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.
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.
1) Supply voltage or GND (It’s possible to switch the connection and choose between increasing or decreasing
2) Supply voltage or GND.
3) Output signal.
4) Supply track.
6) Resistive track.
7) Output track.
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 are usually a combination of wire-wound and conductive plastic, the coil is coated with a conductive ink.
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’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 both linear and rotary potentiometric sensors, and 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.