There are various kinds of humidity sensors. Alps Alpine's humidity sensors detect the amount of water vapor in the air and convert it into an electrical signal. Here we introduce the sensing principles and features of Alps Alpine's humidity sensors.

What is Humidity?

Humidity is the amount, or percentage, of water vapor present in the air and usually refers to relative humidity. Another measure is absolute humidity.

Relative humidity (%RH): Amount of water vapor in the air at a given temperature ÷
      Amount of water vapor needed for saturation at that temperature

Absolute humidity (kg/kg): Mass of water vapor ÷ Mass of dry air

Alps Alpine's humidity sensors measure relative humidity.

The difference between relative humidity and absolute humidity can be illustrated using the following example. As air contracts or expands with a change in temperature, relative humidity changes but absolute humidity does not because the water vapor content is the same.

Humidity Sensing Methods

Humidity sensors measure humidity in a variety of ways. Alps Alpine's humidity sensors are electrical and use change in capacitance.

Principles of Alps Alpine Humidity Sensors

Capacitive humidity sensors like Alps Alpine's consist of two electrodes separated by a dielectric material (forming a capacitor). Humidity is measured by applying AC voltage between the electrodes and ascertaining the change in capacitance between the electrodes resulting from a change in permittivity (dielectric constant) of the dielectric material due to absorption of moisture. By contrast, resistive humidity sensors use the change in conductivity of the dielectric material resulting from absorption of moisture.

A built-in IC converts capacitance values (C) obtained via the sensor into voltage (V).

Features of Alps Alpine Humidity Sensors

Industry-Smallest (Alps Alpine research, December 2019)

Developing and manufacturing in-house, Alps Alpine has realized the industry's smallest humidity sensors using its own semiconductor processes to form thin-film capacitors like the above on silicon wafers.

Example: HSHCAL001B

High Linearity

Compared to other types of humidity sensor, Alps Alpine's humidity sensors deliver high linearity of output.

Applications and Varieties of Alps Alpine Humidity Sensors

A humidity sensor's function is naturally to measure a level of humidity, but humidity sensors are also used to detect ingress of moisture. Applications of the former include air-conditioning systems and refrigerators, while uses of the latter are detection of moisture ingress in printer paper feed mechanisms and waterproof equipment.

Alps Alpine's Humidity Sensor Varieties

Type	Part number	Output	Temperature measurement	Moisture-proof coating	Other features
SMD	HSHCAA006A	Analog	-	-	-
	HSHCAL001B	Digital(I2C)	○	-	-
Connector connection (Module with sensor already mounted)	HSHCAA114A	Analog	○	○	Secure connector locking
	HSHCAL101B HSHCAD140A	Digital(I2C)	○	○	-