A basic resistive humidity sensor, also known as a humidity-sensitive resistor or a hygrometer, is a device designed to measure the relative humidity (RH) of the surrounding air. The function of this type of sensor is based on the principle that certain materials' electrical resistance changes with variations in humidity levels.
Here's how it works:
Sensing Material: The sensor contains a hygroscopic (moisture-absorbing) material with properties that make its electrical resistance sensitive to humidity changes. Common materials used in these sensors include ceramics, polymers, and organic compounds like polyimide or cellulose.
Electrical Conductivity: When the humidity in the environment changes, the sensing material absorbs or desorbs moisture, causing its physical structure to expand or contract. This, in turn, affects the material's electrical conductivity.
Resistance Variation: As the moisture content changes, the electrical resistance of the sensing material changes proportionally. Higher humidity causes the resistance to decrease, and lower humidity leads to an increase in resistance.
Calibration: To convert the resistance change into a usable humidity reading, the sensor is calibrated during the manufacturing process. Calibration involves measuring the sensor's resistance at known humidity levels and establishing a relationship between resistance and humidity.
Output: The output of the resistive humidity sensor is typically an analog signal representing the humidity level. This signal can be read by a microcontroller or other electronic components, and the humidity value can be displayed or used for further processing.
Applications: Basic resistive humidity sensors find applications in various fields, including home automation, HVAC (Heating, Ventilation, and Air Conditioning) systems, weather monitoring, industrial process control, and agricultural applications.
It's worth noting that while resistive humidity sensors are simple and cost-effective, they may have some limitations, such as sensitivity to temperature changes and calibration drift over time. More advanced humidity sensors, like capacitive or digital humidity sensors, are often used in applications requiring higher accuracy and reliability.