| 摘要 |
PURPOSE:To accurately measure an electric energy in the manner of eliminating the effect of an offset voltage by feeding back the output signal of a bridge switch to an intergation circuit after dividing the voltage to a half. CONSTITUTION:A load voltage is detected by an auxiliary transformer 1 and a consumption current is detected by an auxiliary current transformer 3, and the product of both amounts is calculated by a time-division multiplying circuit 5 for a pulse-width modulation, then plus and minus voltage signals eop, eon corresponding to the electric power are outputted and supplied to the bridge switch 11 of a voltage-frequency conversion circuit 7. At this time, the voltage of output signals Sm, Sn is divided to a half by means of connecting resistors 41,43 having the same resistances in series between output terminals of the bridge switch 11, and this divided voltage is supplied to an inversion input terminal of an operational amplifier circuit 15 through a resistor 45. With this arrangement, the offset voltage superimposed to the signals Sm,Sn is detected at a center point of the resistors 41,43 and feeded back to the integration circuit of the operational amplifier 15 then automatically controlled; therefore, the secular change of the offset voltage can be also eliminated. |
