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 τ 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 τ. The measurement uncertainty associated with both normal and corrected measurements is examined