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% 0 <br /> APPENDIX I <br /> The lambda oxygen sensor is an exhaust gas probe which senses the <br /> oxygen level in the exhaust stream. The symbol for lambda, A, is some- <br /> times used as in A sensors. <br /> The output voltage of the sensor is a function of the equivalence <br /> ratio (called A) of the air-fuel mixture used for combustion. The <br /> equivalence ratio is defined by: <br /> A = actual air/fuel ratio <br /> stoichiometric air/fuel ratio <br /> The important features of the lambda oxygen sensor are: Probe <br /> type, yttrium partially stabilized zirconium dioxide ceramic, platinum <br /> inner electrodes, outer electrodes in the form of a .combined thin film- <br /> thick film composite, graphite packing as a contact medium and seal, <br /> silicone protection cap over the end of the sensor to act as electrical <br /> insulation and protection against water. 2 <br /> The physio-chemical stability of the outer electrode and the <br /> graphite seal packing along with the temperature resistance of the <br /> silicone protection cap limit the upper temperature range (16000F) the <br /> sensor can withstand to ensure functional capability over extended periods. <br /> At lower temperature ranges (750oF and lower) a reduction in the sensor <br /> signal and a rapid increase in response time will be observed. This occurs <br /> because the resistance of the zirconium dioxide ceramic increases consider- <br /> ably while the catalytic activity of the electrode drops rapidly. The A/F <br /> ratio will have to be manually adjusted during start-up to allow the engine <br /> to reach the correct temperature range for operation. Z <br /> As the sensor ages there is a drop in performance. Aging has three <br /> contributing factors: <br /> (A) Excessive temperature at the engine exhaust gas tip <br /> (in excess of 16000F) . Operation at these temperatures <br /> over a long time period leads to the outer protective <br /> layer splitting and the thin-film electrode being <br /> destroyed. <br /> (B) Excessive deposits of oil and oil ashes which form a <br /> hard glaze at low temperatures (7500F) around the <br /> sensor tip. This hard glaze reduces the control <br /> efficiency of the sensor. <br /> (C) Excessive lead content in the fuel will lead to de- <br /> terioration of the sensor. 2 <br /> See Figures 3 and 4. <br /> 2 <br /> Gruber and Wiedenmann, Three Years Experience With The Lambda Sensor In <br /> Automotive Control Systems <br /> C/26 <br />