JPS6480874A - Electronic watthour meter - Google Patents

Abstract

PURPOSE:To accurately identify even an open-phase state wherein electric energy is not measured by controlling a display means according to the open-phase signal and power failure signal of a three-phase three-wire AC power source. CONSTITUTION:An I-side open-phase signal and a III-side open-phase signal (b) from the main body part 1 of the electronic watthour meter of the three- phase three-wire AC power source are normally high-level signals and an active electric energy pulse signal (c) and a reactive electric energy pulse signal (d) supplied to the 2nd data input B of a selector 39 are displayed at a frequency of 2Hz. Further, if either of the I side and III sides enters an open-phase state, the signal (a) or (b) falls to a low level, the selector 39 selects a 1Hz signal (g), and a display part 7 displays it at a frequency of 1Hz, so that the occurrence of the open phase state is identified. Further, if the three-phase three-wire AC power source enters a power failure state and an AC off signal (f) rises to a high level, the output of a NAND circuit 35 rises to high level and a high- level AC off signal (f) is lighted and displayed.