Patent ID: 6720534
Filing Date: 2004-04-13
Classification: G01N

Abstract:
A heater control apparatus used for a gas concentration sensor which includes a gas chamber, a first cell working to pump thereinto oxygen molecules contained in gasses admitted into the gas chamber and discharge the pumped oxygen molecules, a second cell working to determine a concentration of a specified oxygen containing gas component contained in the gasses having passed through the first cell, a solid electrolyte member on which at least one of the first and second cells is disposed, and a heater heating the first and the second cells, comprising:a sensor element resistance value determining circuit working to applying one of a varying voltage and a varying current to the solid electrolyte member and measuring resulting changes in voltage appearing across the solid electrolyte member and current flowing through the solid electrolyte member to determine a resistance value of a sensor element including the solid electrolyte member; a heater control circuit controlling a power supply to the heater as a function of a difference between the resistance value determined by said sensor element resistance value determining circuit and a target resistance value; a heater power determining circuit determining a power supplied to the heater; and a correcting circuit working to determine a reference resistance value of the sensor element as a function of the power determined by said heater power determining circuit based on a predetermined fundamental relation between a power used in the heater and a resistance value of the sensor element, said correcting circuit correcting the target resistance value as a function of the reference resistance value.