Sensor validation and outlier detection using fuzzy limits

In a continuous industrial process, the accuracy and reliabitity of process and analytical measurements create the basis for control system performance and ultimately for product uniformity. Validation of measured values is the key and a prerequisite to guarantee reliable measurements for process control. This application introduces the use of standard deviation and density function-based absolute limits. Limits are used to cut off outliers and weigh the reliability of the on-line measurement against more reliable, but seldom made, laboratory analysis. Absolute limits are accomplished with constant or adaptively updating fuzzy limits. The adaptive fuzzy limits are recursively updated in real time when a new measured value and reference analysis become available.