Apparatus for detecting wet and icy surface conditions

摘要

Apparatus for detecting wet and icy conditions on the surface of a pathway. A block of electrically insulative material is embedded in a pathway with the top surface of the block being substantially flush with the surface of the pathway and exposed to atmospheric precipitation. A sensor electrode is positioned a predetermined distance beneath the top surface of the block and encapsulated in the block so that the accumulation of atmospheric precipitation on the top surface of the block affects the capacitance and conductance between the sensor electrode and the pathway. A time-varying electrical current having an amplitude which is substantially constant and independent of the accumulation of atmospheric precipitation on the top surface of the block is supplied to the sensor electrode. The apparatus also includes an amplifier for amplifying an electrical signal applied to a pair of input terminals thereof. One input terminal of the amplifier is commonly connected to the source of the time-varying electrical current and to the pathway in the vicinity of the sensor electrode. The sensor electrode is connected to the other input terminal of the amplifier to complete a circuit between the source of the time-varying electrical current, the sensor electrode and the amplifier, thereby applying an electrical signal to the amplifier. The amplitude of the electrical signal at the input terminals of the amplifier is substantially solely a function of the change in capacitance and conductance between the sensor electrode and the pathway as atmospheric precipitation accumulates on the top surface of the block. An amplified signal from the amplifier is supplied to a precipitation signal circuit which in response to the amplitude of the amplified signal reaching a predetermined magnitude provides an output signal indicative of the presence of atmospheric precipitation on the pathway.