Learn in the textbookDetection Devices (Distance and Environmental-Quantity Sensors)
DefinitionA humidity sensor (湿度センサー) measures a value tied to how much water vapor the air holds (humidity) and turns it into an electrical signal.
ExplanationMost output relative humidity (%), the share of water vapor compared with the most the air can hold at that temperature. Since relative humidity shifts with temperature, it is often combined with a temperature sensor in a single temperature-humidity sensor. It is used for automatic humidifier and dehumidifier operation and to help prevent condensation and mold in greenhouses and warehouses.
AnalogyWe sense how damp the air is from how fast the laundry dries; this device does the same job with numbers.
Memory hookThe "60% humidity" in a weather forecast is relative humidity: it shows not the amount of water itself but how full the container called air is.