| 摘要 |
A circuit control device combining the functions of a current sensor, a time delay circuit, an undervoltage sensor, and a lockout such that, once tripped, the device must be reset intentionally. The current sensor includes a coil (16a) surrounding two reed switches (18, 20), the reed elements (18a, 20a) of each of which being perpendicular to those of the other for vibration resistance. The coil is then surrounded by a magnetic shield (28) in order to shield out some of the leakage flux from the main relay coil (14c). The time delay circuit includes a PUT (Q1) which compares a steady voltage from a voltage divider network with the increasing voltage across a capacitor (C3). The undervoltage sensor includes a second PUT (Q3) which compares the voltage of the DC source (10) with the steady voltage across a zener diode (D5). In each case the cathode of the PUT is connected to the gate of an SCR (Q2) which, when gated "ON," energizes the trip coil (24c) of the latching relay (24), which in turn opens the main relay (14). This also closes another set of contacts (24e, 24f) in the latching relay, which activates a visual "tripped" indicator. The device also includes a reset coil (24d) to reclose the latching relay, an override switch (SW3) to energize the main relay coil regardless of the status of the latching relay, and an energy-storing capacitor (C2) to power the time delay circuit even when the DC source voltage drops too low to do so.
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