Post-assembly testing of oxygen concentration monitoring Nernst cells, by application of a standard oxygen concentration and a constant electrode voltage

摘要

A detection device uses a Nernst cell (12) to measure an electrical potential between an electrode (16) and a reference electrode (18). The device is maintained at an operating temperature of greater than 300o C and a constant potential difference Up is applied across the measurement cell. A gas mixture (24') of known oxygen content is fed to the device and the Nernst current (IM) is recorded. Measurements are repeated at intervals t1, t2 , etc. An oxygen measurement device (10), such as may be used for monitoring an I.C. engine exhaust gas, comprises a Nernst measurement cell (12) and a pump cell (14) formed typically as a sandwich construction .The Nernst cell comprises platinum electrode layers (16,18) and solid electrolyte, e.g. yttrium oxide stabilized zirconium oxide, (20), and the pump cell comprises a solid electrolyte layer (42) between platinum electrodes (38,40), and a diffusion barrier (22). Diffusion of the oxygen through the medium (22) gives a time dependent concentration , which provides a potential difference between the measurement electrode (16) and the reference electrode (18) immersed in the reference atmosphere (30). The generated potential will be either negative or positive, and is applied to the pump cell (14) causing it to either move oxygen ions from electrode (40) to (38), or in the reverse direction; the pump current is monitored as a measure of the oxygen content relative to the reference atmosphere (30).