Hygrometer: What is it, how does it work, its types, and applications

hygrometer

You must have experienced either too much moisture in your room or too little than it should optimally be, right? Not having optimal moisture in your room or surrounding is not favorable in any sense. For example, too much moisture will leave you to sweat more while too little of it will make your skin dry. Both these can easily be experienced in the rainy and winter season respectively. Also, not having enough humidity in the air is a major cause of difficulty in breathing if you’re in any confined area.

As a thumb rule, an average of 30-50% humidity is a must from your comfort and health point of view, according to this. This means that the air can retain 30-50% of the maximum percentage of moisture it can contain. Yes, I know no one can see how much water vapor is present in the air but you can measure it by yourself using a portable device called a hygrometer. If this sounds interesting to you, this article will surely surprise you. So, read on.

So, what is a hygrometer?

A hygrometer is a portable hand-held weather instrument that measures the amount of water vapor/moisture/humidity in the air, soil, or any confined place. Though today you can see various upgraded models of hygrometers in the market, the first-ever design of the same was given by Leonardo da Vinci in the 1400s. Below are its image and a brief idea behind it.

As you can see, Leonardo da Vinci created a simple yet clever design wherein two absorbent and non-absorbent materials were fixed around a gauge. Now, as the humidity in the air increases, due to its absorbing power, the absorbent material will get saturated with moisture and become heavy. This difference in weight of the absorbent and non-absorbent material was then used to determine the relative humidity in the air.

The above design was simple, clever, yet needed improvements for better accuracy as provided by Horace Bénédict de Saussure, a physicist and a geologist from Switzerland through his design of a hygrometer.

In this model of hygrometer, he suspended the hair strand on the device at a certain tension. Now, as the moisture level in the air around the hair strand would vary, it’d either contract or expand. While doing so, the hair strand will move across the graduated scale to determine the humidity in the air.

Since then, the hygrometer has undergone several studies and subsequent innovations that resulted in today’s most accurate and easy-to-use hygrometer. Read on to know how it works.

How does a hygrometer work?

There are multiple types of hygrometers (I’ll come to this later) out of which the most commonly used is the psychrometers.

A psychrometer uses two thermometers:

● A dry thermometer that measures the temperature by being exposed to the air.
● A wet thermometer that measures the temperature by being dipped in water.

The temperature difference of these two thermometers is what you assume to be the relative humidity in the air.

Since dry air absorbs more moisture from the air than wet air, you won’t find much temperature change in the wet thermometer. And it’s the basic principle of the wet thermometer i.e. lesser the change in the wet thermometer temperature, the more humid the air will be, and vice-versa.

With advancements, you today have digital psychrometers that can produce the results in merely 20-30 minutes and besides humidity in the air, they can also measure the air temperature, surface temperature, and dew point.

Types of hygrometers

There are multiple types of hygrometers with a distinct way of working to let you measure just one thing i.e. humidity in the air. These are discussed below.

1. Electrical hygrometers

In electrical hygrometers, there are further two categories:

● Capacitive Hygrometer

In this, there are two metal plates with air between them. As the humidity in this air varies and so does the plates’ static electric charge storage capacity. This variation helps in determining the amount of moisture present in the air.

● Resistive Hygrometer

In this, there are two metal plates with air between them. As the humidity in this air varies and so does the plates’ static electric charge storage capacity. This variation helps in determining the amount of moisture present in the air.

In this, a ceramic material is present that’s exposed to the air. As the water vapor condenses inside of it, the alterations in the humidity level result in the alterations in the resistance level. This measures the humidity levels in the air.

2.Psychrometers

As said above, a psychrometer is a special type of hygrometer with two thermometer bulbs: wet and dry. The temperature difference of these two thermometer bulbs is what you assume to be the relative humidity in the air.

3.Dew point hygrometers

A dew point hygrometer is the most precise hygrometer you’ll ever come across and is generally used when you need to identify and measure even the smallest amount of moisture in a gas, say for storage purposes. Due to this, these are slightly expensive.

4. Hair-tension hygrometers

Designed by Horace Bénédict de Saussure, a hair-tension hygrometer involves a hair strand suspended at a certain tension. As the moisture level in the air would vary, the hair strand would either contract or expand. While doing so, it’ll move across the graduated scale to determine the humidity in the air.

5. Metal-paper coil hygrometers

● Digital hygrometers

Digital hygrometers are the savvy versions of traditional hygrometers with an LCD screen. These are more portable and give quick readings of indoor and outdoor temperatures, plus the relative humidity (RH) digitally. There are two models of digital hygrometers: HTC-1 and HTC-2. There are some differences between these two like:

● The HTC-2 displays indoor and outdoor temperatures separately while HTC-1 may or may not display the same.
● The temperature range of HTC-1 hygrometers is usually -10-degree Celsius to +50-degree Celsius or 14-degree Fahrenheit to 122-degree Fahrenheit. While the temperature range of HTC-2 hygrometers is -10-degree Celsius to +70-degree Celsius or -58-degree Fahrenheit to +158-degree Fahrenheit.
● The relative humidity range of HTC-1 hygrometers is 10%-90% and the same of HTC-2 is 1%-100% (or 10%-99%).

So, these are some of the common types of hygrometers you can easily access.

Hygrometers usage & applications

If you think a hygrometer can merely be utilized for humidity measurements, you’re WRONG!!

While some devices are specific to humidity measurements, others can be used for a vast list of applications as listed below
.

● Measuring humidity in the indoors and outdoors,
● Predicting the weather,
● For determining the optimal conditions for storage houses and warehouses,
● Greenhouses,
● In wine cellars, etc.

Final words

A hygrometer isn’t a new concept and has been under study and innovation since the 1400s. It’s a simple, easy-to-use, and economical device one can use at different locations to determine the humidity levels there. This is because humidity plays a vital role as per the settings like storage areas, baby room, kitchen, offices, yoga room, etc. With this being said, there are likewise different types of hygrometers you can choose from which have distinct working principles but the same purpose of measuring HUMIDITY! So, what are you waiting for? Order yours, now!

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