Polarographic oxygen sensor, particularly for combustion exhaust gases

Claim 1

A polarographic oxygen sensor, to measure the concentration of oxygen in gases, especially exhaust gases from a combustion process, having a metal housing (25); a closed solid electrolyte tubular body (12) sealingly secured to the housing; a reference electrode (18) located in the inside of the solid electrolyte body (12); a gas measuring electrode (15) located at the outside of the solid electrolyte body (12); means (5,25,31) applying a bias voltage, having a value in the range of about 1/2 to 11/2 volts, across said electrodes (15,18), to cause a current to flow, the value of said current depending upon the reaction, with said measuring electrode (15), of the oxygen in the gas reacting said measuring electrode (15); means (7) providing a signal representative of the value of said current flow; a protective sleeve (38), essentially solid throughout its length except for an opening (41) formed therein, sealingly secured to the metal housing (25) and surrounding the tubular solid electrolyte body (12); wherein, to facilitate economical manufacturing, said protective sleeve (38) includes a diffusion resistance zone (43/1, 43/2), which can be constructed separately from said electrolyte body (12) and said electrodes (15,18), across said opening (41) which is gas-permeable for oxygen molecules and forms a diffusion resistance element, which sufficiently throttles migration of oxygen molecules to the measuring electrode (15) on the solid electrolyte body (12) to control the speed of the consequent reaction and hence, the value of the current which flows, and thereby assure that the sensor operates under diffusion-limited-current conditions, and wherein, to increase response speed of the sensor, the protective sleeve is tubular and surrounds the solid electrolyte body with a small but finite space (39") therebetween defined by grooves, striations, or a roughened surface, sufficient to allow for vibration and to permit permeation of oxygen molecules, passing to the inside of the protective sleeve, through said diffusion resistance element (43/1, 43/2) and along at least a portion of the measuring electrode (15) on the surface of the solid electrolyte body (12).