User control arrangement for glass ceramic cooker hob, has rotatable knob held in position over ceramic plate by magnetic force, and pattern on underside of knob used to determine setting position in conjunction with e.g. optical sensor

摘要

A rotatable knob (12) is removably held over a glass ceramic plate (14) by means of a magnet (24) on its underside which reacts with the magnetic field produced by magnets (26) below the plate. The angular position of the knob is determined by means of a printed strip (22) with progressively-changing reflectivity on the underside of the rotatable knob in conjunction with optical sensors (20) below the ceramic plate. Alternatively, the strip may be in the form of a conductive pattern and capacitive sensors are employed.