| 摘要 |
PURPOSE:To detect the freezing of a road surface with a high probability even in a sudden change in weather in the night after a rainfall or a snowfall by judging the freezing when both a road surface temperature and the difference between the road surface temperature and an atmospheric dew point temperature are below 0 deg.C and a high humidity duration has a predetermined condition. CONSTITUTION:A road surface temperature signal output unit 1, an atmospheric temperature signal output unit 2 and an atmospheric humidity output unit 3 respectively convert a road surface temperature, an atmospheric temperature and an atmospheric humidity to signals. An arithmetic unit 5 calculates the difference between the road surface temperature and an atmospheric dew point temperature calculated by a dew point temperature calculator 4. A freezing judging unit 6 judges a freezing based on the data of the arithmetic unit 5 and the output unit 1 when the road surface temperature and the difference between it and the atmospheric dew point temperature are both below 0 deg.C. On the other hand, when the duration of a high humidity condition exceeds a prescribed time, a humidity condition judging unit 9 outputs a freezability signal based on atmospheric humidity data from the output unit 3 stored in an atmospheric humidity storage 8. A freezing judging unit 10 judges the freezing when a time at which the road surface temperature from the output unit 1 becomes below 0 deg.C is within a prescribed time from a high humidity duration ending time. A freezing alarm is outputted in response to the outputs of the judging units 6 and 10.
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