Can the RH sensor measure humidity below 0C? And how can it be tested?
Yes, the sensor works below 0C. The accuracy drift/temperature must be considered. Testing the RH Sensor below 0C is difficult as most RH chambers cannot control the RH level accurately if not at all when temperature is lowered to 0C or below. To check for accuracy when measuring below 0C, a chilled mirror hygrometer is recommended.