| 摘要 |
PURPOSE:To obtain a watt-hour meter equipped with a highly precise time counting device by generating one clock signal from a control circuit at the time of transition from the interruption of service of a commercial power supply to the start thereof and by synchronizing the signal with a reference period of a clock signal generated from a frequency divider which divides the frequency of the commercial power supply. CONSTITUTION:When the service of a commercial power supply is started, a frequency divider 3 starts counting from this time point as a starting point. Simultaneously when a microprocessor (MPU) 1 makes an interrupt action on the basis of one clock signal generated from a control circuit 11 immediately after the start, a time counter 8 counts the clock signal. Since a reset signal generated by the interrupt action of the MPU 1 is given at this time, a count value of the frequency divider 3 up to this time is cleared and the counting is restarted, while a switch 7 is changed over to the end on the service side. Accordingly, a clock signal of a one-second period is inputted from the frequency divider 3 to the counter 8 synchronously with the clock signal generated from the control circuit 11, and therefore no deviation occurs in the period of the clock signal even at the time point of changeover from the interruption of the service to the start thereof. |
