| 摘要 |
<p>Detection of wet and icy surface conditions on the surface of a pathway using a block (3) of electrically insulative material embedded in the pathway with its top surface (15) exposed to atmospheric precipitation A sensor electrode (9) is encapsulated in the block (3) and is positioned a predetermined distance beneath the top surface (5) of the block (3) so that an accumulation of atmospheric precipitation on the top surface (5) affects the capacitance and conductance between the sensor electrode (9) and the pathway. Circuitry (23) including a pair of exposed parallel plates (17, 19) detects the presence of impurities such as salt on the top surface (5). Circuitry (21) supplies a time-varying electrical current to the sensor electrode (9) at a frequency at which the apparatus (1) is relatively sensitive to impurities on the block"s surface when substantially pure precipitation is present at a frequency at which the apparatus (1) insensitive to impurities when impurities are detected. The presence of precipitation is signalled by a device (45) when the capacitive and conductive losses between the sensor electrode (a) and the pathway indicate such precipitation. </p> |
