1/f noise and its coherence as a diagnostic tool for quality assessment of potentiometers

The excess noise of different types of potentiometers has been investigated, and all showed a 1/f noise power-spectral density. Two types of conductive tracks are considered: carbon black resin type and metal-oxide glass cermet type. Also considered are different types of sliders: 1) metal-point contacts, 2) metal-line contacts and multiple-finger contacts, and 3) carbon brush contacts. The contributions of the end contacts, the stationary wiper (movable) contact, and the track have been investigated. The resistance and the noise of the stationary wiper contact are constriction dominated. Two different biasing conditions are proposed to measure either the coherence between current fluctuations or between voltage fluctuations in a potentiometer. The coherence measurement can serve as a fast diagnostic tool for the noise characterization and the quality of the movable contact in a potentiometer. Physical models are proposed to explain experimentally observed trends. Potentiometer 1/f noise is due to contact noise between grains in the track