| 摘要 |
PURPOSE:To distinguish a short rush current from faulty or overload current thereby to prevent a malfunction, by winding an auxiliary coil on a fixed iron core and arranging such that a movable iron core is attracted only when the current flowing through the auxiliary coil is cut off. CONSTITUTION:A fixed iron core 3 is wound with a current coil 1 and an auxiliary coil 2. The auxiliary coil 2 is connected with a resistor 5 and a switch 7 in series. Moreover, a timer circuit 6 is connected in parallel to the resistor 5. A movable iron core 4 having a load 8 is disposed at a stroke l separated from the fixed iron core 3. In operation, when a current I1 is supplied to the current coil 1, a magnetic flux phi1 is generated. In addition, owing to an induced current I2, a magnetic flux phi2 is generated having a phase 180 degrees behind that of the magnetic flux phi1. When the current I2 flows through the resistor 5, the timer 6 is actuated to measure the time elapsed, and after a predetermined time passes, the switch 7 is opened. As a result, the current phi2 becomes zero, and the total magnetic fluxes become sufficient to attract the movable iron core 4. |
