Displacement Transducers

A typical displacement transducer is a shaft-sensing proximity probe. A proximity probe is a non-contacting transducer mounted on a stationary mechanical structure to measure the distance between the probe tip and the shaft surface. A proximity probe has signal response between DC and 1.5 kHz, as well as flat phase response in the operational range. You typically use proximity probes in lower frequency measurements.

You can use a proximity probe to perform machine monitoring and protection measurements for DUTs with fluid film bearings. Because the flexible fluid film bearing and heavy housing usually generate low-frequency, external vibration responses, an accelerometer or a velocity transducer cannot measure the vibration effectively. By measuring the relative displacement of the shaft, a permanently mounted proximity probe can measure the vibration through shaft motion. You also can use proximity probes for functions such as radial or axial position monitoring and rotational speed calculation. A proximity probe is a common type of tachometer.

A proximity probe is susceptible to shaft surface scratches, circular irregularity, shaft bow, and variations in electrical properties. Accurate displacement signal measurements require compensation to remove these signal errors. The NI Sound and Vibration Measurement Suite provides Weighting and Filtering VIs and Reference Data Processing VIs to perform compensation to remove these signal errors.