Brief description of faults caused by sensor mutation

In the measurement and control system, the output signal of the sensor is affected by many factors, and mutations often occur. This mutation point value contains important fault information. Accurately capturing and distinguishing the factors that cause these mutation points is the key to sensor fault diagnosis. Most rely on the output time sequence of the sensor to diagnose the fault of the sensor, and the sudden change of the sensor output signal is attributed to the fault of the sensor.

The specific method of detecting faults is to perform wavelet transform on the input and output signals of the control system. When the wavelet function can be regarded as the first derivative of a smooth function, the sudden change point of the signal corresponds to the modulus maximum value of the wavelet transform. This detects mutation points, generates a residual sequence and analyzes the sensor failure, and considers that the mutation of the sensor output signal is caused by the sensor failure or the mutation of the system input signal. In fact, there are many reasons for the sudden change of the sensor output signal. In addition to the sudden change of the system input and the failure of the sensor itself, there are also process disturbances, actuator failures, controller failures, controlled objects and external electromagnetic field interference. In practical applications, The above-mentioned sensor fault diagnosis method has certain limitations. Often, in industrial process control, the time constant of the controlled object is relatively large and cannot respond to the high frequency components in the sudden change signal. Based on the frequency band analysis technology of wavelet transform, it discusses and analyzes the causes of sudden changes in sensor output signals, and provides a practical analysis method for fault diagnosis and performance evaluation of online sensors.

The sudden change signal output by the sensor contains very important fault information. The sudden change factor is different, and the frequency composition of the sudden change signal is different. For controlled objects with a large time constant, most of the sensor mutation signals caused by given input changes, interference changes, controller failures and actuator failures are mostly low-frequency components. Among the mutation signals caused by the controlled object failure, Generally there are only low frequency components. The sudden change signal caused by external electromagnetic field interference is generally a pulse signal, which contains low frequency components and more high frequency components. In addition to low frequency components, the sudden change signal caused by sensor deviation fault also contains a small amount of high frequency components.