| 摘要 |
PURPOSE:To allow a passing electric railcar to detect the alteration of a power source frequency in a short period of time by comparing a specific comparison voltage preset for each power source frequency with the output voltage of a D/A converter, and outputting a frequency detection signal from a window comparator when a coincidence is obtained. CONSTITUTION:The signal of a zero-cross comparator 8 of a power source voltage is formed in a rectangular wave, the outputs of first and second AND gates 11, 12 which are input together with the output of a 15kHz pulse oscillator 13 are respectively input to first and second counters 14, 15, the outputs are respectively applied to first and second D/A converters 18, 19, and converted to analog voltages. The outputs of the converters 18, 19 are connected to a high priority circuit 20, higher voltage input is output as it is, and applied to first and second window comparators 21, 22. The window comparators 21, 22 output signals corresponding to the power source voltage of 50 and 60Hz to allow a passing electric railcar to substantially momentarily determine the power source frequency. |
