Wire wound potentiometer

Wire wound potentiometer comprises of several rounds of wire wound around the shaft of the non-conducting material. The turns of the coil are bonded together by an adhesive. In this case the slider, connected to the body whose
displacement is to be measured, moves on the potentiometer track and it makes contacts with successive turns of the coil. In this case the wire between the two successive turns is not covered by the slider, which limits the resolution of the wire wound potentiometers. However, the larger the number of turns of the coil more is the resolution of the coil. The resolution is measured as the reciprocal of the number of turns of the coil.

The wire wound potentiometer produces a stepwise increase in resistance as the wiper moves from one turn of the wire to another, thus imposing a restriction on the resolution of the transducer. For rotational devices the resolution R can be figured out from,

R=〖360×10〗^(-3)/πnD

Where D is the diameter of the potentiometer in meters and n is the number of turns/mm.
It may be noted in this context that a higher resolution demands thinner wires which, in turn, means a higher total resistance. Thus, resolution and resistance are interdependent. Wires of nickel-chromium (nichrome), nickel-copper (constantan), silver-palladium or some other precious metals are used as resistive elements, their diameters varying between 25 and 50 µm.

To avoid surface oxidation, they are annealed in a reducing atmosphere. On the other hand, hard alloys like phosphorous-bronze, beryllium-copper or other precious metal alloys are used to construct wipers and are shaped in such a way that they slide with minimum friction and at same time maintain a firm contact with the winding.

Advantages
High Power
Heat Tolerance
Very Long Life
Low Noise