Abstract: A circuit is utilized for measuring a diffusion-limited current which flows through a diffusion-limited current element in proportion to an oxygen concentration which includes an output resistor connected in series with the element, a differential amplifier having a first input connected to a reference voltage supply source, a second input connected to ground, an output connected to the output resistor, and a feedback resistor connected between the first input of the differential amplifier and a point between the element and the output resistor, so that a bias voltage applied across the element is kept constant.

Abstract: An oxygen analyzing method for determining a positive or negative oxygen concentration of a measurement gas which changes between oxidizing and reducing atmospheres. The method uses a sensing element having an oxygen sensing cell wherein an electromotive force is induced between its measuring and reference electrodes according to the principle of an oxygen concentration cell. The atmosphere adjacent to the measuring electrode is controlled by controlling a pumping current to be applied to an oxygen pumping cell such that the electromotive force induced in the sensing cell is maintained at a predetermined level. A heater is provided to heat the sensing and pumping cells, to maintain their operating temperature within a range of 700.degree.-960.degree. C. The pumping current, or a signal to control the pumping current, is converted into an oxygen concentration signal whose level is held within one of a positive range and a negative range.