When and How to Utilize Multi-Turn Encoders

Multi-turn rotary encoders are precision electromechanical sensors designed to measure, not only the angular position of a shaft within a single revolution (0° to 360°), but also the cumulative number of complete rotations. Unlike single-turn encoders, which reset their output with each revolution, multi-turn encoders provide both the absolute angular position and the total rotation count, enabling accurate position feedback across extended motion ranges.

In advanced motion control applications, capturing the shaft angle for just one 360° cycle is insufficient for reliable system monitoring. When rotational motion is mechanically coupled to linear displacement, gear trains, or large-scale equipment, tracking total revolutions becomes essential. Multi-turn encoders address this need by delivering continuous absolute position data, ensuring precise synchronization and control in complex electromechanical systems. This article will discuss multi-turn encoders in more detail, including how they work, where they can be used, and additional integration considerations.

Multi-turn encoder functionality and advantages

While it may seem feasible to track full shaft rotations in software by monitoring when a single-turn encoder rolls over from 359° to 0°, this approach introduces serious reliability challenges. Missed samples, power interruptions, communication glitches, or even vibration-induced noise can desynchronize the turn count. Rapid reversals near the 0°/360° boundary often further confuse rollover detection logic, leading to cumulative errors. Even with extensive filtering and algorithm tuning, software-based solutions remain vulnerable to accuracy loss.

Multi-turn absolute encoders address these challenges at the hardware level by integrating two critical capabilities: fine angular resolution within a single revolution and a built-in revolution counter for tracking complete shaft turns. The angular measurement is typically handled by capacitive, magnetic, or optical sensing technologies, while the revolution counter updates in synchronization with the angle data. This combination provides a true absolute multi-turn position, delivering robust and error-free feedback without reliance on external rollover logic.

The revolution counter itself can be implemented in several ways. Mechanical encoders employ gear-based systems, magnetic designs often use Wiegand wire pulse energy to register turns, and digital implementations rely on continuous electrical power. The latter typically requires careful system design to maintain power continuity—commonly through backup batteries or software safeguards—to preserve the turn count during interruptions.

How to handle multi-turn encoders at startup

A key design challenge with multi-turn encoders is managing power-up resets, since losing the stored turn count can compromise absolute position data. Several engineering strategies are commonly employed to mitigate this:

• Home or Limit Switch Reference – Upon startup, the system drives the mechanism to a predefined reference point and reinitializes the encoder’s position.
• Persisting the Last Known Value – If a host controller or non-volatile memory is available, the system can store the last recorded angle and revolution count before shutdown. After restart, these values are reapplied, provided the shaft has not moved during downtime.
• Mechanical Shaft Locking – In planned shutdowns or ultra-low power states, the shaft can be physically locked to prevent motion. The stored encoder value is then valid upon power-up, enabling seamless restoration. This method is particularly useful in portable or battery-powered systems.
• System-Level Reinitialization – For applications where losing a few turns is tolerable, the system may simply reset and recalibrate at startup using external sensors or safe default states. This reduces complexity but is only viable in non-critical position feedback applications.

For applications where losing revolution count during a power interruption is unacceptable, integrating a battery backup offers one of the most dependable solutions. Instead of relying on external recalibration methods or auxiliary sensors, this approach ensures that the encoder remains continuously powered through both brief and extended outages.

From a power-consumption standpoint, this is where technology choice becomes important. Capacitive encoders, such as Same Sky’s AMT series, typically operate at only ~80 mW, making them highly efficient for embedded and battery-powered designs. Their efficiency minimizes the drain on backup energy storage, enabling long-duration support without excessive battery capacity.

By contrast, magnetic encoders usually draw between 150 to 500 mW, while optical encoders often require 200 mW to over 1 W in high-resolution or LED-based systems. This efficiency advantage makes capacitive encoders an attractive option in power-constrained environments where every milliwatt is critical.

Figure 1: Common power consumption by encoder technology. (Image source: Same Sky)

Application examples that utilize multi-turn encoders

Here are a few common real-world scenarios where single-turn feedback just isn’t enough, and multi-turn encoders are needed:

• Gear- or Belt-Reduced Drives – When a motor completes multiple revolutions for every output shaft rotation (e.g., a 10:1 ratio), tracking only the final angle is inadequate. The system must account for all intermediate turns to maintain positional accuracy.
• Ballscrews and Leadscrews – Each shaft rotation corresponds to a fixed linear distance. Missing turns directly translates into linear position errors, making multi-turn tracking critical for precision positioning.
• Rack and Pinion Mechanisms – Continuous linear travel is generated from rotational input. Accurate feedback requires counting every rotation to calculate the true distance traveled.
• Rotary Axes in Robotics and Automation – Joints, turrets, and rotating platforms often exceed a single revolution. Without multi-turn feedback, systems risk motion errors and even collisions during operation.

From a general standpoint, a motion control system might benefit from a multi-turn encoder if the application has the following requirements:

• Extended Position Tracking – Systems that must monitor shaft movement beyond 360°.
• Rotary-to-Linear Conversion – Mechanism drives where each revolution corresponds to precise linear travel.
• High Gear Ratios – Gear- or belt-driven systems where motor revolutions far exceed output shaft motion.
• Absolute Accuracy With Minimal Filtering – Applications that cannot tolerate cumulative errors from software rollover detection.
• Streamlined Startup Logic – Designs that benefit from simpler, more reliable initialization after power-up.

Same Sky’s AMT absolute encoder family includes compact multi-turn models with SPI and RS-485 digital interfaces. Engineered for embedded motion systems, they deliver low power consumption, modular mounting flexibility, and straightforward communication—making them ideal where absolute multi-turn tracking is required. Proper management of power-up resets ensures uninterrupted accuracy across operating cycles.

While the exact communication protocol varies, most make it simple to read both angular position and turn count using a small number of bytes or commands. The commands for Same Sky’s AMT encoders are documented in their respective datasheets.

Conclusion

Multi-turn encoders streamline motion control by internally managing revolution tracking, eliminating the need for complex rollover logic or extensive software filtering. This built-in capability ensures accurate position data across extended ranges of motion, making them an indispensable component for engineers developing reliable and scalable automation systems.

Same Sky’s AMT absolute multi-turn encoders further enhance design flexibility, supporting motor shaft diameters from 2 mm to 5/8 inch (15.875 mm). This wide mechanical compatibility allows integration into a broad spectrum of motor platforms, providing robust position sensing without additional customization.