| 摘要 |
A method and an apparatus for determining the covering on a road surface. A measurement signal is fed into a pair of electrodes inlaid in the road surface and acting as a detector (5), whereby the ratio of the measurement current to the voltage formed across the detector (5) is determined in order to establish the conductivity of the covering on the road surface. The signal fed into the detector (5) is a low-voltage and low-frequency symmetric alternating voltage signal, and the electric polarization between the poles, caused by the measurement current, is measured in order to determine the thickness of the covering on the road surface. The apparatus comprises a switch (3) for opening the conductivity measurement circuit (6) for the purpose of measurement of the surface signal, a detector polarity reversing circuit (4) for reversing the direction of the measurement current, a surface signal measurement circuit (7) for the measurement of the thickness of the covering on the road surface, as well as an alarm logic circuit (8) arranged to indicate possible freezing of the road on the basis of the voltage values of the conductivity and surface signals. |
