Importance

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Abstract

Sensor and reference wires are directly exposed to the airflow past a vehicle. The wires are electrically conductive, and each has a resistance varying with its temperature. A continuous fixed voltage is passed through the reference wire. A short pulse of greater constant voltage is passed through the sensor wire, the voltage of sufficient magnitude to cause the rapid heating of the sensor wire during the pulse. The resultant rate of heat of the sensor wire, and its final temperature at the end of the pulse, is determined by whether ice or water is on the sensor wire. Circuitry is provided to generate an ice present signal when the difference in current flow during the pulse through the sensor wire and through the reference wire is of such magnitude and sign as to indicate that ice was in contact with the sensor wire. Due to water's heat of fusion, the effect of ice on the sensor wire is readily distinguished from the effect of water. In one embodiment a probe assembly is provided which includes a probe tube extending at an angle to the direction of movement of the vehicle. The sensor and reference wires are positioned in separate thread grooves for protection and wound repeatedly around a portion of the probe tube. A heater is fitted in a hollow cavity of the probe tube to facilitate melting of ice which forms on the sensor wire.

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First Claim