| 摘要 |
PURPOSE:To obtain a detection circuit employing AC by calculating an impedance or an addmittance to be converted into the concentration of a gas to be measured from a voltage across sensor terminals when an alternating current of a fixed frequency is applied to a polarography type sensor and a current flowing through the sensor. CONSTITUTION:A polarography type sensor 1 is provided with a positive electrode 1b on a plate or one surface of a cylinder 1a made of an oxygen ion conductor and a negative electrode 1d on the other surface facing it. The negative electrode 1d is covered with a porous layer 1f, which controls the flow rate of oxygen flowing into the negative electrode 1d. The positive electrode 1b is covered with a porous protective layer 1e. An impedance measuring device 5 is connected to the sensor 1 and a converter 11 is connected thereto to convert the measured impedance value into the amount of current corresponding to object to be measured. In the sensor 1, an alternating current of 5Hz, for example, is applied to the electrodes 1b and 1d from a measured section 5 and measured. The converter 11 converts the current thus measured into the concentration of oxygen to be outputted. This eliminates decomposition of the solid electrolyte eventually causing aging of characteristics thereby enabling a measurement without requiring substantial time. |
