The sensor operation is based on the measurement of the so-called Nernst potential, which is proportional to the concentration of oxygen ions in a controlled gaseous medium.
Sensitive element of the oxygen sensor (G3/2) consists of a combination of the Nernst element and (41a) diffuse element (41b) (ion pump), which moves ions from the cathode to the anode. To improve the measurement accuracy, the oxygen concentration in the ambient air is compared. To do this, the sensor has an air channel (41 d).
The sensor provides a satisfactory measurement accuracy of ratio 1 within (0.7 < k< 4.0).
The condition for stable operation of the sensor is the constancy of temperature. To do this, the sensor has a heater that constantly maintains the temperature of the sensor at about 750'C.
The ratio X=1 corresponds to the voltage on the Nernst element U - 450 mV.
VN 9.031 Oxygen sensor circuit 48. Control circuit; 81. Exhaust gas flow; 41a. Nernst element; 41b. Ion pump; 41s. Diffusion gap; 41d. Air channel; 41s. Heater; IP. Ion pump current; uh. Heater voltage; Uref. Comparative voltage
VN 9.032 Dependence of the ion pump current on λ Signal of the ion pump (IP) IP. Ion pump current (mA)
VN 9.033 1. Inlet oxygen sensor G3/2; 2. Sensing element; 3. Top insulator; 4. Sealing filler; 5. Sensor housing; 6. Bottom insulator; 7. Outer protective tube; 8. Inner protective tube