Thermometer and humidistats

A number of people have contributed to the development of the thermometer - Cornelis Drebbel, Robert Fludd, Galileo Galilei and Santorio Santorio. The word thermometer is derived from two Greek word fragments - "thermo" means "heat" and "meter" means "measure". Learn more at KlimaLex.

Further information about Thermo- & Hygrometer can be found at End of this page.

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Thermometers are instruments for measuring temperature or temperature gradients according to many different principles. You can measure the temperature of solids, liquids or gases. The thermometer consists of two key elements: the temperature sensor and a medium that allows the end user to transform physical changes into numerical values.

Types of thermometers

The following are some of the common types of thermo meters listed: Alcohol thermometer; Mercury thermometer made of glass; Beckmann differential thermometer; Mechanical bimetallic thermometer; Coulomb blockade thermometer; Galileo thermometer; Infrared thermometer; Liquid crystal thermometer; Quartz thermometer; Rectal thermometry; RTD; reversing thermometer.


The temperature measurement is performed by the thermometer using mercury, which expands when heated and contracts with a temperature drop. As a result, the length of the liquid column becomes longer or shorter depending on the temperature. Today, thermometers are calibrated in standard temperature units such as Celsius, Fahrenheit or Kelvin.


Thermo-meters are needed for numerous purposes from household to industry. In the kitchen, the temperature of food can be measured. Likewise, it helps in the fridge to maintain a set temperature. In a factory, the thermo-meter in the oven enables the stove to be switched on and off. It is therefore important to select the right thermometer type for the intended application.

The following is a list of other important thermometer applications: In motor or bearing monitoring; Air conditioning; Transport and vehicle samples; Surfaces for the preparation of food; to detect hidden problems; for measuring buildings for moisture and leaks; to detect energy losses and inadequate insulation, electrical faults and installation problems; in laboratories and storerooms.


What is a humidistat?

To understand how a hygrometer is used, you need to know when and where you can use it. A hygro meter is an essential tool in meteorological science. It has numerous commercial applications, but the main purpose of the device is to measure the amount of water vapor (moisture) in the air.

The main purpose of the instrument is to provide the amount of moisture in the air and to compare that number with the maximum amount of moisture that air, limited space or soil may possibly contain. If you have the question of how a hygro meter works, here is the answer. Like other moisture meters, hygrometers work with other quantities or measurements of temperature, mass and pressure, as they absorb moisture and serve as a dehumidifier.

Hygro meters are considered weather instruments with which the humidity can be measured. Over the centuries, these instruments have changed, evolved and adopted different varieties to meet users' needs. It was in the 14th century when one of the first models of hygro meters came onto the market. Leonardo da Vinci designed his early version of this device, which aimed to measure humidity.

He had a really clever design, revolving around a gauge that had absorbent and non-absorbent materials on each side. As the humidity increases, the side with the absorbent material gets heavier the more saturated it gets. The difference in weight was interpreted as a measure of the relative humidity.

Functionality of humidistats

Today, there are different types of hygro meters, and how they work depends on their design. For example, one of the types is a capacitive hygro meter. Devices classified in this form use other types of sensors. Capacitive Hygro Meters have been developed for applications where price, fragility, or footprint play a role. They therefore jeopardize the accuracy of reading moisture for the affordability of the device.

Capacitive hygro meters measure the influence of moisture on a metal oxide material. Often, they are also used to quantify the influence of moisture on the dielectric constant (or relative permittivity) of a polymer such as synthetic plastics. When calibrated, the sensors have an accuracy of plus or minus two percent relative humidity in the range of five to 95 percent relative humidity.

If not calibrated, the accuracy is up to three times worse. However, the sensors withstand high temperatures and the effects of condensation and are suitable for a variety of applications. However, these capacitance hygrometers have sensors that are easily contaminated and show signs of rapid aging.

Another sensor is resistive, which is less sensitive than capacitive sensors. These sensors measure the changes in the electrical resistance of a material caused by moisture in the environment. Resistance sensors require a more complex circuit board because they are not as sensitive as capacitive sensors. The accuracy depends on the resistance material used, but is usually up to plus / minus three percent relative humidity. The material also determines how robust the hygro meter is against condensation.

What is a hygro meter used for?

Hygrometers are considered useful tools that use the calculation and calibration of pressure and temperature changes. In combination, the percentage of moisture in the air is calculated as a percentage. A hygro meter is a useful device in office buildings and apartments as well as in manufacturing and industrial processes. These areas must ensure that the humidity does not change, as this can affect the production of materials. In addition, the devices can also serve as a dehumidifier.


As already mentioned, this type has two thermometers, one dry and one wet. The temperature difference is measured when the evaporation takes place in the wet flask, whereby its temperature falls below that of the dry flask. Psychrometers are useful devices for measuring humidity outdoors. They are also ideal for places that require dry conditions, eg. B. storage rooms.

Electric hygro meters:

These devices can be either resistive or capacitive. For resistive electric hygro meters, electricity flows through an in-air ceramic. At high humidity, the ceramic contracts by more water vapor, which leads to a change in resistance. Meanwhile, a capacitive electric hygro meter uses two plates between which there is air. The amount of moisture is measured by the ability of these metal plates to store electrical charges that directly affect moisture.

Dew point hygrometer:

These devices are used to measure the saturation of moisture in a gas. Usually they are used in places where the lowest humidity is to be found. Currently, they are considered the most accurate type of hygro meters. Hygro meters have become a popular device in industrial premises and greenhouses. However, these days they are also used in museums, humidors, saunas and incubators. Moisture can damage wooden musical instruments, which is why hygro meters are also used to care for pianos, violins, harps and guitars. Meanwhile, households can benefit from hygro meters as they help residents control humidity. Very low humidity can have a negative effect on skin and body. On the other hand, too high humidity promotes the increase of mildew and house dust mites. With these devices, homeowners can find out how to control the humidity in their environment with a dehumidifier.

Reading the device

Regardless of whether you use a hygro meter for weather observation or to measure indoor conditions, it makes sense to know how to read a hygro meter. For the best and most accurate results, these devices must be calibrated at least once a year. The relative humidity is calculated by comparing the numbers in a calculation table that corresponds to the ambient temperature with the difference between the temperatures given by the two thermometers.

Reading the hygrometer is not difficult but may vary depending on the type and model.

To read the result, look at the table on the front of the device. With digital hygrometers, you only have to set up the instrument about one meter above the ground. Leave the device for at least three minutes to allow it to adequately detect the air temperature. You do not have to do any further calculations as the device does this for you.

Your KlimaLex Team