Gas sensor control apparatus and method
There is provided a control apparatus for a gas sensor, which has a sensor element equipped with first and second oxygen pumping cells. The sensor control apparatus is configured to drive the first oxygen pumping cell to adjust the oxygen concentration of gas under measurement, drive the second oxygen pumping cell to produce a flow of electric current according to the amount of oxygen pumped out of the oxygen concentration adjusted gas by the second oxygen pumping cell, perform specific drive control to control the amount of oxygen pumped by the second oxygen pumping cell to a predetermined level after startup of the sensor element and before the application of the drive voltage between the electrodes of the second oxygen pumping cell.
1. A control method for a gas sensor, the gas sensor comprising a sensor element equipped with first and second oxygen pumping cells to define first and second measurement chambers so that a gas under measurement first flows in the first measurement chamber and then flows from the first measurement chamber into the second measurement chamber, each of the first and second oxygen pumping cells having an oxygen ion conductor and a pair of electrodes arranged on the oxygen ion conductor, the control method comprising:
driving the first oxygen pumping cell in such a manner that the first oxygen pumping cell pumps oxygen in or out of the first measurement chamber to adjust the oxygen concentration of the gas in the first measurement chamber;
driving the second oxygen pumping cell with the application of a drive voltage between the electrodes of the second oxygen pumping cell in such a manner that the second oxygen pumping cell pumps oxygen out of the second measurement chamber to produce a flow of electric current between the electrodes of the second oxygen pumping cell in accordance with the amount of the oxygen pumped by the second oxygen pumping cell;
determining the concentration of a specific gas in the gas under measurement based on the electric current between the electrodes of the second oxygen pumping cell; and
performing specific drive control by supplying a constant current to the second oxygen pumping cell for a predetermined time period in such a manner as to control the amount of the oxygen pumped by the second oxygen pumping cell to a predetermined level after startup of the sensor element and before the application of the drive voltage between the electrodes of the second oxygen pumping cell.
2. A control apparatus for a gas sensor, the gas sensor comprising a sensor element equipped with first and second oxygen pumping cells to define first and second measurement chambers so that a gas under measurement first flows in the first measurement chamber and then flows from the first measurement chamber into the second measurement chamber, each of the first and second oxygen pumping cells having an oxygen ion conductor and a pair of electrodes arranged on the oxygen ion conductor, the control apparatus being programmed to:
drive the first oxygen pumping cell in such a manner that the first oxygen pumping cell pumps oxygen in or out of the first measurement chamber to adjust the oxygen concentration of the gas in the first measurement chamber;
drive the second oxygen pumping cell with the application of a drive voltage between the electrodes of the second oxygen pumping cell in such a manner that the second oxygen pumping cell pumps oxygen out of the second measurement chamber to produce a flow of electric current between the electrodes of the second oxygen pumping cell in accordance with the amount of the oxygen pumped by the second oxygen pumping cell;
determine the concentration of a specific gas in the gas under measurement based on the electric current between the electrodes of the second oxygen pumping cell; and
perform specific drive control by supplying a constant current to the second oxygen pumping cell for a predetermined time period in such a manner as to control the amount of the oxygen pumped by the second oxygen pumping cell to a predetermined level after startup of the sensor element and before the application of the drive voltage between the electrodes of the second oxygen pumping cell.
3. The control apparatus according to claim 2 , wherein the control apparatus is configured to read any information correlated with a temperature of the sensor element and initiate said specific drive control when the temperature of the sensor element becomes higher than or equal to a reference temperature.
4. The control apparatus according to claim 2 , wherein the control apparatus is configured to set an upper limit on the voltage between the electrodes of the second oxygen pumping cell during said specific drive control.
5. The control apparatus according to claim 4 , further comprising an operational amplifier with a noninverting input terminal, an inverting input terminal and an output terminal, the inverting input terminal and the output terminal being electrically connected to each other,
wherein the operational amplifier sets the drive voltage between the electrodes of the second oxygen pumping cell when a first input voltage is inputted to the noninverting input terminal and sets the upper limit on the voltage between the electrodes of the second oxygen pumping cell when a second input voltage higher than the first input voltage is inputted to the noninverting input terminal during said specific drive control.