Monitoring Cavitation in Centrifugal Pumps using a Noninvasive Capacitance Sensor

Cavitation in centrifugal pumps damages pump components, reduces delivery performance and
consumes additional energy. This paper presents a novel non-invasive method based on capacitance
measurement techniques for detecting and diagnosing cavitation in a centrifugal pump. Two cylindrical metal plates placed on the external wall of non-conductive pipe in the discharge line constitute the two electrodes of the capacitive sensor. The electrode plates and the pipe wall can be modeled electrically using a RLC circuit. The frequency shift of the circuit at resonance due to dielectric changes of different air to water ratios is measured to quantify the level of cavitation. Test results have shown that the frequency shifts can be as high as 200kHz with only a small amount of bubbles induced in the flow. The frequency shifts exhibit a nonlinear increasing behavior but give a good indication of the onset of cavitation and different levels of cavitation activity.