| 摘要 |
PURPOSE:To improve the sensitivity of measurement by using an operational amplifier to integrate induction AC voltage and thereby dispensing with a filter for intercepting alternating current. CONSTITUTION:When a switch 31 is closed, the interception of alternating current between the shielding layer 13A of an embedded cable and earth is performed through the intermediary of a capacitor 22. And, since DC current from a DC power source 32 connected to earth flows through the intermediary of resistors 38 and 37 according to the corrosion of the layer 13A, the potential at the voltage-parting point 39 of the resisters 38 and 37 falls down. This falling DC current and the induction AC voltage through the intermediary of the layer 13A are processed by the operational amplifier OP forming an integrator 33, and thereby the variation of the insulation resistance due to the corrosion of the layer 13A is measured through direct reading with no influence of an AC component by means of a meter 34 through the intermediary of the integrator 33. Accordingly, a constitution whereform the filter prepared by using a resistor, etc for eliminating a high-region component is removed is obtained, whereby the component of alternating current is removed excellently and also the sensitivity of measurement is improved by the amplifying operation of the operational amplifier. |
