| 摘要 |
A capacitive sensor may be used as a proximity detector in an obstruction warning system for road vehicles, e.g. for use when the vehicle is reversing. A digital signal processor 11 sends a sine wave through a sensor RC circuit 1, 7. A sensor plate 3 acts as one plate of a sensor capacitor 1 and the obstruction 45 acts as the other plate 5. Changes in the distance between the car 43 and the obstruction 45 result in changes in the capacitance of the sensor capacitor 1, changing the amplitude and phase of the sine wave output by the sensor RC circuit 1, 7. A reference sine wave, generated by a reference signal circuit 17, 19, 21 is subtracted from the sensor output signal in a subtractor 15. The reference signal has a phase offset from the sensor signal so that the amplitude of the difference signal is highly sensitive to changes in phase of the sensor signal. An additional signal, substantially identical to the sensor signal, is coupled to the output of the sensor RC circuit by a coupling capacitor 41. This provides a path to ground for high frequency noise without disrupting the sensor signal. |
