Detection and Diagnosis of Friction of Spring-diaphragm Type Valve

A non-invasive method based on high order statistical theory for the detection and diagnosis of spring-diaphragm type valve was presented.The Non-Gaussianity Index(NGI)and the Non-Linearity Index(NLI)have been developed to detect the nonlinearity of signal,then the plot of process output(PV)and controller(OP)can be used to determine whether poor control loop performance was caused by friction.The validity of the method is confirmed by simulation.