| 摘要 |
<p>A capacitive sensor (1) comprises a central electrode (2), an outer electrode (3), an insulator (4), and a backboard (5) on which is mounted electronics (6) to measure changes in capacitance when the sensor (1) is placed near a film (12), this change providing, through suitable calibration, a measure of the film's thickness. Pressurised air is supplied through inlet port (10) and flows, via chamber (9), through ports (8) to produce a layer of air (11) between the sensor (1) and film (12). This keeps the film (12) and sensor (1) apart, so that no damage is done to the film (11) or electrodes (2, 3) through contact with one another, whilst keeping the separation small and preventing relative movement and so unwanted changes in capacitance. The outer electrode (3) may comprise inner and outer skins (13, 14) (see Fig. 2) which define a passage (15) for the pressurised air, so that the air, which may contain oil and water pollutants unless filtered, does not need to pass through chamber (9) and contact the electronics (6).</p> |
