A basic resistive humidity sensor, also known as a humidity-sensitive resistor or a hygrometer, is a type of electronic sensor designed to measure the relative humidity (RH) of the surrounding air. It operates on the principle that certain materials' electrical resistance changes with variations in humidity.
The main function of a basic resistive humidity sensor is to provide an electrical output that corresponds to the relative humidity level. Here's how it works:
Sensing Material: The sensor contains a humidity-sensitive material, typically a hygroscopic substance, which absorbs or desorbs moisture based on the humidity level in the environment. Common sensing materials include polymers like polyimide or metal oxides like aluminum oxide.
Resistance Variation: As the humidity changes, the sensing material either expands or contracts, causing its electrical resistance to vary. In most cases, an increase in humidity leads to a decrease in resistance, and vice versa.
Electrical Circuit: The sensor is integrated into an electrical circuit. The sensor's resistance forms part of a voltage divider circuit or a Wheatstone bridge circuit.
Output Signal: The electrical resistance variation results in a corresponding change in the output voltage of the circuit. This output voltage is calibrated to provide a linear relationship between the sensor's resistance and the relative humidity level.
Measurement and Calibration: To convert the electrical output into a meaningful humidity reading, the sensor requires calibration. Calibration involves subjecting the sensor to specific humidity levels and recording the corresponding electrical output. A calibration curve is then established to map resistance values to relative humidity percentages.
Applications of basic resistive humidity sensors include weather monitoring, climate control systems, indoor air quality monitoring, industrial process control, agriculture, and other applications where knowing the relative humidity level is essential for maintaining certain conditions or optimizing processes. It's important to note that while basic resistive humidity sensors are cost-effective and simple to use, they may have limitations in terms of accuracy and long-term stability compared to more sophisticated humidity sensing technologies.