Introduction
The capacitive relative humidity sensor is a very common humidity measurement technology. This technology is found in around 75% of all humidity sensors.
How It Works
This type of humidity sensor is built from a piece of dielectric material sandwiched between two electrodes in the form of conductive plates to form a capacitive device. The dielectric material is usually made from a plastic or other type of polymer.
The dielectric material absorbs or releases water moisture in proportion to the atmospheric relative humidity. This changes the capacitance. An increase of moisture raises the capacitance and conversely a reduction in moisture reduces the sensor's capacitance.
The capacitive sensor element is wrapped top and bottom with protective layers during the manufacture of this type of sensor. When produced as a MEMS[3] package, this is attached to onboard capacitance measuring circuitry and an external interface such as serial I2C or SPI.
Advantages
It has many advantages including:
- Low cost, low power consumption.
- High accuracy and stability.
- Rapid response to humidity changes.
- Can withstand temperatures below 0°C, requiring minimal maintenance over time.
- Independent of barometric pressure.
Disadvantages
Even good things usually have some disadvantages:
- Temperature fluctuations affect sensitivity and accuracy.
- Sensitive to corrosive gases and other chemicals in the atmosphere.
- Can become contaminated with dust and other contaminants.
- Long term stability can become an issue as they age.
- High humidity or condensing conditions leads to lower response times.