| 摘要 |
An electronic metering system having self-test capabilities. First and second analog signals are produced which are indicative of the voltage and current, respectively, carried on a line. The first analog signal is modulated to provide a digital signal changeable between two levels at predetermined clock times. The ratio of duration of the signal at one level to that of the second level is proportional to the line voltage. The modulated signal and second analog signal are multiplied together to produce a product signal which represents power carried on the line in either direction. The product signal is converted to a train of pulses, with each pulse representing a predetermined amount of power. Self-test capability is provided wherein a test signal is momentarily substituted for the first analog signal, with the test signal corresponding to a line voltage of zero magnitude. A comparator is provided for confirming that the converted product signal corresponds to zero power carried on the line in either direction when the test signal is applied. If the converted signal differs from zero power more than a predetermined amount, an error signal is produced indicating a meter system malfunction. |
