Gas sensor

Abstract

A gas sensor includes a reference gas regulating device that applies a control voltage that is repetitively set to on state and off state between the reference electrode and the measurement-object gas side electrode to pump in oxygen to the periphery of the reference electrode; and a detecting device that detects the specific gas concentration in the measurement-object gas on the basis of a voltage between the reference electrode and the measurement electrode during a second period, from among a first period that is started upon setting of the control voltage to on state, during which a potential difference between the reference electrode and the measurement-object gas side electrode is large, and the second period that is started upon setting of the control voltage to off state after the potential difference falls from the first period.

What is claimed is: 
     
         1 . A gas sensor comprising:
 a layered body that is formed by stacking a plurality of oxygen ion-conductive solid electrolyte layers, and that includes a measurement-object gas flowing portion which a measurement-object gas is introduced and flowed in;   a reference electrode that is formed inside of the layered body, and that receives a reference gas introduced therein, the reference gas being used as a standard for detection of a specific gas concentration in the measurement-object gas;   a measurement electrode provided on an inner peripheral surface of the measurement-object gas flowing portion;   a measurement-object gas side electrode provided in a region of the layered body that is exposed to the measurement-object gas;   a reference gas introducing portion that introduces the reference gas to a periphery of the reference electrode;   a reference gas regulating device that applies a control voltage that is repetitively set to on state and off state between the reference electrode and the measurement-object gas side electrode to pump in oxygen to the periphery of the reference electrode; and   a detecting device that detects the specific gas concentration in the measurement-object gas on the basis of a voltage between the reference electrode and the measurement electrode during a second period, from among a first period that is started upon setting of the control voltage to on state, during which a potential difference between the reference electrode and the measurement-object gas side electrode is large, and the second period that is started upon setting of the control voltage to off state after the potential difference falls from the first period.   
     
     
         2 . The gas sensor according to  claim 1 , wherein a residual voltage DVref calculated according to the following Formula (1) is 40 mV or less,
     DV ref= V ref1 −V ref0  (1)
   (where Vref 1  is a minimum voltage [mV] between the reference electrode and the measurement-object gas side electrode in a state in which the layered body is placed in an air and in which the control voltage is repetitively set to on state and off state, and   Vref 0  is a voltage [mV] between the reference electrode and the measurement-object gas side electrode in a state in which the layered body is placed in the air and in which the control voltage is not applied.)   
     
     
         3 . The gas sensor according to  claim 2 , wherein the residual voltage DVref is 35 mV or less. 
     
     
         4 . The gas sensor according to  claim 1 , wherein the following Formula (2) is satisfied,
     T 2≥1.4851×ln( Ip 3max)−4.0296  (2)
   (where T 2  is a second time [msec] that is a length of the second period, and   Ip 3 max is a peak current [μA] flowed in the reference electrode by using the control voltage.)   
     
     
         5 . The gas sensor according to  claim 1 , wherein the following Formula (3) or Formula (4) is satisfied,
     T 2≤1.685×ln( Ip 3max)+0.9899  (3)
       T 2≤0.0011× Ip 3max+7.58  (4)
   (where T 2  is a second time [msec] that is a length of the second period,   Ip 3 max is a peak current [μA] flowed in the reference electrode by using the control voltage, and   Formula (3) is a formula used when Ip 3 max≤50 μA, and   Formula (4) is a formula used when Ip 3 max>50 μA.)