At what rate do humidity sensors commonly drift?

• A. 5% per year.
• B. 0.1% per year.
• C. 1% per year.
• D. 10% per year.

Answer: (C)

Long-term stability of humidity sensors is about how their readings slowly shift with age and exposure. For the commonly used humidity sensors, the typical drift is about 1% relative humidity per year. In practice, calibrate a sensor at a given humidity today, and after a year it might read roughly one percent higher or lower under the same conditions. This moderate drift comes from aging of the sensing materials, changes in the dielectric or polymer layers, hysteresis effects, and temperature influences. Rates around 0.1% per year do occur in some high-end or tightly controlled devices, but 5% or 10% per year would indicate poor stability and would require more frequent recalibration or a different technology.