Environment (other)

What Does a Hygrometer Measure?

German Portillo
By German Portillo. March 20, 2024
What Does a Hygrometer Measure?

Hygrometers are devices used to measure the relative humidity of air or solid materials. Many of us associate them with monitoring or predicting the weather, but these instruments are used in a variety of applications. Such applications include indoor climate monitoring, agriculture, meteorology and the food industry. There are several types of hygrometers, each with its own operating principle and application.

At thedailyECO, we ask what does a hygrometer measure? In addition to looking at the measurement readings it provides, we find out the different applications for its use depending on type and function.

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  1. What is a hygrometer?
  2. What does a hygrometer measure?
  3. How a hygrometer works
  4. Types of hygrometers

What is a hygrometer?

A hygrometer is a device used to measure humidity in the air or in solid materials. It works by measuring the amount of water vapor present in the air or a material. The readings of hygrometers are expressed as a percentage of the maximum possible amount of water vapor that the air or material could contain at a given temperature and air pressure.

Hygrometers can use a variety of methods to assert this measurement:

  • Capacitive humidity sensor: measures the electrical capacity of a water-sensitive material.
  • Resistive humidity sensor: measures the electrical resistance of a material that changes with humidity.
  • Synthetic hair humidity sensor: changes its length in response to changes in humidity.

Most modern hygrometers also include a thermometer to measure temperature. This is because the relative humidity of the air is closely related to temperature. By combining the humidity reading with the temperature reading, hygrometers can provide a more accurate relative humidity reading. If you would like to have one at home, you can use the link below to purchase your own:

What Does a Hygrometer Measure? - What is a hygrometer?

What does a hygrometer measure?

As explained above, hygrometers are used to measure humidity in both the air and in solid materials. While this is the basic function, this can be used for various applications. Hygrometers can be used indoors for homes and businesses, but they can also be important in the food industry, agriculture, brewing and even to help predict the weather.

Hygrometers can be used to measure humidity for protective purposes. For example, art galleries and museums can use them to protect their works from the damage moisture can cause. Equally, they are useful in the pharmaceutical industry to prevent sensitive compounds from being damaged by moisture in the air. With this in mind, we can look at some of the specific things hygrometers are used to measure:

  • They are commonly used in homes, offices and other indoor spaces to monitor and control relative air humidity. In agriculture, hygrometers are essential for measuring soil and air humidity in greenhouses and other agricultural facilities. Precise humidity control is essential to optimize crop growth and prevent diseases caused by excess or lack of humidity.
  • In the food industry, these devices are used to control humidity in food processing, storage and transportation. Maintaining adequate humidity levels is important to preserve the quality and safety of food products, as well as prevent the growth of pathogenic bacteria, fungi and mold.
  • Especially for research and development in various industries, hygrometers are used in laboratories to monitor humidity in growth chambers, incubators and other specialized equipment. Precision humidity control is essential to the success of many scientific experiments and processes. A good example of this is when medical testing is carried out in a lab where the humidity can affect the accuracy of the outcome
  • Hygrometers are important components in weather stations and weather forecasting devices. They help measure the relative humidity of the air, essential for understanding and predicting weather patterns and atmospheric conditions.
What Does a Hygrometer Measure? - What does a hygrometer measure?

How a hygrometer works

To learn how a hygrometer works, we must know its main components and what functions each of them performs:

  • Capacitive Humidity Sensor: one of the most common methods used in modern hygrometers is the capacitive humidity sensor. This sensor consists of two parallel plates, one of which is coated with a moisture-sensitive material such as a porous polymer. When air humidity changes, the sensitive material absorbs or releases water, altering the dielectric capacity of the sensor in the process. By measuring changes in electrical capacity between the plates, the hygrometer can determine the relative humidity of the air.
  • Resistive humidity sensor: this sensor uses a ceramic or polymer material that changes its electrical resistance in response to changes in humidity. When humidity increases, the material swells, increasing its electrical conductivity. By measuring the electrical resistance of the material, the hygrometer can calculate the relative humidity of the air.
  • Synthetic hair humidity sensor: although less common in modern devices, some hygrometers use a synthetic hair humidity sensor. These devices consist of a lock of human or animal hair chemically treated to make it sensitive to changes in humidity. When humidity increases, the hair expands. When humidity decreases, it contracts. A sensitive measuring mechanism records these changes and provides a relative humidity reading.

Regardless of the type of sensor used, many hygrometers also incorporate a thermometer to measure room temperature. This is important because the relative humidity of the air is intrinsically related to temperature. Therefore, combining humidity measurement with temperature measurement allows for more accurate relative humidity readings.

Learn about a natural way to control humidity indoors with our article on plants that absorb moisture.

What Does a Hygrometer Measure? - How a hygrometer works

Types of hygrometers

There are several types of hygrometers with different functions. Some of the main ones include:

  • Mechanical hygrometers: these are simple devices that use a moisture-sensitive material such as human or animal hair that expands or contracts in response to changes in humidity. These devices are typically connected to a gear system that amplifies the movement of the sensitive material, allowing relative humidity to be displayed on an analog scale.
  • Psychrometric hygrometers: these use evaporative cooling principles to measure the relative humidity of the air. They consist of two thermometers, one with a dry bulb and one with a wet bulb. They are exposed to the same air flow. By measuring the temperature difference between the two thermometers and consulting specific tables, the relative humidity of the air can be determined.
  • Shade hygrometers: these hygrometers are simple devices that consist of a thermometer wrapped in damp cheesecloth. Evaporation of water from the gauze will cool the thermometer and the temperature reading can be used to determine relative humidity using a correction table.
  • Capacitive hygrometers: use a capacitance sensor to measure relative humidity. These devices are common in commercial and home applications due to their accuracy and reliability. They often have a screen to provide a digital reading of the humidity and temperature.

Now that you know what a hygrometer measures and its types, you may want to check out our related article which explains the difference between temperature and heat.

If you want to read similar articles to What Does a Hygrometer Measure?, we recommend you visit our Environment (other) category.

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What Does a Hygrometer Measure?