A sling psychrometer is an instrument that measures the relative humidity and dew point in an area. A sling psychrometer has two thermometers: a wet bulb and a dry bulb. The wet bulb has a cotton wick on the bulb of the thermometer, which is moistened with water at room temperature. The dry bulb is simply a thermometer. Both are tied to an ankle with a screw so that the air can spin them. A sling psychrometer works on the principle that evaporation is a cooling process. The air dryer, the more the evaporation takes place out of the wet bulb, let the temperature drop on the thermometer.
• Wet the cotton wick with wet bulb thermometer water at room temperature.
• Make sure both thermometers are attached to the ankle and swing them around for a minute.
• When you have finished swinging the psychrometer, record the temperature of the dry thermometer and wet bulb. Note: The wet temperature is never warmer than the temperature of the dry thermometer. If the wet temperature reads hot that the thermometer is dry, then the water is too hot, or psychrometer is broken.
• Find the difference between damp temperature and dry bulb temperature. Record. For example, if the dry bulb temperature is 22 ° C and the wet temperature is 18 ° C, the difference between the two is 4 ° C.
• Find the dew point using the graph at the top of the resource below. Use the dry bulb temperature of the y-axis and the difference between the wet and dry bulb on the x-axis. The temperature where the two meet is the temperature of the dew point in ° C. The dew point temperature is the dew point of the air that begins to form.
• Find the relative humidity using the chart at the bottom of the resource below. Use the dry bulb temperature of the y-axis and the difference between the wet and dry bulb on the x-axis. The telephone number where the two meet in the table is the relative humidity expressed in percent.
A psychrometric chart is a handy tool that allows the reader to determine and calculate dry bulb, wet bulb, relative humidity, dew point temperature as well as other gas-vapor relationships with only limited information. This table helps people, who are mainly involved in heating, ventilation and air conditioning systems, to determine levels of human comfort based on changes in temperature and humidity.
Determine the temperature of the dry bulb at your location. This can be done by reading a simple thermometer at your location.
Determine the relative humidity at your location. This can be done by reading a hygrometer at your location, or by getting information from a local weather station.
Locate the temperature value measured in step 1 on the lower axis (X) of the psychrometric chart. Follow the line indicated by this value vertically until you reach the intersection line of the value you obtained from your hygrometer. Lines indicating relative humidity begin at the bottom left of the map and radiate to the upper right of the map, increasing in value of the bottom of the map upwards.
Follow the diagonal line from which the relative humidity and relative humidity lines intersect at the top left. When this line meets the left side of the graph indicates the temperature of the wet thermometer. This value can also be obtained by measurement using a sling psychrometer.
“Follow the line where the relative humidity and dry bulb temperature meet at the left edge of the map along the horizontal line to obtain the dew point temperature at your location as measured above. With these data, you can determine how humidity, dew point temperature, and wet bulb temperature will be affected by changes in dry bulb temperature and vice versa.”