Online validation of the measurement uncertainty of a sensor using wavelettransforms

The measurement uncertainty of a sensor as a measure of its accuracy is nor mally derived through static analysis. Conventionally, uncertainty analysis is conducted during, the design and development stage of a sensor to selec t appropriate components and measurement techniques. as well as interpretin g its experimental data. The demand for quality assurance by measurement is now increasing. It is therefore desirable to develop a means of assessing the measurement uncertainty of a sensor during its operation on a process p lant. A new method using wavelet transforms for the validation of the measu rement uncertainty is proposed. Analytical results show that the process va riable being measured by the sensor can be separated from a noisy raw senso r signal using its wavelet transforms, provided that the process variable i s represented in terms of a limited-degree polynomial function. Unlike the conventional approach to uncertainty Calculation. which requires, 'average' or 'typical' values substituted for parameters which may vary, the propose d method uses only the latest output of the sensor regardless of the variat ions of the parameters. and thus can be applied on an online continuous bas is. Experimental results obtained from a differential-pressure flow sensor on a water flow test rig confirm the effectiveness of the proposed method.