1. BME680 HUMIDITY SENSOR
EDDIE SHEA
RUCHEN TANG
SEAN SWALVE

2. Some useful definitions
Absolute humidity is the mass of water vapor divided by the mass of dry air in a certain volume of air at a specific temperature
Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature
(Amount of water vapor / the amount needed for saturation)

3. Thermal Conductivity Humidity Sensors
Use the difference in specific heat between dry air and moist air to calculate the absolute humidity

5. Thermal Conductivity Humidity Sensor
Respond to any gas that has thermal properties different from those of dry nitrogen gas, which will affect the measurements.
Suitable for relatively high temperature and provides greater resolution at T> 90 ℃ than do capacitive & resistive sensors
±3g/m^3 accuracy on absolute humidity
(about ±5%RH at 40 ℃ and 0.5%RH at 100 ℃)

6. Capacitive Humidity Sensor
Dielectric material sandwiched between two electrodes
Dielectric material is able to absorb water vapor
The dielectric material absorbs water vapor until it is in equilibrium with the ambient water vapor concentration
Absorbing more water vapor raises the capacitance value by a known value

7. Capacitance vs Relative Humidity

8. BME680 Humidity Sensor Specs

9. References