| 摘要 |
PURPOSE:to enable highly accurate measurement to be always performed without mutual interference even though a current sensing resistor having poor performance is used, by connecting a resistace compensating circuit between the current sensing resistor and an A-D cnverter. CONSTITUTION:A measured current I which is sent from a current source 2 to be measured is converted to an analog voltage Vs=RsI by the sensing resistor 3. Said voltage Vs is further converted to an analog voltage V0=Rb.Rg.Rs.I/(Ra. Rf)-(Rg.Vz/Re)+Voff by the resistance compensating circuit 8. In this equation, the first term is span adjusting term by which the resistace Rs of the resistor 3 is equivalently increased or decreased, and the second term is the zero adjusting term for the offset voltage V0ff in the third term for antiphase operational amplifiers 9 and 10. The outout voltage V0 from the compensating circuit 8 is displayed on a display 7 via the A-D converter 4, a code cnverter 5, and a driver 6. In this constitution, even though the sensing the sensing resistor, whose accuracy is poor and the resistance value is low, is used, its value, which is low, is equivalently compensated to the highly accurate value. |
