| 摘要 |
PCT No. PCT/GB87/00064 Sec. 371 Date Sep. 12, 1988 Sec. 102(e) Date Sep. 12, 1988 PCT Filed Jan. 30, 1987 PCT Pub. No. WO87/04792 PCT Pub. Date Aug. 13, 1987.An apparatus for detecting contamination of a capacitive sensor, comprising a guard electrode surrounding a portion of the sensor, and a circuit for supplying an excitation signal to the sensor and an identical excitation signal to the guard electrode. The circuit periodically isolates the guard electrode from the excitation signal, and detects the difference between the sensor output when the guard electrode is supplied with the excitation signal and when the guard electrode is isolated from the excitation, the detected difference being a function of the contamination of the guard electrode. |
