Model-based validation of a DOx sensor

An optimal sensor validation (SEVA) procedure should generate a measurement uncertainty associated with any detected fault and where possible correct for the effect of the fault on the derived measurement data so that the transmitter always provides the best estimate of the underlying value of the physical variable. A dissolved oxygen sensor, often used for environmental sensing, uses a permeable membrane which might become fouled under adverse conditions. A test procedure, based on a physical model of the diffusion processes in the sensor, provides fault detection and correction capability. The theory behind the test and its application to a commercial DOx sensor made by Foxboro - the 871DO - are described. Practical results comparing data from a fouled but compensated sensor with data from a separate clean sensor show that the procedure is extremely effective.