The humidity sensor has another name - hygrometer. It is a device for measuring humidity levels. The latter indicator is important both for everyday life and for production processes.
In the home, the humidity determines the well-being of the inhabitants of the house. With regard to production processes, some devices are important to the level of humidity, for which they are even carried out their adjustment.
Contents
Terminology
It is necessary to understand what air humidity sensors are, because not all users understand what they are used for.
There are absolute and relative humidity. The first one means the exact amount of water in the air (measured in g/cc). At the same time, the moisture content can also be determined as a percentage. This indicator has a limit - 100%. This is the highest value, which is also called the maximum saturation threshold. Another name for it is the moisture capacity. The condensation process starts just from this limit.
There is a relationship between the moisture capacity and the temperature of the medium. The higher the temperature, the more moisture can collect in the same volume of air. This is why both digital and analog instruments are often equipped with an additional temperature sensor.
The ratio of the moisture content to the absolute humidity is the relative humidity of the air. When these values are equal to each other, a condition called "dew point" occurs.
This terminology should be understood before you go out to buy a device, since sensors are selected based on a number of criteria.
Types of Sensors and How They Work
Moisture sensors come in different types. There are 4 main types of such devices on sale:
- Capacitive moisture sensor. Represents an air condenser. Devices are used both for industrial equipment and for household appliances. Structurally, such a hygrometer consists of a substrate, on which there is a thin-film polymer element. The substrate is made of ceramic, glass or silicon. The advantages of these devices are that they can operate at high temperatures and their resistance to chemical vapors is important in industry.
- Resistive sensor. Its principle of operation is based on a change in the resistance index of a hygroscopic material, which occurs depending on the level of moisture content. Detectors of this type are most commonly used in the home.
- Psychometric sensor. In this case, its operation is based on the fact that heat is lost during evaporation. This design uses 2 detectors: dry and wet. The temperature difference is measured, which allows you to determine the level of moisture in the air. Once upon a time, such meters were used less frequently because you had to constantly check with tables. Today, they are digital instruments of high accuracy, and they are not at all difficult to use.
- Aspiration sensors. They are similar to psychometric ones, but their design includes a fan that is responsible for the forced injection of gas or an air mixture. It is advisable to install such devices where the air movement is weak and intermittent.
Regardless of whether a capacitive relative humidity sensor or a psychometric device, the user is interested in their reliability. That is, how well this device works in damp conditions, what factors can affect the accuracy of measurements, etc.
Design of Resistive Type Detectors
Moisture detectors of this type must record changes in electrical resistance in a hygroscopic environment. These are materials such as salt, conductive polymer, other types of substrate. Most often the second option is still used. To understand the principles of determining - how to measure humidity measurements with this device, it is necessary to consider its structure.
Moisture sensors of the resistive type are electrodes made of a metal alloy, which are applied to a substrate using a photoresistor, or the second option - the electrodes are wound on a plastic or glass cylinder. The substrate is coated with the previously mentioned conductive polymer or saline solution. Sometimes the substrate is treated with another chemical compound, including acid.
When water vapor hits the sensing elements, the ionic groups decay, which increases the electrical conductivity. Its measurement helps to establish the level of humidity.
A sensor of this type works fast enough. For most models of such equipment, the response time is 10-30 seconds. The resistance range can vary from 1 kOhm to 100 mOhm. Portable multicomponent sensors have fewer functions than their more expensive counterparts. But for household purposes this is enough.
The use of an electronic digital air humidity sensor of this type makes it possible to achieve good measurement accuracy. The equipment is calibrated in a special computer system.
Resistive sensors are resistant to the environment. They can operate from -40°C to +100°C. In addition, such devices normally last for at least 5 years, even in production, not to mention domestic use.
But the point at which they are installed does matter. If they are constantly exposed to chemical vapors or oils, the service life is lower.
A brief overview of the devices available on the market and their applications
Looking at how condensation gets on the mirror in the bathroom, people think about installing a humidity meter in the room. Especially when there are several electrical appliances running there at once. To choose a humidity sensor in the bathroom should be approached responsibly.
Among the devices of the resistive type is considered a good option model SYH-2RS. It can operate at temperatures up to +85 ° C and has good technical characteristics. The error of the sensor is only about 5%. One of its advantages is its compactness.
The thickness of the housing does not exceed 2.9 mm, length - about 10 mm, after installing the device is almost invisible, that is not spoil the interior. It operates from a household network of 220 V.
Like many modern sensors, it can even overcome the main disadvantage of resistive devices, which is that the accuracy of their readings decreases in the presence of condensation. However, more often cheaper Chinese analogs are used instead of this model.
Among the products made in the Celestial Empire, most of the sensors are produced by unknown manufacturers. Of the Chinese ones, the most popular are DHT22 and DHT11. The second option is cheaper, but the first is of higher quality.
Such devices are put simultaneously with the fan. Therefore, some apartment owners just save money on sensors, preferring Chinese products, although they have a smaller temperature range and service life can not reach up to 5 years.
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