IoT Sensors - Humidity

summarize

A very common IoT applicationtransducersIs humidity, as we all know, humidity is the concentration of moisture in the air, the size of the humidity affects our physical sensations, affecting the growth of plants, affecting the life cycle of the equipment; we are not dealing with humidity all the time, from smart phones to air quality monitoring systems; from the use of air conditioning to adjust the ambient humidity of the room so that we can be comfortable to the hospital for the patients who have difficulty breathing to maintain the right humidity; from high-tech chip production and From high-tech chip production and packaging and testing enterprises to maintain the humidity of the production environment to agricultural greenhouses in order to have a good environment for the survival of crops and set the humidity, and so on various industries, we can not do without humidity; a scientific study shows that: maintain indoor relative humidity > 40% will significantly reduce the infectiousness of the atomized virus.

Because humidity affects chemical, biological, and physical processes, the same amount of water vapor results in higher relative humidity in cold air than in warm air. The amount of water vapor contained in a package of air can vary greatly. For example, a nearly saturated piece of air may contain 28 g of water per cubic meter at 30 °C (86 °F), but only 8 g of water per cubic meter at 8 °C (46 °F). This amount is therefore measured by an air humidity sensor and converted into a readable data form for external use. There are three ways to define humidity:

Dew point Dp(Dew point)

The dew point, expressed in °C, is the temperature and pressure at which a gas begins to condense into a liquid. When air is cooled to the dew point by contact with a surface colder than air, water condenses on the surface. Devices called hygrometers are used to measure dew point over a wide range of temperatures. These devices consist of a polished metal mirror that cools as air passes through it.

Absolute humidity(AH)

Absolute humidity is the total mass of water vapor present in a given volume or mass of air. It does not take temperature into account. When air is saturated at 30 °C (86 °F), the absolute humidity in the atmosphere ranges from near zero to about 30 grams per cubic meter. Absolute humidity is the mass of water vapor divided by the volume of the air and water vapor mixture (refer to the following formula)

Relative humidity(RH)

Relative humidity is the ratio of the amount of water vapor in the air to the amount of water vapor the air may contain at a given temperature. It varies with air temperature: colder air can hold less vapor. Therefore, changing the temperature of the air will change the relative humidity even if the absolute humidity remains constant.

Cold air increases relative humidity and can cause water vapor to condense (the saturation point if relative humidity rises above 100%). Similarly, warmer air decreases relative humidity. Heating some air containing fog may cause the fog to evaporate as the air between water droplets becomes better able to hold water vapor.

Relative humidity is usually expressed as a percentage; a higher percentage means that the air-water mixture is more humid. Relative humidity is an important indicator used in weather forecasting of the likelihood of precipitation, dew, or fog. In hot summer weather, elevated relative humidity prevents the evaporation of sweat from the skin, thereby raising the apparent temperature of humans (and other animals). For example, based on the heat index, at an air temperature of 26.7 °C, the relative humidity of the 75% feels like 28.7 °C ± 0.7 °C.

Sensor Classification

Capacitive principle of operation

Resistive principle of operation

capacitive

Capacitive humidity sensors are one of the most common relative humidity sensors. Capacitive humidity sensors are designed to measure relative humidity by placing a thin metal oxide between two electrodes. When the relative humidity of the atmosphere changes, the electrical capacity of the metal oxide changes. These sensors are linear and they can measure relative humidity from zero to 100%. Capacitive humidity sensors can be used in weather, industrial or commercial applications.

resistive

Capacitive humidity sensors measure the electrical impedance of atoms by utilizing ions in salt. Changes in humidity result in changes in the resistance of the salt dielectric electrodes. These sensors are capable of storing an electrical charge and they are also one of the most common RH sensors.

The cost of these sensors is lower than other types, and they can be used in remote monitoring applications, such as large sites with large distances between signaling circuits and sensor elements.

thermal

Thermal sensors are categorized as types that measure AH (or absolute humidity). They are ideal for locations with high temperatures or corrosive environments. In order to measure the humidity of an environment using this type of humidity sensor, one thermal sensor measures the ambient air while the other is encapsulated in dry nitrogen gas. The difference between the two collected data then enables you to measure humidity. In other words, they measure absolute humidity by finding the difference between the thermal conductivity of dry air and humid air.

Sensor Manufacturers

Humidity sensor manufacturers are also many, domestic brand products are gradually some, but in the accuracy and quality above, there is still a big gap.

• United States (Honeywell) Honeywell
• Germany (SIEMENS) Siemens
• Sensirion, Switzerland
• Rotronic, Switzerland
• Germany (sera)
• United States (OMEGA)
• Japan (OMRON) OMRON
• Austria (E+E Elektronik) Igayi
• Japan (TDK)
• United States (Setra)
• China Huapu Microelectronics
• Osun Electronics
• Zhongke Galaxy Core

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