Introduction - Basic Potentiometer Theory • Resistors • Building Potentiometers • Modern Variable Resistive Devices • Applications Modes • The Parts of a Potentiometer • Resistive Elements • Cermet • Conductive Plastic • Hybrid Elements • Terminations • Contacts • Electrical Parameters • Total Resistance • Minimum Resistance • End Resistance • Contact Resistance • Contact Resistance Variation • Equivalent Noise Resistance • Output Smoothness • Adjustability • Temperature Coefficient • Resolution • Conformity • Linearity • Power Rating • Summary of Electrical Parameters • Useful Terms

Resistive Element

The heart of any potentiometer is the resistive element, since it affects all other parts. There are two general types of resistive elements: wirewound and non-wirewound. The non-wirewound type includes cermet and conductive plastic, as well as a hybrid element which combines wirewound with conductive plastic.

Let's examine each type.


Wirewound Elements

Resistance wire is commonly made from one of three alloys:

  • nickel-chromium
  • nickel-copper
  • platinum-gold
Nickel-chromium is the most common one due to its availability in many different diameters, and its fine performance under temperature changes (called its temperature coefficient),

For accuracy and economy, high-speed automatic machinery is used to wind the wire onto a long mandrel or into a continual helix. The mandrel or the helix is then cut into elements of the proper size.

In terms of advantages, wirewound elements offer good stability of total resistance over time and temperature changes. Additionally, these elements offer low noise in the static state, high power capabilities, and good operational life.

In terms of limitations, wirewound elements lack a smooth adjustment of output, due to the wiper's jumping from one wire to the next one. In systems sensitive to such steps, care should be taken to select a potentiometer with resolution good enough to avoid difficulty.


Non-Wirewound Elements

Variable resistive devices that are not made with resistance wire are actually categorized by the industry and the military as non-wirewound. As you are aware, these devices use cermet, conductive plastic, and a hybrid material. We will now briefly discuss each one.