| 摘要 |
An early warning signal is produced when there is a danger of ice forming on a road surface by means of a device comprising a temperature sensor for determining the ambient temperature, a sensor unit for determining the temperature and moisture of the road surface, a heatable sensor unit having a heating element and a moisture-detecting gap, and comparators for comparing the voltages supplied by the temperature sensors and the moisture sensors with reference voltages, comprises in addition thereto a sensor unit having a further moisture-detection gap, one or more elements for alternately cooling or heating this further moisture-detection gap, and a temperature sensor for determining the temperature of this further moisture-detection gap, as well as signal generators generating signals in response to the output signals of the comparators for indicating whether the road surface is dry, wet, or icy. The early warning signal is reliably given in advance of actual ice-formation solely as a function of the road surface temperature and of the condition of the moisture sensors. The response thresholds of those comparators which are associated with the moisture sensors are preferably varied as a function of the road surface temperature in order to allow for the influence exerted on the freezing point by thawing agents spread on the road surface. |
