| 摘要 |
A motor receives power through two or more relays connected to a power source. A switch-operated logic circuit is powered by a relay power source and connects to the relays. To start the motor, the switch is pressed, causing the logic circuit to close the relays sequentially. When all the relays are closed, the motor will start. If the motor starts before the logic circuit closes all of the relays, the motor is stopped and an indication is provided that the relays that have not yet been closed have failed. Otherwise, the motor runs until the switch is pressed again, causing the logic circuit to open the relays and stop the motor. The sequence in which the relays are closed is then changed. Each relay is alternately made the last in the closing sequence, therefore testing each relay in turn for failure.
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