Detecting the blockage of the sensing lines of a differential-pressure flow sensor in a dynamic process using wavelet transform techniques

The blockage of the sensing lines of a differentialpressure (DP) flow sensor has been found to be the main cause of a malfunction of a flow measurement system in many industrial applications. In this paper, the blockage of the sensing lines under dynamic process conditions is investigated using wavelet transform techniques. The results obtained show that the blockage in a fast changing process is only detectable when the severity of the blockage is over 90%. This outcome differs from that when the sensor operates under a slow varying process. The main reason resulting in the discrepancy between slow and fast varying processes is that a process with high flow rates produces more noise energy in the output of the sensor than a process with low flow rates does. This means that the noise energy generated by the blockage of the sensor under low flow-rate conditions is indistinguishable with that from the output of the sensor working under the sensor normal operating conditions but a process with high flow rates.