| 摘要 |
PURPOSE:To detect stably a very small change in interface potential corresponding to an ion concn. with high accuracy by operating a sensor with constant current while a liquid to be tested is maintained at specified potential. CONSTITUTION:The gate part 24 of a semiconductor ion sensor 23 sensitive with specific ion is immersed together with a reference electrode 25 into a liquid 22 to be tested and a constant voltage source 26 is connected to the electrode 25 to maintain the potential of the liquid 22 at a prescribed value. A constant voltage source 28 is connected via a reference resistance 27 between the drain D and source S of the sensor 23 to apply the specified voltage to drive the sensor 23 in the satd. region to said sensor. A potential difference between both terminals of the resistance 27 is detected by a potential control circuit 29 and the potential of the source S of the sensor 23 is so controlled by the circuit 29 that said potential difference attains a prescribed value, i.e., the drain current attains the predetermined set value. The change in the interface potential occurring in the ion concn. generated in the gate part is thus detected as a change in the source potential and the change is measured by an electrometer 30, by which the ion concn. is determined. |
