| 摘要 |
PURPOSE:To obtain voltage which is exactly proportional to a quantity of electricity which a signal source has, from a voltage drop of a load resistance connected to the signal source having an internal resistance, by adding an operating circuit. CONSTITUTION:A current transformer and its secondary resistor are provided as a signal source 10 having an internal resistance Rs, and as for load resistances VR and Rn, VR is a variable resistor and Rn is an invariable fixed resistor in a load resistance in a setting circuit 20 of a protective relay. A detecting device for detecting a current of the signal source 10 is constituted of an adding circuit using an operational amplifier OP. A full voltage drop V1 by the resistances VR+Rn, and a divided voltage drop V2 by Rn are applied to terminals A, B, respectively, therefore, output voltage V0 becomes a result obtained by adding the input voltage V1, and the input voltage V2 multiplied by Rs/Rn, as R1=R2 and R3=Rn/Rs.R1, and when Is, Rs, VR and Rn are put in the place of said result, a result which is proportional to the quantity of electricity Is.Rs of the signal source is obtained.
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