Contactless potentiometers: Unlocking precision with magnetic sensing

In the evolving landscape of precision sensing, contactless potentiometers are quietly redefining what reliability looks like. By replacing mechanical wear points with magnetic sensing, these devices offer a frictionless alternative that is both durable and remarkably accurate.

This post offers a quick look at how contactless potentiometers work, where they are used, and why they are gaining ground.

Detecting position, movement, rotation, or angular acceleration is essential in modern control and measurement systems. Traditionally, this was done using mechanical potentiometers—a resistive strip with a sliding contact known as a wiper. As the wiper moves, it alters the resistance values, allowing the system to determine position.

Although these devices are inexpensive, they suffer from wear and tears due to friction between the strip and the wiper. This limits their reliability and shortens their lifespan, especially in harsh environments.

To address these issues, non-contact alternatives have become increasingly popular. Most rely on magnetic sensors and offer a range of advantages: higher accuracy, greater resistance to shocks, vibrations, moisture and contaminants, wider operating temperature ranges, and minimal maintenance. Most importantly, they last significantly longer, making them ideal for demanding applications where durability and precision are critical.

Where are contactless potentiometers used?

Contactless potentiometers (non-contact position sensors) are found in all sorts of machines and devices where it’s important to know how something is moving—without touching it directly. Because they do not wear out like traditional potentiometers, they are perfect for jobs that need long-lasting, reliable performance.

In factories, they help robots and machines move precisely. In cars, they track things like pedal position and steering angle. You will even find them in wind turbines, helping monitor movement to keep everything running smoothly.

They are also used in airplanes, satellites, and other high-tech systems where accuracy and reliability are absolutely critical. When precision and reliability are non-negotiable, contactless potentiometers outperform their mechanical counterparts.

What makes contactless potentiometers work

At the heart of every contactless potentiometer lies a clever interplay of magnetic fields and sensor technology that enables precise, wear-free position sensing.

Figure 1 The STHE30 series single-turn single-output contactless potentiometer employs Hall-effect technology. Source: P3 America

The contactless potentiometer shown above—like most contemporary designs—employs Hall-effect technology to sense the rotational travel of the knob. This method is favored for its reliability, long lifespan, and immunity to mechanical wear.

However, Hall-effect sensing is just one of several technologies used in contactless potentiometers. Other approaches include magneto-resistive sensing, which offers robust precision and thermal stability. Then there is inductive sensing, known for its robustness in harsh environments and suitability for high-speed applications. Next, capacitive sensing, often chosen for compact form factors, facilitates low-power designs. Finally, optical encoding provides high-resolution feedback by detecting changes in light patterns.

Ultimately, choosing the right sensing technology hinges on factors like required accuracy, environmental conditions, and mechanical limitations.

Displayed below is the SK22B model—a contactless potentiometer that operates using inductive sensing for precise, wear-free position detection.

Figure 2 The SK22B potentiometer integrates precision inductive elements to achieve contactless operation. Source: www.potentiometers.com

Contactless sensing for makers

So, contactless potentiometers—also known as non-contact rotary sensors, angle encoders, or electronic position knobs—offer precise, wear-free angular position sensing.

Something worth pointing out is that a quick pick for practical hobbyists is the AS5600—a compact, easy-to-program magnetic rotary position sensor that excels in such applications, thanks to its 12-bit resolution, low power draw, and strong immunity to stray magnetic fields.

Also keep in mind that while the AS5600 is favored for its simplicity and reliability, other magnetic position sensors—like the AS5048 or MLX90316—offer robust contactless performance for more advanced or specialized applications.

Another notable option is the MagAlpha MAQ470 automotive angle sensor, engineered to detect the absolute angular position of a permanent magnet—typically a diametrically magnetized cylindrical magnet mounted on a rotating shaft.

Figure 3 Functional blocks of the AS5600 unveil the inner workings. Source: ams OSRAM

And a bit of advice for anyone designing angle measurement systems using contactless potentiometers: success hinges on tailoring the solution to the specific demands of the application. These devices are widely used in areas like industrial automation, robotics, electronic power steering, and motor position sensing, where they monitor the angular position of rotating shafts in either on-axis or off-axis setups.

Key design considerations include shaft arrangement, air gap tolerance, required accuracy, and operating temperature range. During practical implementation, it’s crucial to account for two major sources of error—those stemming from the sensor chip itself and those introduced by the magnetic input—to ensure reliable performance and precise measurements.

A while ago, I shared an outline for weather enthusiasts to build an expandable wind vane using a readily available angle sensor module. This time, I am diving into a complementary idea: crafting a poor man’s optical contactless potentiometer/angle sensor/encoder.

The device itself is quite simple: a perforated disc rotates between infrared LEDs and phototransistors. Whenever a phototransistor is illuminated by its corresponding light sender, it becomes conductive. Naturally, you will need access to a 3D printer to fabricate the disc.

Be sure to position the phototransistors and align the holes strategically; this allows you to encode the maximum number of angular positions within minimal space. A quick reference drawing is shown below.

Figure 4 The schematic shows an optical alternative setup. Source: Author

It’s worth pointing out that this setup is particularly effective for implementing a Gray Coding system, as long as the disc is patterned with a single-track Gray Code. Developed by Frank Gray, Gray Code stands out for its elegant approach to binary representation. By ensuring that only a single bit changes between consecutive values, it streamlines logic operations and helps guard against transition errors.

That’s all for now, leaving plenty of intriguing ideas for you to ponder and inquire further. But the story does not end here—I have some deeper thoughts to share on absolute encoders, incremental encoders, rotary encoders, linear encoders, and more. Perhaps a topic for an upcoming post.

If any of these spark your curiosity, let me know—your questions and comments might just shape what comes next. Until then, stay curious, keep questioning, and do not hesitate to reach out with your thoughts.

T. K. Hareendran is a self-taught electronics enthusiast with a strong passion for innovative circuit design and hands-on technology. He develops both experimental and practical electronic projects, documenting and sharing his work to support fellow tinkerers and learners. Beyond the workbench, he dedicates time to technical writing and hardware evaluations to contribute meaningfully to the maker community.

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