The envelope should not touch the sensor surface. The leads are difficult to seal. These semi-permeable membranes will lengthen the response time of the thin film sensors from about a minute to about twenty minutes. Calibrating RH sensors RH sensors are notoriously unreliable. They MUST be calibrated on installation and about every six months thereafter.
Calibration involves checking the accuracy at at least two RH values.
The usual method is to use saturated salt solutions .