Operating range of the RH element

The RH sensor is specified to work over the entire humidity range of 0 to 100% RH for the temperature range –40 to 70 °C. The sensor will perform best in humidity in the range of 20 to 80% RH.

In common with most types of unheated, polymetric humidity sensors, the sensor can exhibit a temporary change in calibration, sometimes called long-term hysteresis. Long-term hysteresis is when the sensor is subjected to prolonged periods of high humidity and condensation. The sensor calibration may be temporarily altered, normally resulting in a change of less than +3% RH. The combination of high humidity and high temperature accelerates this change. However, upon returning to more normal ambient conditions, the calibration will settle back to the normal calibration over the course of several hours or exceptionally a few days.

In laboratory conditions, it is possible to speed up the return to the normal calibration by reconditioning the element alone using this process:

1. Bake the sensor at 100 to 105 °C at < 5% RH for 10 hours.

2. Then re-hydrate at 20 to 30 °C at ~ 75% RH for 12 hours.

The exact timing of these steps is not critical.