| 摘要 |
PURPOSE:To prevent an output from having a floating potential by a method wherein, when variations in resistance is measured by permitting a constant-current to flow into a resistor to obtain output voltage rough addition and subtraction, a specially constructed 3-input adder-subtracter is used. CONSTITUTION:A resistor Rt is a temperature sensing resistor. A conductive wire L1 is connected to an input terminal A and the first input terminal 1 of the 3-input adder-substracter AD4 via the contact point SA of a change-over switch, while L2 and L3 are connected to the second input terminal 2 and the third terminal 3, respectively. The AD4 contains 2 operational amplifiers OP1, OP2, and the positive phase input end of the OP1 is connected to the input terminal 2. The negative- phase input end of the OP1 is connected to the common potential P through the R1, to the output end of the OP1 through the R2, while the positive-phase input of the OP2 is connected to the input terminal 1 and the negative phase input end is connected to the output end of OP1 through the R3, to the output end of the OP2 through the R4 and to the third input terminal 3 through the R5. By adopting proper values for R1-R5, E05=(1+R4/R3)DELTARt.i as the output of the OP2 can be obtained. |
