A basic resistive humidity sensor, also known as a resistive humidity element or humidity-sensitive resistor, is a type of sensor designed to measure relative humidity in the surrounding environment. It operates on the principle that certain materials' electrical resistance changes in response to changes in humidity. Here's how it works:
Sensor Material: The sensor is typically made of a hygroscopic material that absorbs or desorbs moisture from the surrounding air, depending on the humidity level.
Resistance Variation: The electrical resistance of this hygroscopic material changes as it absorbs or releases moisture. When humidity increases, the material absorbs moisture and swells, leading to an increase in its electrical conductivity and a decrease in its resistance. Conversely, when humidity decreases, the material releases moisture and contracts, causing its resistance to increase.
Wiring and Measurement: The sensor is integrated into an electrical circuit. It's connected in a resistor divider circuit, along with a known resistor. The voltage across the humidity-sensitive resistor is measured, and this voltage changes with the resistance of the sensor, which is in turn influenced by humidity.
Calibration: To convert the resistance change into a humidity reading, the sensor needs to be calibrated. This involves relating the resistance values at different humidity levels to corresponding known humidity values. Once this calibration curve is established, the sensor's resistance change can be used to determine the relative humidity in the environment.
Output: The output of the sensor can be an analog voltage or resistance value that changes with humidity. In some cases, it might also be digitally interfaced through analog-to-digital converters (ADCs) to provide digital humidity readings.
It's important to note that basic resistive humidity sensors might not be as accurate as more advanced sensor technologies like capacitive humidity sensors. They might also be influenced by temperature changes, which can affect their accuracy. However, they are relatively simple and cost-effective solutions for measuring humidity in a variety of applications, such as weather monitoring, environmental control systems, and industrial processes where high accuracy is not critical.