WATT-HOUR METER

PURPOSE:To automate switching of resolution in response to the integrated value by using a digital signal processor having the floating point type calculating function. CONSTITUTION:Voltage V and current i are normalized by input circuits 11, 12 then converted into digital signals by A/D converters 21, 22, and the digital signals Vn, in are fed to a digital signal processor(DSP) 30. The DSP 30 calculates Pn=VnXin to obtain the instantaneous power value Pn and integrates it (wh=SIGMAPn) to obtain the integrated power value wh. The calculated result by the DSP 30 is transferred to a CPU 40 in the floating point type. The CPU 40 determines the position of the decimal point in response to the value of the inputted integrated power data and the number of display digits of an indicator 50 and displays the value on the indicator 50. The display can be automatically switched to widen the dynamic range and increase resolution.