A humidity sensor (or hygrometer) measures and reports both humidity and air temperature. The ratio of humidity in the air to the highest amount of humidity at a certain temperature is called relative humidity. Relative humidity becomes an important factor in certain conditions.
Humidity sensors work by detecting changes that alter electrical currents or air temperature.
There are three types of basic humidity sensors:
Three types of sensors monitor instantaneous changes in the atmosphere to calculate air humidity. We discuss its different types in detail:
A capacitive humidity sensor measures relative humidity by placing a thin strip of metal oxide between two electrodes. The electrical capacity of metal oxides varies with the relative humidity of the atmosphere. Climate, trade and industry are among the most important applications.
Capacitor type sensors are linear and can measure relative humidity from 0% to 100%. The measurement here is a complex circuit and regular calibration. However, it is less of a hassle for designers than accurate measurements, and therefore they dominate atmospheric and process measurements. These are the only types of full humidity measuring devices with full range up to 0.% relative humidity. This effect of low temperatures often leads to their use in a wide temperature range without compensating for the active temperature.
Resistant moisture sensors use ions in salts to measure the electrical impedance of atoms. Measure the resistance of the electrodes on each side of the salt medium by changing the humidity.
Two thermal sensors conduct conductivity based on the humidity of the surrounding air. One of the sensors is located in dry nitrogen and the other measures the ambient air. Measures the difference between the two humidities.
Tips on the performance of the humidity sensor
Colometric: The electrolyte is formed by the absorption of water and as a result the current level is proportional to the humidity in the air.
Gravity: The desiccant is exposed to humid air, resulting in weight gain by the desiccant. Weight gain is related to the amount of moisture.
Microwave / Infrared: A signal is transmitted as humidity increases. Damping (attenuation) is a sign of moisture in the environment.
Some necessary parameters to select
First you need to know what a humidity sensor is and how it works, the next step will probably be to check its performance. And how do you do it? By working through some of the parameters listed below.
Each sensor has 9 points based on the system with its own calibration curve. Basically the pros versus the cons of a particular sensor.
This shows the voltage deviation from the BFSL value and the measured output voltage value converted to relative humidity.
Measurements often cause the sensor to be out of sync. However, for a sensor to be useful, it must provide reliable measurements.
The measurements of a sensor should be such that they do not differ from each other. The repeatability of a measurement with the same results between measurements is a single value.
Typically, time is increased by a sensor to 66% (rise time) or decrease to 33% (fall time) of the maximum output voltage, known as the response time.
The applications of humidity sensors are many and wide
The applications of humidity sensors are very wide. People with diseases that are affected by humidity, monitoring and preventive measurements in the home, use a humidity sensor. A humidity sensor is also found as part of home heating, ventilation and air conditioning (HVAC) systems. They are also used in offices, cars, humidifiers, museums, industrial spaces and greenhouses, as well as in meteorological stations to report and forecast the weather.
We mention some of the following projects for reference:
Here is a simple humidity indicator and controller. In industries such as textiles, changes in moisture content have a direct effect on fabric properties such as tensile strength, elasticity, fiber diameter and friction. Cotton and sheets have a high relative humidity (RH) of about 70-80% because they are very fragile. Wool requires an RH level of about 65%. While silk requires between 65 and 70%. With this circuit, you can not only control the humidity between 30 to 90% RH, but also control it.
Refrigerator temperature and humidity index
When the small sniffer device collects temperature and humidity from inside the refrigerator and transfers it from the RF junction to the receiving unit nearby. The receiving unit checks the received code, determines the appropriate sniffer device and shows the available temperature and humidity. We can measure the temperature and humidity inside the refrigerator using a natural temperature-humidity indicator, but the relative humidity in this case can be inaccurate.
Indicators and humidity
Here is a simple humidity indicator and controller. In industries such as textiles, changes in moisture content have a direct effect on fabric properties such as tensile strength, elasticity, fiber diameter and friction. Therefore, the process is performed only at a permissible humidity. Depending on the type of fabric and the process performed, the specific moisture content varies. Cotton and fabric should be processed at very high relative humidity (RH) of about 70-80% because they are very brittle. Wool requires an RH level of about 65%. Silk is processed between 65 and 70%. With this circuit, you can not only control the humidity between 30 to 90% RH, but also control it.
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