| 摘要 |
A starter comprising a contactor with an overcurrent relay provides an appropriate cooling interval for each of multiple classes of a load, such as a motor. An analog equivalent of a digital I2t value calculated by a microcomputer in the overload relay is maintained by an external capacitor. When the microcomputer loses power following a trip, the capacitor discharges through a resistor at a rate selected to mimic cooling of the associated class of the load. Restart of the load is prevented until the appropriate interval, represented by the time required for the voltage on the capacitor to decay to a common reset value, has expired. The capacitor is charged to a voltage proportional to the I2t trip value for the particular class of the load, which for all classes is below the forward drop of the clamping diodes on the microcomputer inputs to prevent discontinuities in the timing.
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