| 摘要 |
<p>1,142,202. Automatic control systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 1, 1966 [April 12, 1965], No. 15494/65. Heading G3R. The normally-open contacts RCO of a relay RC (which may be used to control a variable) are cycled on and off at a predetermined rate by means of a transistor T3 which varies the relay coil current between its energizing and drop-off values according to the charge and discharge of a capacitor C2 produced by the opening and closing of further relay contacts RC1 operable simultaneously with the contacts RCO. Such opening and closing of the contacts RC1 alternately cuts off and makes conductive a transistor T2 whose base is additionally supplied with an A. C. signal voltage derived from a bridge B, transistor T1 and capacitor C1, so that the "on" and "off" times of the relay contacts are varied in accordance with the magnitude and sense of the signal, the circuit parameters being chosen so that the signal is ineffective when the emitter voltage of transistor T2 is changing positively. The contacts RCO may control an electric furnace whose temperature is sensed by a resistance thermometer or thermistor connected in the bridge B. The contacts RC1 may be replaced by an electronic switching means deriving control signals from the voltage across the relay coil RC. The various time constants of the circuit and the impedance of the transformer winding W2 are chosen so that members T3, RC operate with a snap-action.</p> |
