GB966769A - Improvements in the predicting of icy conditions on road and like surfaces - Google Patents

Abstract

966,769. Detecting icing conditions electrically. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 23, 1962 [May 23, 1961], No. 18523/61. Heading G1N. Ice formation on roads is predicted by measuring changes in electrical conductivity due to changes in thickness of a film of water on the road, or a similar adjacent surface, measuring the road surface temperature, and using these measurements to produce an output signal when a predetermined rise in conductivity occurs simultaneously with a road surface temperature near freezing point. The resistance between electrodes 11, 12, embedded in the road surface, indicates the wetness of the road surface and operates relay R2 to close contacts S2 at a predetermined wetness. Contacts S1 are closed when a temperature responsive device in or near the road surface indicates temperature near freezing point, thereby energizing relay R6 to energize a road heating circuit (not shown), Qr alarm circuit (not shown), through contact S6. If a road heater is provided a second heater 24 is simultaneously energized through contacts S<1>6. Conditions conducive to hoar frost formation may be detected by measuring the temperature difference between the road surface and the air, relay R6 operating whenever the road surface temperature is near freezing point and below the air temperature. Snow is detected using asphalt block 20 in which are embedded heater wire 24, pilot heater 23 and, at the surface, electrodes 21, 22 which are connected in parallel with electrodes 11, 12. Pilot heater 23 is energized to melt snow in the centre of the block and the resistance between electrodes 21, 22 controls relay R2. Alternatively, block 20 may be omitted and the pilot heater arranged under electrodes 11, 12. A further alternative is to omit contacts S3 and use block 20 for frost detection. In this case pilot heater 23 is energized periodically (e.g. 15 minutes per hour) and the block is thermally insulated from the road so that between heating periods it cools more rapidly than the road and dew or frost is deposited on it first, the frost being subsequently melted. Relay R6 may also be operated via contacts S4 when the temperature beneath the road surface approaches freezing point. Contacts S5 are for manual control. The device may be automatically disabled if de-icing chemicals lower the resistance between electrodes 11, 12 below a certain value. The apparatus is preferably fail-safe.