Abstract: A current detection resistance in a sensor control device is connected to a sensor element. The current flowing in the sensor element is detected through the current detection resistance. The current detection resistance is connected to an inverting amplification circuit for outputting an air/fuel output voltage to be transferred to a microcomputer. An offset setting circuit is connected to one input terminal of an operational amplifier in the inverting amplification circuit. The offset setting circuit is comprised of a switching element, a resistance connected in series to the switching element, and two dividing voltage resistances whose common node is connected to the resistance. The offset setting circuit generates and gives an offset to the A/F output voltage. The switching element is turned ON and OFF based on an offset switching signal transferred from the microcomputer.

Abstract: 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.

Abstract: A gas concentration measuring apparatus for use in air-fuel ratio control of automotive engines is designed to determine the concentration of oxygen within a wide and a narrow range using a sensor current flowing through a sensor element. The apparatus includes an amplifier circuit equipped with an operational amplifier and a plurality of amplifying resistors and a switch. The switch is responsive to a request signal to switch a relation in electrical connection between an operational amplifier and the amplifying resistors to distribute the amplifying resistors into an input resistor and a feedback resistor for the operational amplifier to change an amplification factor of the amplifier circuit. This results in a change in resolution of measurement of the concentration of oxygen, thereby ensuring enhanced accuracy in determining the concentration of oxygen in a selected one of the narrow and wide ranges.

Abstract: A noiseless circuit structure of a gas concentration measuring apparatus is provided. The gas concentration measuring apparatus includes a control circuit and a gas sensor including a solid electrolyte body, a cell, and a heater serving to heat the solid electrolyte body up to an activation temperature. The control circuit is designed to cancel or remove electric noises arising from an on-off operation of the heater added to a sensor output.

Abstract: A gas concentration measuring system for use in air-fuel ratio control of motor vehicle engines is provided which is designed to determine the concentrations of oxygen as a function of an air-fuel ratio of a mixture supplied to the engine through a sensor element. The sensor element is activated by heat produced by an electric heater. The system works to sample the accumulated amount of energy inputted to the sensor element by the heat produced by the heater to determine whether the sensor element has been activated enough to produce an output representing an actual value of the air-fuel ratio correctly or not. Use of the accumulated amount of energy inputted to the sensor element will result in a decreased time required for such a determination as compared with the impedance of the sensor element.

Abstract: A fault detecting apparatus for a gas concentration sensor is provided. The apparatus includes a storage device and a fault detecting circuit. The storage device stores therein fault detectable conditions in which preselected different types of faults of the gas concentration sensor are allowed to be detected, respectively. The fault detecting circuit works to detect a selected one of the faults stored in said storage device. When one of the fault detectable conditions is encountered during operation of the gas concentration sensor, the fault detecting circuit initiates detection of a corresponding one of the faults based on an output of the gas concentration sensor, thereby enabling the fault detecting circuit to identify the type of one of the faults to be detected correctly.

Abstract: A sensor impedance measuring apparatus is provided which is designed to apply one of an alternating voltage swept in level to a positive and a negative side to a sensor element of a gas sensor such as an O2 sensor or an A/F sensor and sample the voltage developed at an end of the sensor element to determine the impedance of the sensor element. The determined impedance is, for example, used to control energization of a heater built in or affixed to the sensor element to control the activation of the sensor element for ensuring the accuracy in measuring the concentration of a gas.

Abstract: In a device for detecting an abnormality of a gas sensor having a detected cell in which a pair of electrodes are provided on a solid electrolyte material, a microcomputer temporarily inputs a test signal including an alternating current component to a signal line connected to the electrode and detects a response signal developing in response to the test signal. If there is no disconnection in the cell, a current corresponding to the alternating current component flows between the electrodes due to a parasitic capacity of the cell to produce the response signal. If there is a disconnection therein, the magnitude of the response signal becomes zero. Therefore, if a detection value of the response signal falls below a reference value, a decision is made that a disconnection abnormality occurs in the cell. This enables a disconnection in the gas sensor to be detected with accuracy.

Abstract: A gas concentration measuring apparatus is provided which works to measure the concentration of a gas using a gas sensor element. The apparatus also works to determine the impedance of the gas sensor element through an arithmetic circuit for use in controlling the activation or diagnosis of the gas sensor element. The arithmetic circuit uses a command signal from a sensor controller to determine a sampling time at which a change in voltage applied to the sensor element or current flowing therethrough that is a function of the impedance of the sensor element is to be sampled. This permits the impedance to be calculated accurately in a simplified manner without use of a resource such as a timer.

Abstract: A gas concentration measuring apparatus for use in air-fuel ratio control of motor vehicle engines is provided which is designed to determine the concentrations of oxygen at different resolutions within a wide and a narrow range using a first and a second sensor signal which are amplified by first and second operational amplifiers at different amplification factors. The apparatus samples values of the first sensor signal at different concentrations of oxygen to find an output characteristic error of the first operational amplifier and determines an actual concentration of oxygen to calculate an output characteristic error of the second operational amplifier using the one of the first operational amplifier and the actual concentration of oxygen. This permits values of the first and second sensor signals to be corrected so as to compensate for the output characteristics of the first and second operational amplifiers.

Abstract: A gas concentration measuring apparatus for use in air-fuel ratio control of motor vehicle engines is provided which is designed to select or determine a correction factor for an output of an A/F sensor, as produced through a sensor control circuit, for compensating for errors in circuit characteristics of the A/F sensor and/or the sensor control circuit to ensure the accuracy of measurement in the apparatus.

Abstract: A gas concentration measuring apparatus for use in air-fuel ratio control of motor vehicle engines is provided which is designed to detect and identify a cause of failure in operation of an A/F sensor. The apparatus works to apply the voltage to a sensor element and sweep it to produce a change in electrical current flowing through the sensor element for measuring the impedance of the sensor element. The apparatus samples values of the change in the current, a sensor output indicating an air-fuel ratio of mixture supplied to the engine, etc., before and/or after the sensor element is activated and uses a combination thereof to identify the cause of the failure of the A/F sensor.

Abstract: A gas concentration detecting apparatus comprises a gas concentration sensor and a gas concentration calculator. The sensor has first to third cells. A gas to be detected is introduced in a chamber and the first cell is responsible for discharging and changing oxygen from and into the chamber. The second cell detects a concentration of a specific gas component of the gas that has passed along the first cell. The third cell detects a concentration of residual oxygen in the gas that remains after discharge of the oxygen through the first cell. The calculator takes in a current acquired from the second cell measured with a voltage applied thereto and calculates the specific gas component concentration based on the current. The calculator includes plural concentration calculating means whose concentration detecting ranges are mutually different in a scale. The specific gas component concentration is calculated every concentration calculating means.

Abstract: A gas concentration measuring apparatus has a gas sensor consisting of pump, sensor, and monitor cells. The apparatus works to determine the value of voltage applied to the pump cell when a change in current produced by the monitor cell or the sensor cell changes upon a change in the voltage applied to the pump cell varies greatly and uses it to determine a control point to which the voltage applied to the pump cell is to be controlled. This keeps a gas concentration measuring accuracy free from, for example, aging of the sensor.

Abstract: A gas concentration measuring apparatus has a gas sensor including pump, sensor, and monitor cells. The apparatus works to look up a predetermined voltage-to-current relation to determine an initial value to be applied to the pump cell as a function of a current output of the pump cell, apply the initial value of the voltage to the pump cell, and to sweep it temporarily. The apparatus works to correct the initial value of the voltage as a function of a current output of the sensor cell upon the sweep of the initial value of the voltage applied to the pump cell, thereby better maintaining gas concentration measuring accuracy with respect to, for example, aging of the sensor.

Abstract: An A/F signal proportional to an oxygen concentration in the exhaust gas from an internal combustion engine is output upon application of a voltage based on an instruction from a microcomputer. At the time an element resistance is detected, a bias instruction signal Vr from the microcomputer is converted by a D/A converter 21 to an analog signal Vb. An output voltage Vc obtained by removing high frequency components from the analog signal Vb through an LPF 22 is input to a bias control circuit 40. During this time period in which the element resistance is detected, an accurate A/F signal is not output. Therefore, the A/F signal that has theretofore prevailed is held by a Sample/Hold circuit 70 to thereby prevent the use of an erroneous A/F signal. Namely, at the time of detecting the element resistance, the detected value of the oxygen concentration is prevented from becoming abnormal. As a result, an accurate A/F control can be executed using the detected element resistance.

Abstract: A heater control system is provided for controlling the temperature of a heater used to heat a solid electrolyte-made sensor element of a gas concentration sensor up to a given temperature at which the sensor element is activated to provide a correct gas concentration output for controlling a preselected variable used in, for example, an automotive air-fuel ratio control system. The heater control system measures a resistance value of the sensor element and controls an electric power supplied to the heater as a function of the resistance value. The heater control system is designed to determine a controlled variable properly used to control the heater, thereby resulting in improved controllability of a power supply to the heater and also works to minimize an error in determining the resistance of the heater.

Abstract: A heater controller designed to control the thermal energy produced by a heater under feedback control for heating a body of a gas sensor up to a desired activated temperature. The heater controller works to determine a feedback gain such a proportional or an integral gain as a function of a deviation of the temperature of the gas sensor from a target one and change it based on a condition in which the temperature of the gas sensor is changing from the target value. This ensures the stability of control of the temperature of the gas sensor regardless of a disturbance such as a change in ambient temperature and keeps the accuracy of gas measurement at a higher level.

Abstract: A gas concentration measuring apparatus which has a gas sensor designed to measure, for example, the concentrations of O2 and HOx contained in exhaust emissions of an automotive engine is provided. The apparatus includes a signal processing circuit which converts a current signal outputted from the gas sensor as a function of the concentration of either of O2 and NOx into a voltage signal. The gas sensor and the signal processing circuit are connected electrically through a conductor. The conductor has a length which is determined as a function of a level of the current signal outputted from the gas sensor. The weaker the level of the current signal is, the shorter the length of the conductor. This minimizes addition of electrical noises to the current signal outputted from the gas sensor.

Abstract: A fault detecting apparatus for a gas concentration sensor is provided. The apparatus includes a storage device and a fault detecting circuit. The storage device stores therein fault detectable conditions in which preselected different types of faults of the gas concentration sensor are allowed to be detected, respectively. The fault detecting circuit works to detect a selected one of the faults stored in said storage device. When one of the fault detectable conditions is encountered during operation of the gas concentration sensor, the fault detecting circuit initiates detection of a corresponding one of the faults based on an output of the gas concentration sensor, thereby enabling the fault detecting circuit to identify the type of one of the faults to be detected correctly.