| 摘要 |
<p>1,142,783. Protective arrangements. A. REYROLLE & CO. Ltd. 22 April, 1966 [23 April, 1965], No. 17291/65. Heading H2K. A protective arrangement includes a switching circuit which operates at a predetermined instantaneous value of a rectified or unrectified alternating input signal and resets at a substantially lower value, this circuit supplying pulses to an accumulating circuit which has a reset time exceeding its response time so that it may respond to one pulse or to a series of pulses. The arrangement may be used for undervoltage protection or as shown for overcurrent protection. In this arrangement, the switching circuit comprises a current transformer 10 and a transistor trigger circuit having a transistor 20 with its base-emitter circuit connected across a bridge circuit formed by resistors 15, 16, 18 and a Zener diode 17. When this diode conducts the bridge is sufficiently unbalanced to cause the transistor 20 to conduct which renders a transistor 22 conducting. A further transistor 25 ceases to conduct and so removes a short circuit from the accumulating circuit formed by a relay coil 30 of appreciable inductance and a shunt diode 32. The resetting of the switching circuit occurs at a lower value as, when the transistor 25 is cut out, the voltage across the current-fed bridge circuit rises. In Fig. 3 (not shown) further transistors provide a feed-back and cause the resetting of the switching circuit at a lower value and the accumulating circuit includes a capacitor which is charged by the pulses. In another arrangement, Fig. 2 (not shown), both the switching and accumulating circuits include reed relays.</p> |
