Patent ID: 9683959
Date: 2017-06-20
CPC Classifications: G01N

Claim:
1. A method for setting a temperature rising profile for increasing a temperature of a sensor element formed of an oxygen-ion conductive solid electrolyte, the sensor element being included in a gas sensor and including at least one internal space into which a measurement gas is introduced, an electrochemical pumping cell formed of a measuring electrode disposed in one of the at least one internal space, a pump electrode disposed in a portion different from the at least one internal space, and the solid electrolyte, and a heater for heating the sensor element, the gas sensor identifying a concentration of a predetermined gas component of the measurement gas based on a pump current through the electrochemical pumping cell, the temperature rising profile indicating a change in an increased temperature set relative to a temperature rising time when the heater increases the temperature of the sensor element in activation of the gas sensor, said method comprising: repeating a rapid temperature rising by the heater, for each of a plurality of the sensor elements having a temperature increased to a predetermined temperature for profile setting by the heater, while changing a temperature rising rate until a crack occurs; Weibull plotting a failure rate that is a cumulative frequency, at which cracks occur in the plurality of sensor elements in the rapid temperature rising, for the predetermined temperature for profile setting using the temperature rising rate as a distribution parameter; identifying, as a temperature-rising-rate upper limit, a temperature rising rate at which a failure rate is 1 ppm from the results of the Weibull plotting; determining, based on the temperature-rising-rate upper limit for a plurality of temperatures for profile setting, a temperature-rise upper limit curve indicating a change in the temperature-rising-rate upper limit relative to an increased temperature, the plurality of temperatures for profile setting differing from each other and including a temperature equal to or higher than an operating temperature of the sensor element; and determining, as an appropriate function, the temperature rising profile in a range in which a temperature rising rate at an appropriate temperature does not exceed values on the temperature-rising-rate upper limit curve for the temperature.