| 摘要 |
PURPOSE:To make it strong against disturbance and reduce power consumption, by conducting a measurement in a condition that one end of a condutive cell is connected to a common terminal, and also by reducing number of active elements. CONSTITUTION:An output terminal of a reference AC voltage generating circuit 11 is connected to a positive-side input terminal + of a differential amplifier 12, one end of a conductivity cell 13 is connected to a common terminal Ct, and the other end is connected to a negative-side input terminal - of the differential amplifier 12. The differential amplifier 12 issues an AC signal e1, a part of which contains an information of condutivity rate, to an output terminal by an AC voltage signal e1 to be given to the input and a signal from the conductivity cell 13. And an AC signal e1 and a signal e which is from the reference AC voltage generating circuit 11 are introduced into an operation processing section 14, and by making adding or substracting process on these signals and also by turning them into DC, a signal e3 proportional to the conductivity rate is put out. It is possible, by doing so, to conduct a measurement of high reliability without being limited by measuring location and conditions, etc. |
