Patent ID: 7582197
Filing Date: 2009-09-01
Classification: F02D,G01N

Abstract:
1. A gas concentration measuring apparatus comprising: a gas concentration sensor equipped with a sensor element which is made of a solid electrolyte body and a pair of electrodes affixed to the solid electrolyte body; a sensor control circuit connected to the electrodes of the sensor element through a positive and a negative terminal, when a gas concentration measuring mode is entered, said sensor control circuit applying a voltage across the electrodes of the sensor element to produce a flow of electrical current through the sensor element and sampling the electrical current through a current-measuring resistor to output a sensor current signal as indicating a concentration of a gas to be measured, when an internal resistance measuring mode is entered, said sensor control circuit working to perform one of a voltage sweep mode and a current sweep mode, in the voltage sweep mode, said sensor control circuit applying a voltage to the sensor element and sweeping the applied voltage in an ac form to sample a resulting change in voltage provided by the sensor element, in the current sweep mode, said sensor control circuit supplying a current to the sensor element and sweeping the supplied current in an ac form to sample a resulting change in current provided by the sensor element, said sensor control circuit outputting one of the resulting changes in voltage and current as an internal resistance signal; and a failure monitor working to sample values of the sensor current signal before and after the sensor element is activated and a value of the internal resistance signal after the sensor element is activated, said failure monitor detecting a failure in said gas concentration sensor based on the sampled values.