Preh Defogging Sensor (http://rbi.ims.ca/4927-545). Detecting window fogging in vehicles before the occurrence of visible condensation requires humidity and temperature sensors, as well as computer calculations. Mounted on the interior of the vehicle’s windshield, the humidity-sensitive element measures the relative humidity directly on the windshield. Using infrared technology, the sensor detects windshield fogging before it becomes visible to the human eye. A Negative Temperature Coefficient (NTC) thermistor reads the windshield temperature. With the data from the sensor the vehicle’s heating, ventilating and air conditioning system provides an optimal vehicle environment that takes into account humidity, as well as temperature.