Importance

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Abstract

A lambda probe (1) is used with the measuring apparatus for monitoring residual oxygen in an exhaust gas, in which a measuring point for oxygen in a sensor (2) is connected via a diffusion gap (22) with a reaction chamber (24). During operation of the probe the reaction chamber drives a stream of oxygen I.sub.O2 along the diffusion gap by means of a controllably adjustable oxygen partial pressure p.sub.i. By means of an electro-chemical, oxygen ion pump driven by an electrical pump current I.sub.p, an oxygen partial pressure p.sub.i predetermined as a desired value is set in the reaction chamber. In this arrangement the pump current, the strength of which is proportional to the strength of the stream of oxygen driven along the diffusion gap, can be used as a measurement parameter for the partial pressure p.sub.m of the residual oxygen in the exhaust gas or its concentration. The residual oxygen can be monitored during a normal operating phase, the phase N. The lambda probe can be operated for test purposes, at times, particularly intermittently in a phase H or a phase L. In these operating phases H and L the oxygen partial pressure pi in the reaction chamber (24) adopts a largely minimum value or a largely maximum value. By means of changing between the named operating phases, by registering the pump current I.sub.p and by comparing the registered pump currents I.sub.p with empirical values, conclusions with regard to the ability of the probe to function (1) can be derived, so that if necessary, in the case of a lacking or faulty ability to function, measures can be introduced to remedy the deficiencies or to exchange the sensor (2).

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First Claim