| abstract |
The change in capacitance of a sensor is linearly proportional to ice thickness provided that the ice thickness is significantly less than the distance between the conductive electrodes. By employing sensors with different electrodes, the sensitivity to ice may be traded off against the ability to measure greater ice thickness. A sensor with small spacing between electrodes will exhibit a large change in capacitance when covered by a thin layer of ice, however, the capacitance change will be linear only for very thin layers of ice. A sensor with greater spacing between electrodes is less sensitive to ice accretion but has a correspondingly greater ice thickness measurement range. Accordingly, sensor (55) is relatively sensitive and is employed to determine whether or not ice or water is present. This is accomplished by circuit (60) determining whether the measured capacitance is above or below a threshold value. In one particular embodiment, the capacitance of sensor (55) without ice or water present was found to be 400 pF, while the capacitance with ice or water present was found to be 440 pF. |