Denso Corporation

Yohei Kawaki

Eiichi Kurokawa

Toshiyuki Suzuki

Tomoo Kawase

A sensor control apparatus includes an applied voltage control circuit connected to the positive terminal of a sensor element. The applied voltage control circuit includes a reference power supply and a noninverting amplifier circuit connected to the reference power supply. An AC power supply circuit, a buffer and a current measurement resistance are connected in series to the negative terminal of the sensor element with the current measurement resistance disposed between the AC power supply circuit and the sensor element. One terminal of the current measurement resistance, which is on the side opposite to the sensor element, is held at a reference voltage (center voltage of an AC voltage generated from the AC power supply circuit). Voltage at an intermediate point between the current measurement resistance and the sensor element is inputted via a low-pass filter to the noninverting amplifier circuit of the applied voltage control circuit.

Sensor control apparatus

The gas sensor control apparatus develops a first voltage based on a first reference voltage at a negative terminal of a gas sensor device through a resistor and a second voltage based on a second reference voltage at a positive terminal of the gas sensor device. A controller samples through the resistor a sensor current, as created upon the development of the first and second voltage for measuring the concentration of gas. When the impedance of the gas sensor device is measured, the controller alternates the first voltage across the first reference voltage. The value (i.e., a zero-point) of the voltage applied to the gas sensor device when the sensor current is zero (i.e., 0 mA) depends upon the first and second reference voltages. The zero-point is corrected by regulating the second reference voltage to match an applying voltage characteristic to the gas sensor device correctly.

Gas sensor control apparatus designed to ensure accuracy of measurement in gas sensor

A gas concentration detection apparatus includes a series-connected combination of a sensor element and a resistor, with an AC voltage being applied to one of the outer terminals of that combination and with the other outer terminal being held at a fixed potential. A DC voltage signal at a level determined by an oxygen concentration that is detected by the sensor element, and an AC voltage signal at an amplitude determined by sensor element impedance and hence by the sensor element activation status, are extracted from the series-connected combination by respectively separate circuits which apply separately determined amplification factors.

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Toyota, Japan

Yohei Kawaki