The present invention is directed to the field of devices for controlling a hydrocarbon fuel burning device. In particular, the present invention is directed to a partial pressure of oxygen sensor which is inserted into an exhaust system which carries the exhaust gases from a hydrocarbon fuel burning device. The partial pressure of oxygen sensor is used with appropriate circuitry and mechanical devices associated therewith for controlling the amount of fuel which is introduced into the hydrocarbon fuel burning device. The amount of fuel being introduced into the device is a function of the amount of oxygen detected by the partial pressure of oxygen sensor in the exhaust gases flowing through the exhaust system.
Ceramic exhaust gas sensors of the electrically variable resistance type are known. For example, commonly assigned U.S. Pat. 3,893,230 by H. L. Stadler et al describes one such sensor fabricated from titania ceramic material. Also, commonly assigned U.S. Pat. 3,933,028 described such a sensor fabricated from cobalt monoxide ceramic material. Each of these sensor materials demonstrates an electrical resistance change as a function of the partial pressure of oxygen in the gaseous environment of the ceramic material when that material is located in the exhaust system of a hydrocarbon fuel burning device. The resistance changes may be measured by suitable electrodes. Each of the named sensing materials function best at an elevated temperature.
The present invention is directed to a particular structure for forming a partial pressure of oxygen sensor. The particular structure is one which provides a sensor of rugged construction, yet one which is efficient and effective in operation.