The moisture-sensitive element is the simplest humidity sensor. There are two main types of moisture-sensitive elements: resistive and capacitive.
Humidity-sensitive resistors are characterized by a layer of film made of moisture-sensitive material on the substrate, when the water vapor in the air adsorbed on the moisture-sensitive film, the resistivity of the element and the resistance value are changed, using this feature to measure humidity.
Humidity-sensitive capacitors are generally made of polymer film capacitors, commonly used polymer materials such as polystyrene, polyimide, caseinate acetate fiber. When the ambient humidity changes, the dielectric constant of the moisture-sensitive capacitor changes, so that its capacitance also changes, and its capacitance change is proportional to the relative humidity.
Several types of humidity sensors in greater use:
Lithium chloride humidity sensor
Carbon moisture-sensitive element
Aluminum oxide hygrometer
Ceramic humidity sensor