Figure 2-17.—A typical electric psychrometer. We have just covered several types of simple thermometers. Most frequently, the thermometers used by Aerographer’s Mates are found in psychrometers. Q11. Q12. Q13. Q14. Q15. REVIEW  QUESTIONS What are the two primary liquids found in thermometers? Where can you find detailed instructions for use and care of the different types of thermometers? How should the temperature be read from a liquid-in-glass thermometer? How  often  should  the  wick  on  a  wet-bulb thermometer be changed aboard ship? What instruction outlines procedures to be followed in the event of a mercury spill? PSYCHROMETERS LEARNING   OBJECTIVES: Define psychrometer. Explain the care and use of the electric, sling, and rotor psychrometers. A psychrometer is any device that contains both a dry-bulb and a wet-bulb thermometer used to measure ambient air temperature and wet-bulb air temperature. Currently   there   are   three   different   types   of psychrometers used by the Navy and Marine Corps: the electric psychrometer, the sling psychrometer, and the rotor psychrometer. ELECTRIC  PSYCHROMETER Electric psychrometers are used aboard some ships as the primary air temperature/wet-bulb temperature- measuring device. They are kept on hand at all shore observation  sites  as  a  backup  for  automatic  air temperature and dew-point sensors. There are several slightly different models of electric psychrometers in use: the ML-45O/UM and the ML-450(A)/UM through the  ML-45O(D)/UM  models,  and  the  "Type  III"  electric psychrometer. Figure 2-17 shows a typical electric psychrometer. All models contain a dry- and a wet-bulb thermometer,  a  small,  battery-operated  electric  fan, several  batteries,  thermometer  illumination  lights,  and  a small distilled-water bottle. Electric  psychrometers  should  be  allowed  to acclimatize to the ambient conditions if kept inside an office space, especially during extremely cold or hot weather. When the outside air temperature is cooler than 50°F or warmer than 85°F, allow the psychrometer to sit in a sheltered outside area 5 to 10 minutes before using. When the air temperature is below freezing, wet the wick and allow the psychrometer to sit 15 minutes before using, to allow the wick to freeze. To  avoid  acclimatization  time,  many  shipboard observers store the psychrometer outside in a sheltered location.  You  must  take  care  to  ensure  that  the psychrometer is held securely in the storage location to prevent breakage from the ship’s motions. Ashore, the electric psychrometers are usually stored outside in the instrument shelter. To use the electric psychrometer properly, wet the muslin wick with a few drops of distilled water from the bottle. Then, stand on the windward side of the ship or building with the air intake pointed toward the wind, turn the fan motor on, and hold the psychrometer at arm’s length. The scale lights should be turned on only when you read the temperatures. After 60 seconds, read the wet-bulb temperature at lo-second intervals until the  temperature  reads  the  same  for  two  consecutive readings. Record   both   the   wet-   and   dry-bulb temperatures to the nearest 1/10 degree. Then, turn the fan motor off. When  issued,  each  electric  psychrometer  is supplied with a use, care, and maintenance handbook. Routine  care  and  maintenance  of  the  electric psychrometer include changing the wet-bulb wick, keeping the psychrometer clean and dry, and changing the batteries and light bulbs. Cleaning and lubrication of the electric motor are also required. For more 2-12