A psychrometer is a device which is used to measure the relative humidity at a given location or place. It is also referred to as the wet and dry bulb thermometer and is important in both laboratories and geological stations. It contains two thermometers which are similar in nature and is used to calculate the temperature in different environments. The dry bulb is directly exposed to the air while the wet bulb is wrapped in a muslin cloth and immersed in water. This wet bulb is removed from the water and allowed to cool by the evaporation of the water in the muslin cloth. The evaporation phenomenon is essential as it helps the data analyst to get an idea about the intensity of humidity. If the atmosphere is dry, the wet bulb will evaporate at a quicker rate. These values help in the calculation of the humidity. The value of the temperature is noted and the difference between the two readings helps in calculation of the humidity.
The humidity is inversely proportional to the difference in temperature of the two bulbs. Hence a higher difference indicates relatively low humidity while a low difference indicates high humidity in a particular area. The psychrometer is usually available in two variants:
Sling psychrometer: In this device, the bulb is whirled around and this helps in fastening the process of evaporation. The two bulbs are attached on a chain so as to provide a firm and steady support.
Ventilated psychrometer: In this device, air is blown into the bulbs with force.
Nowadays meteorologists make use of digital psychrometers as they are extremely accurate in their reading and do not involve hard work. Each digital psychrometer contains a temperature as well as a humidity meter which includes a wet bulb and dew points measurement as a built in default part. This psychrometer makes a quick and accurate assessment of the air moisture and hence helps in the correct prediction of values. They were designed in view to allow the measurements of wet bulbs without the slinging mechanism. The basic method followed is the calculation of the difference between air temperature and the probe wet bulb temperature using the temperature probe and the dew point value.
Making a psychrometer is a pretty simple process and can be carried out at home as well as in educational institutions to help students to get familiar with the calculation process. It requires 2 thermometers, a tape, wet gauze, a fan and a table for support. The first step is to tape the thermometers to the table so as to align them correctly. Next with the help of a rubber band we tie the wet piece of gauze to the liquid part of any one of the two thermometers. Once this is set up we place a fan in front of the thermometer and allow for the evaporation process to begin. We note the temperatures in each of the thermometers and calculate the relative humidity.