| 摘要 |
A circuit control device which combines the functions of a current sensor, a time-delay circuit, an undervoltage sensor and a locking device in such a manner that, once tripping has occurred, the device must be deliberately reset or restored. The current sensor has a coil which surrounds two reed switches, the reed elements of each of the switches running at right angles to those of the other switch, for reasons of vibration resistance. The coil is thus surrounded by a magnetic screen in order to screen off a portion of the leakage flux from the main relay coil. The time-delay circuit has a programmable unijunction transistor which compares a constant voltage from a voltage-divider network with the rising voltage on a capacitor. The undervoltage sensor has a second programmable unijunction transistor which compares the voltage of the DC voltage source with the constant voltage of a zener diode. In each case, the cathode of the programmable unijunction transistor is connected to the gate of an SCR (thyristor) which energises the trip coil of the locking relay when it is pulsed to "ON", which locking relay for its part opens the main relay. This also closes a further set of contacts in the locking relay, which activates a visual "tripped" display device. The device also has a reset coil in order to close the locking relay again, an override switch for energising the main relay coil irrespective of the status of the locking relay, and an energy storage capacitor for supplying power to the time-delay circuit even when the DC voltage source falls to a value which is too low to do this.
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