To achieve complete reliability of contact at the low brush pressures necessary for long life, Kelvin & Hughes Ltd. have made careful selection of materials for their precision potentiometers.

The example illustrated is a miniature sine-cosine potentiometer intended mainly for use in airborne equipment. This has a flat Corundite former wound with either 10 per cent rhodium-platinum or 20 per cent copper-platinum wire according to the resistance required. The face of the winding is swept in a circular track by brushes of platinum-gold-silver alloy wire, soldered end-on to beryllium-copper blades so that the contact area does not increase with wear. Slip rings of copper-palladium are used with platinum-gold-silver brushes.

Only 1-5/8 inch in diameter, the potentiometer provides 18’ revolution and 0.5 per cent sine law accuracy, with life expectation exceeding half a million revolutions.