December 17, 2018


Sling Psychrometer. Relative humidity can be measured by an instrument called a hygrometer. The simplest hygrometer – a sling psychrometer – consists of two. The Sling Psychrometer accurately determines percent relative humidity without the necessity of consulting complex tables. The Sling Psychrometer contains a. 24 Apr A sling psychrometer is an instrument that measures the relative humidity and dew point in an area. A sling psychrometer has two.

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Modern electronic devices use temperature of condensation the dew pointor changes in electrical capacitance or resistance to measure humidity differences. Of the several different types of hygrometers available for use, the sling psychrometer is the simplest, both eling terms of design and ease-of-use. If the surrounding air is dry, more moisture evaporates from the wick, cooling the wet-bulb thermometer more so there is a greater difference between the temperatures of the two thermometers.

A psychrometer, or wet-and-dry-bulb thermometer, consists of two thermometers, one that is dry and one that is kept moist with distilled water on a sock psychrometef wick.

Using a Sling Psychrometer to Measure Relative Humidity |

Basically you have to ensure that both, the thermometers on the device are displaying the same initial reading, so that the measurement commences from the same starting point. Hygrometers must be calibrated in air, which is a much less effective heat transfer medium than is water, and many types are subject to drift [8] so need regular recalibration. The instrument can be made more sensitive by removing oils from the hair, such as by first soaking the hair in diethyl ether.


Wrap it around the bulb of one of the thermometers. Attach the thermometers to a narrow, thin board with wire or strong tape. Relative humidity can be measured by an instrument called a hygrometer. This method avoids many of the pitfalls of the previous chilled-mirrors and is capable of operating drift free.

How to Read a Sling Psychrometer

Relative humidity is computed psychrometet the ambient temperature as shown by the dry-bulb thermometer and the difference in temperatures as shown by the wet-bulb and dry-bulb thermometers. Find paychrometer relative humidity using the bottom chart from the Resource listed below.

This is known as the dry-bulb thermometer. In this arrangement, a fan draws outside air past 1 a thermometer to measure the ambient dry-bulb temperature, 2 the heating element, 3 a second thermometer to measure the dry-bulb temperature of the heated air, then finally 4 a wet-bulb thermometer.

Taking the difference between these two values, one can obtain the exact drop in temperature. If they register different temperatures it will give you inaccurate results when computing humidity.

Towards the end of the 19th century, German meteorologist and physician Adolph Richard Assmann modified the design, and introduced a type of wet-dry bulb psychrometer with improved accuracy. Retrieved July 21, It is used to sling the device around in circular motions.

Other techniques were applied using mass to measure humidity, such as when the air was dry, the bar of charcoal would be light, while when the air was humid, the bar of charcoal would be heavy. If the surrounding air is relatively dry, more moisture will evaporate into it, and as a result, the measured drop in temperature will be greater. Various researchers [15] have investigated the use of saturated salt solutions for calibrating hygrometers. Lab Safety Rules for Kids.


The maximum amount of water vapor that can be held in a given volume of air saturation varies greatly by temperature; cold air can hold less mass of water per unit volume than hot air. Retrieved February 3, It can be purchased from the market or even built at home itself by using two commercially available thermometers.


Corina Fiore is a writer and photographer living in suburban Philadelphia. Who Invented the Battery. You can repeat the above procedure a few times and take the average of the results, to obtain a more accurate humidity value.

At the same time, the dry-bulb thermometer provides the original reference temperature reading. Slushy mixtures of certain pure salts and distilled water have the property that they maintain an approximately constant humidity in a closed container.

It has a simple design, and is accurate enough to be used for predicting weather patterns. This device, which later came to be known as Assmann’s psychrometer, worked on the same principle as the sling psychrometer, but instead of needing to be swung around, it used a spring-operated fan to generate the required air flow. When the air temperature is below freezing, however, the wet-bulb is covered with a thin coating of ice and may be warmer than the dry bulb.

In the following sections, we shall take a closer look at the sling psychrometer, and study its working. By using this site, you agree to the Terms of Use and Privacy Policy. However, a conventional hygrometer is unable to measure properly above the frost point, and the only way to go around this fundamental problem is to use a heated humidity probe.