Potentiometer Technology

What is a Potentiometer?

A potentiometer is an adjustable voltage divider, the basic components in all potentiometers are a resistive element/track and a sliding contact called wiper, some potentiometers are also equipped with an output signal track and on others is the wiper connected directly to the output signal. The wiper short circuit the resistive track and signal track and the potentiometer divide the supply voltage proportional to the wiper position along the sensor. There is a wide range of different potentiometers, but there are three main technologies; wire-wound, conductive plastic and hybrids.

To the left is a schematic drawing of a potentiometer with system load RL R1 is the resistance ahead of the wiper and R2 is the resistance after the wiper.

Wire-wound Potentiometer

The resistive element in a wire-wound potentiometer is a coil of very thin wire, bonded together by an adhesive. Wire-wound potentiometers are most common in rotary sensors. The wiper is mounted on the sensor shaft and slides along the coil, the output signal is proportional to the wipers position on the coil. As the resistive element is made of wires will the output signal be in discrete steps, how coarse or fine the resolution is depends on the quality of the coil.

Conductive Plastic Potentiometer

A conductive plastic sensor element consists of a PCB and a resistive ink. The ink is screened to the PCB and the surface of the hardened ink is very precise and smooth. This enables very high resolution compared to wire-wound potentiometers, and the lifetime is long due to the low friction between sensor element and wiper. Some potentiometers have linearized sensor elements, a technique that offers very high linearity.

Above is a drawing of a sensor element in a conductive plastic potentiometer.

Supply voltage or GND (It’s possible to switch the connection and choose between increasing or decreasing
output).
Supply voltage or GND.
Output signal.
Supply track.
PCB.
Resistive track.
Output track.
Wiper.

Conductive plastic potentiometers are similar to wire-wound ones, except that the pickup moves on an element of conductive plastic instead of a coil. The conductive plastic element consists of a substrate and a resistive epoxy. The conductive plastic is applied to a substrate that most commonly consists of FR4 or similar material. When the plastic has hardened, a very smooth and fine resistive surface is created on which the sensor will travel. This surface provides a better continuous output signal than can be obtained from previously mentioned wire-wound potentiometers. The service life also increases as the sensor and the resistive element are not subjected to the same amount of stress. With a method called “trimming” or “linearizing”, a conductive plastic potentiometer can get a very good linearity.

Membrane Potentiometer

Membrane potentiometer is a special version of conductive plastic. Instead of parallel sensor tracks is the tracks stacked on top each other, separated by a spacer. The sensor tracks are connected by a wiper that push the tracks together. Membrane potentiometers are very thin (down to 0.5 mm) and used in applications where there is limited space.

Hybrid Potentiometer

Hybrid potentiometer are usually a combination of wire-wound and conductive plastic, the coil is coated with a conductive ink.

“Non-contact” Potentiometer

Non-contact potentiometer is when the wiper is not mechanically connected to the transducer shaft. A magnet is mounted to the shaft and the magnet pulls the wiper. So, the wiper is non-contact to the shaft, but the wiper is still in contact with the sensor element.

Advantages with a Potentiometer

Regal Component’s potentiometers are based on conductive plastic and the special version called membrane potentiometer. Conductive plastic has an accurate and durable output and long lifetime. There is linear and rotary potentiometric sensors, and the conductive plastic is used in both.

Temperature resilient. Operating temperature of -40°C… +125°C. There are high-temp versions up to 200°C.
EMC combability.
Very high resolution.
Priceworthy.