Abstract: A method for detecting a marked element on an eddy wheel in proximity to a sensor is described. The method includes the steps of accumulating sensor output signals over a selected time period. The number of sensor output signal over a first and second time period are determined. From that number an average value is calculated. A threshold value is established for the average for determining whether the marked is present. The threshold value is compared to the average value. If the average value is greater than the threshold value, an output signal is generated to indicate the presence of the mark.

Abstract: A sensor for detecting the rotation of an eddy wheel in an electric power meter is described. The sensor includes a pair of light sources arranged to focus light on the edge of the wheel, and a light detector arranged to sense reflections from the edge of the wheel caused by the light from the light sources. The light from either sensor is sufficient to trigger the detector, thereby requiring a sufficiently large interruption in the reflection, for example as caused by a mark on the edge of the eddy wheel, to interrupt the detector output. A filter is described for eliminating jitter in rotation of the eddy wheel.