Abstract: A capacitive proximity sensor comprising an emitter electrode (104) capacitively coupled to receive an electrode (102). A first active guard electrode (110), driven by the output of a unity gain amplifier (108), is provided in respect of the receive electrode (102), to shield parts thereof not facing a potential obstacle (122), and a grounded shield (126) is provided in respect of the emitter electrode (104) to shield parts thereof not facing a potential obstacle (122). A second active guard electrode (103) is provided between the emitter and receiver electrodes (104, 102), just behind the cover (106), which is also driven by the output of the amplifier (108). The second active guard electrode (103) acts to block shortened electric field lines (124) between the emitter and receiver electrodes (104, 102), thereby improving accuracy and reliability of the sensor.

Abstract: A capacitive proximity sensor for use in object and position sensing and/or position control in respect of a swing arm of a medical imaging system. The sensor comprises, within a cover (18), an emitter electrode (10) and a sense electrode (9) both of which are formed by spraying or otherwise coating or painting a layer of conductive material on the inner surface of the cover (18). A carrier plate (30) is mounted within the cover (18), at a distance therefrom, on which are provided an active guard electrode (13) in respect of the sense electrode (9) and a grounded shield member (15) in respect of the emitter electrode (10). As there is virtually no gap between the sense electrode (9) and the cover (18), the sensor is less sensitive to the effects of material changes caused by environmental changes in temperature and/or humidity, for example.