Fouling detection and compensation in Clark-type DOx sensors

Clark-type dissolved oxygen (DO) sensors are used in process control and environmental monitoring applications. A common fault affecting the accuracy of DO sensor measurements is fouling: the build-up of surface agents on the membrane of the sensor. This paper outlines a technique to detect and compensate for DO sensor fouling, and hence make these instruments more robust and reliable. The technique uses an accurate model of the sensor's transient response to provide a value of the oxygen transfer time /spl tau/ in the membrane. This new value of transfer time is compared with the initial unfouled value and the measurement is compensated by a factor related to the fouling-induced changes in /spl tau/. The measurement uncertainty associated with both normal and corrected measurements is examined.