A basic resistive humidity sensor, also known as a resistive humidity sensor or a humidity-sensitive resistor, is a type of sensor used to measure the relative humidity (RH) of the surrounding environment. It operates on the principle that the electrical resistance of certain materials changes in response to changes in humidity levels.
The basic function of a resistive humidity sensor involves the following steps:
Sensing Material: The sensor contains a humidity-sensitive material, often a hygroscopic substance like polymers or ceramics. These materials absorb or release moisture from the air based on the humidity level.
Resistance Variation: The electrical resistance of the sensing material changes as it absorbs or releases moisture. When humidity increases, the material absorbs moisture and its resistance decreases. Conversely, when humidity decreases, the material releases moisture and its resistance increases.
Measurement Circuit: The sensor is connected to a measurement circuit, which usually includes a known voltage source and a measurement device to monitor the resistance changes. The resistance of the sensing material is often used to create a voltage divider circuit with a known reference resistor. The resulting voltage across the sensor is then measured.
Calibration: Before using the sensor, it's important to calibrate it to accurately convert the resistance changes into relative humidity values. This involves correlating the resistance values at various humidity levels to their corresponding relative humidity percentages.
Output: The output of the resistive humidity sensor is typically an analog voltage that corresponds to the current humidity level. This output can then be converted to a digital signal using an analog-to-digital converter (ADC) if necessary.
It's worth noting that while basic resistive humidity sensors are simple and cost-effective, they might have limitations such as sensitivity to temperature changes, calibration drift over time, and relatively slower response times compared to more advanced humidity sensing technologies like capacitive or digital sensors. Despite these limitations, resistive humidity sensors are still widely used in applications where high accuracy and precision are not critical, such as certain industrial processes, consumer products, and environmental monitoring.