Volume 25, Issue 2 (March 1997)
The Nonvibrating Kelvin Probe and Its Application for Monitoring Surface Wear
This paper reports on the design and development of the nonvibrating Kelvin probe that could be used as a noncontact sensor for tribological damage. This device detects surface charge through temporal variation in the electron work function of a material. Experiments are performed to demonstrate the operation of the probe on a rotating aluminum shaft. The probe, made of lead, is placed adjacent (<0.5-mm distance) to the shaft. The two surfaces, which are electrically connected, form a capacitor. Benchmark experiments on the variation of the work function with changes in surface chemistry were performed by coating a segment along the shaft circumference with a colloidal silver paint. As the shaft rotated, the probe senses changes in the contact potential difference with the shaft surface, due to the compositional variation. The temporal variation in the contact potential difference induces a current in an external electrical circuit. This current is amplified and converted to a voltage signal. The magnitude of the signal decreases asymptotically with the electrode-shaft distance and increases linearly with the rotational frequency, as expected. These results are consistent with the theoretical. Preliminary tests to detect mechanical surface damage, using the probe, were also done. These results show that the Kelvin probe can distinguish geometrical features on the surface.