Development and Characterization of a Non-Intrusive Sensor to Measure Wear in Centrifugal Pumps

A magnetic sensor is designed and fabricated that allows for impeller blade wear measurement while a centrifugal pump is in operation. The sensor can be installed on existing pumps and does not require structural modification. Over time, as the pump impeller erodes, the gap between the impeller and the pump side plate increases from an unworn width of 0.65 to 2.50 mm, the maximum allowable wear on the testbed pump used for experimental validation. The extent of the impeller wear is determined by measuring over time the change in the reluctance of a magnetic circuit passing through the eroding area. The sensor flux guide mechanism has a relative magnetic permeability of 10000. Flux through the circuit is driven by an inductive coil excited with a 1.0 V AC voltage signal at 70 Hz. As wear occurs, the impeller gap grows and the total reluctance of the magnetic circuit increases, which causes the peak inductance of the coil to drop. Trial data is collected at sampling frequencies up to 500 kHz and then assessed in the frequency domain using fast Fourier transform (FFT). The amplitude of the FFT signal at the pump's rotational frequency is then considered to estimate wear. Sampling data for 1 s at 500 kHz, the sensor demonstrates a maximum signal-to-noise ratio of 17.8 dB with an average sensitivity of 0.022 mV/mm and a resolution of 0.38 mm.