike except that one has a piece of cloth (wick) covering the bulb. The wick-covered thermometer—called the wet bulb—is dipped in clean water, whereas the other thermometer is kept dry.
PRINCIPLES OF PSYCHROMETER
The Psychrometer is a hygrometer which measures humidity, dew point and temperature simultaneously by measurement of dry-bulb temperature and wet-bulb temperature.
In extreme high temperature, low temperature, low humidity, and low pressure, an error becomes large by the object for the measurement in general temperature and moisture environment.
Consisting of two thermometers, one side is a portion which makes a ball part always become wet with water and which is called a wet bulb. A wet bulb shows a temperature usually lower than another thermometer (dry bulb), in order that water may take evaporation heat by evaporation in a ball part. However, since a wet bulb is covered in the layer of thin ice when temperature is the freezing point, a temperature higher than a dry bulb may be shown.
Readings from dry and wet bulb will be compared and by using the specific table of data, humidity and dewpoint information can be obtained.
RELATIVE HUMIDITY CONVERSION TABLE
LOCATION ON THE VESSEL (PORT AND STARBOARD BRIDGE WING)
