| 摘要 |
<p>A system for detecting wet and icy conditions on the surface of highways, airport runways and the like. A first capacitor is positioned on a surface the condition of which is being detected. This capacitor has first and second spaced-apart electrodes which are positioned substantially coplanar with the surface and exposed to atmospheric precipitation which affects the capacitor's dielectric and capacitance. A second capacitor having first and second spaced-apart electrodes is positioned so as not to be exposed to atmospheric precipitation. Respective out-of-phase time-varying signals are applied to the first electrodes of said capacitors and the second electrodes are commonly connected. The system further includes a conductivity sensor having first and second spaced-apart electrodes exposed to atmospheric precipitation which affects the sensor's resistance, a sensor circuit which supplies an output voltage the magnitude of which is a function of the resistance of the sensor, and a logic circuit responsive to any signal coupled to the second electrodes of the capacitors reaching a predetermined precipitation threshold magnitude and to the output voltage of the sensor circuit reaching a predetermined ice threshold magnitude to provide an output which indicates an icy surface condition.</p> |
