| 摘要 |
1,169,197. Proximity detector circuits. ROBERTSHAW CONTROLS CO. Oct. 24, 1966 [Oct. 23, 1965], No.47623/66. Heading G1N. A proximity switch circuit comprises a proximity sensing capacitor CS connected in a bridge circuit with a set point capacitor CSP and a centre-tapped secondary winding of a transformer T, the bridge circuit being connected into the regenerative feedback loop of a transistor oscillator, whereby the amplitude of oscillation is modulated by the approach of a body to the sensing capacitor. In the absence of a body, the set point capacitance is greater than the sensing capacitance, giving a maximum position feedback and corresponding maximum amplitude of oscillation. A bistable trigger circuit 24 is switched at a predetermined amplitude of oscillation to energize a relay or output circuit (28). In the oscillator, transistors Q1 and Q2 have substantially identical characteristics and are connected so that the effects of their base-collector capacitances substantially cancel out. Sensing capacitor construction. One electrode of the sensing capacitor comprises the housing for the circuitry of Fig. 4 and the other electrode is a fired silver coating 50 on a glass plate 48. |
