Miniature multiple-function probe for OTV turbopump health monitoring

A miniature multifunction rotating machinery shaft displacement sensor designed for a turbopump health monitoring system is described. The sensor probe tip has three independent sensing electrodes running in a groove made in the shaft of the machine. One of these electrodes, situated at the tip of the sensor, measures the radial displacement of the shaft, while the two side electrodes measure the axial displacements of the sides of the groove. The displacement sensor is also used to measure speed, by providing a notch in the side of the groove facing one sensor electrode. Results obtained with experimental sensors demonstrated that multifunction capacitive sensing is practical and reduces instrumentation penetration into rotating machinery housings.