| 摘要 |
PURPOSE:To prevent an unnecessary breaker from operating by delaying the output of a protection relay having a watchdog function for resetting the operation of a microcomputer when the microcomputer runs away until the microcomputer is reset. CONSTITUTION:A microcomputer 1 intermittently outputs a negative pulse therefrom to a watchdog WD circuit 2 during normal operation. The circuit 2 outputs a level '1' to the microcomputer 1 during its period. When the microcomputer 1 runs away to erase an intermittent negative pulse, the circuit 2 outputs a level '0' to the microcomputer 1 as a reset signal. A protection output such as a trip signal to be output from the microcomputer 1 is output to an output circuit 4 through a delay circuit 3 based on the reset signal. The delay time is set to a value longer than time by WD function until the microcomputer 1 is reset. Thus, an erroneously protective operation can be effectively prevented. |
