This sensor measures the resistance of a platinum resistance wire and uses a calibration (for resistance vs temperature) to determine the temperature. Compared to the "slow" sensors (HARCO), the sensor head is not heated and the wire is in better thermal contact with the air, so the sensor responds to temperature change much faster. However, because it is not anti-iced, it develops problems sooner in icing conditions and it is still more sensitive to measurement errors in clouds. (See the tutorial referenced in the "Documentation" section at the bottom of this page.) Also, the sensing wire is more often damaged during flight in graupel, so the sensor is normally not used if graupel particles are likely to be encountered.
The following is a photograph of the sensing element that is attached to the fuselage of the aircraft:
Annual resistance calibrations in RAF reference bath, transfer to ADS3 via resistance box.
