A motion rate sensor for detecting the rate of movement of an article, comprising: a housing relative to which, in use, the article moves, a detection unit disposed within the housing, the detection unit including a conversion device adapted for generating detector signals caused by the motion of the article, and processing circuitry adapted for receiving said detector signals and outputting motion signals indicative of the rate of movement of the article. In embodiments, the detector signals are caused by variations in optical or light energy, in magnetic fields or radiation intensity. The variations may be caused by variations on the surface in the article, for example a random or repetitive pattern. An apparatus and method for calibrating the sensor are also disclosed, as are a system and method for determining the speed of motion of an article using the sensor.
