how do humidity sensors work?
2024-11-19 14:56:28 993
Contents:
1. What is the humidity sensor
2. Working principle of the humidity sensor
2.1 Capacitive humidity sensor
2.2 Resistive humidity sensor
2.3 Thermal conductivity humidity sensor
2.4 Optical humidity sensor
3. How does the humidity sensor work
4. Advantages and disadvantages of the humidity sensor
5. This section describes the application of the humidity sensor
6. Conclusion
Humidity sensor is a very important part of modern environmental monitoring and control system, it has a wide range of applications in weather forecast, agricultural production, industrial manufacturing, medical health, smart home and other fields. You may have heard of humidity sensors, but do you have any idea how they work and what type of sensors they are? Today, Chipqry is here to introduce you, hoping to help you better understand this small but powerful component.
1. What is the humidity sensor
The humidity sensor is an electronic device that can detect the relative humidity (RH) or absolute humidity (AH) in the environment, and converts the humidity change into an electrical signal through the built-in induction element, and outputs it to the control system or display device. Such sensors play an important role in many fields, such as weather forecasting and climate research in meteorological monitoring; Used in agricultural production to monitor soil moisture and crop growth environment; Used in industrial production to control the humidity of the production environment to ensure product quality; Used in healthcare to monitor the humidity of the patient's living environment to ensure patient comfort; It is used to automatically adjust indoor humidity and improve living comfort in smart homes.
2. Working principle of the humidity sensor
The working principle of the humidity sensor varies according to its type, but the basic principle is to reflect the change of humidity through a change in some physical or chemical properties.
2.1 Capacitive humidity sensor
Capacitive humidity sensors use capacitance changes caused by humidity changes to measure humidity. Inside the sensor is a capacitor in which one of the electrodes is porous and absorbs water. When the ambient humidity changes, the dielectric constant of the dielectric changes, resulting in a change in the capacitance value of the capacitor.
The relationship between capacitance C and relative humidity RH can be expressed by the following formula: C = C0+ k⋅RH
Where C is the initial capacitance value, k is the scale factor, and RH is the relative humidity.
2.2 Resistive humidity sensor
Resistive humidity sensors use changes in resistance caused by changes in humidity to measure humidity. There is a resistance material inside the sensor, and when the ambient humidity changes, the resistance value of the resistance material changes.
The relationship between resistance and relative humidity can be expressed by the following formula: R=R0⋅e−k⋅RH
Where the initial resistance value, k is the proportional coefficient, and RH is the relative humidity.
2.3 Thermal conductivity humidity sensor
The thermal conductivity sensor uses the change in thermal conductivity caused by the change in humidity to measure humidity. Inside the sensor are two heating elements, one for reference and the other for measurement. When the ambient humidity changes, the thermal conductivity changes, resulting in a change in the temperature distribution.
The relationship between and relative humidity RH can be expressed by the following formula: ΔT=Tref−Tmeas=k⋅RH
Where, the reference temperature, , k is the proportional coefficient, and RH is the relative humidity.
2.4 Optical humidity sensor
Optical humidity sensors use changes in light refractive index caused by changes in humidity to measure humidity. There is an optical element inside the sensor, and when the ambient humidity changes, the refractive index of the light changes, resulting in a change in the propagation path of the light.
The relationship between the refractive index n and the relative humidity RH can be expressed by the following formula:
Where the initial refractive index, k is the proportional coefficient, and RH is the relative humidity.
Measurement method
Humidity sensor measurement methods mainly include:
Relative humidity (RH) : Measures the amount of water vapor in the air as a percentage of the saturated water vapor content.
Absolute humidity (AH) : Measures the amount of actual water vapor in the air, usually expressed in grams per cubic meter.
Dew point temperature: The temperature at which water vapor in the air reaches saturation.
Output signal
The output signal of the humidity sensor can be an analog signal or a digital signal, where the analog signal is usually a voltage or current signal of 0-5V or 4-20mA. The digital signal is usually the output signal of digital communication protocols such as I2C, SPI or UART.
3. How does the humidity sensor work
Capacitive humidity sensor
Capacitive humidity sensors have a capacitor composed of two metal plates filled between the two metal plates with a hygroscopic polymer or other material as a medium. When the humidity in the air increases, the medium absorbs more water molecules, resulting in an increase in the dielectric constant and an increase in the capacitance value. On the contrary, if the humidity is reduced and the medium releases water molecules, the dielectric constant decreases, the capacitance value also decreases. By measuring the capacitance value change of the capacitor, and through the corresponding circuit conversion, the final output of the electrical signal corresponding to the humidity.
Resistive humidity sensor
Resistive humidity sensors usually use a hygroscopic material as the sensing element. The resistance of this material changes with the humidity in the surrounding environment. As humidity increases, the material absorbs water, causing its resistance to decrease. When the humidity decreases, the material loses water and its resistance rises again. By monitoring this change in resistance, the magnitude of relative humidity can be calculated.
Thermal conductivity humidity sensor
Thermal conductivity humidity sensors take advantage of the high thermal conductivity of water vapor. The higher the humidity, the greater the concentration of water vapor in the air, and the greater the thermal conductivity. Emit a constant amount of heat. Measure the speed of heat transfer under different humidity conditions. The humidity value is determined according to the change of heat conduction rate.
Fiber optic humidity sensor
Fiber optic humidity sensors usually contain a light source, an optical fiber, and a light detector. One end of the fiber is coated with a hygroscopic material whose refractive index changes with humidity. The light emitted by the source is transmitted through the fiber to an area coated with a hygroscopic material. When the ambient humidity changes, the refractive index of the hygroscopic material changes, which affects the propagation path and intensity of light in the fiber. The light detector receives the light signal transmitted through the hygroscopic material and converts the light signal into an electrical signal. By analyzing the electrical signal, the current humidity value can be calculated.
Grating humidity sensor
The grating humidity sensor utilizes the characteristics of fiber Bragg grating (FBG). FBG is a special fiber grating whose reflected wavelength changes with the physical properties of the fiber (such as length, refractive index, etc.). The broadband light emitted by the light source is transmitted to the FBG through the fiber. FBG reflects a specific wavelength of light, which depends on the physical properties of FBG. When the ambient humidity changes, the hygroscopic material on the FBG absorbs or releases water, causing the physical properties of the FBG (such as the refractive index) to change. This change causes the wavelength reflected by the FBG to shift. The light detector receives the reflected light and measures the change in the reflected wavelength. By analyzing the change in reflected wavelength, the current humidity value can be calculated.
4. Advantages and disadvantages of the humidity sensor
Capacitive humidity sensor
Advantages: fast response, high precision and good stability.
Disadvantages: It is greatly affected by temperature, and temperature compensation is required.
Resistive humidity sensor
Advantages: Simple structure, low cost, easy to integrate.
Disadvantages: Slow response and low accuracy.
Thermal conductivity humidity sensor
Advantages: not affected by temperature, good stability.
Disadvantages: Slow response and high power consumption.
Optical humidity sensor
Advantages: high precision, fast response, free from electromagnetic interference.
Disadvantages: complex structure and high cost.
5. This section describes the application of the humidity sensor
In meteorological monitoring, high-precision capacitive humidity sensors are usually used to monitor humidity changes in the atmosphere and provide weather forecasting and climate research data. The capacitive humidity sensor has high response speed and high precision, which is suitable for the high requirements of meteorological monitoring.
Low-cost resistive humidity sensors are commonly used in the agricultural production industry to monitor soil moisture and crop growth environment, and guide irrigation and fertilization. The resistive humidity sensor is simple in structure and low in cost, suitable for large-scale agricultural applications.
In industrial production, the use of stable thermal conductivity humidity sensors to control the humidity of the production environment to ensure product quality. Thermal conductivity humidity sensor has good stability and is not affected by temperature, which is suitable for industrial production environment.
Healthcare uses high-precision optical humidity sensors to monitor the humidity of the patient's living environment and ensure patient comfort. The optical humidity sensor has high precision and fast response speed, which is suitable for the high precision requirements of medical care.
Smart homes use fast-responding capacitive humidity sensors to automatically adjust indoor humidity and improve living comfort. The capacitive humidity sensor has a fast response speed and is suitable for the rapid adjustment needs of smart homes.
6. Conclusion
Humidity sensor is an indispensable equipment in modern environmental monitoring and control system, its working principle and types are diverse, suitable for different application scenarios. It is hoped that through the introduction of this content, readers can better understand and master the humidity sensor, so as to provide strong support for the research and application in related fields.
