The Evolution of Rotational Position Sensors: Moving Toward a Digital Future

The industry is undergoing a significant shift, moving away from traditional synchro and resolver-based input systems toward digital rotational position sensors. This transformation is driven by the growing demand for higher precision, efficiency, and ease of integration in various applications.

The Rise of Digital Position Sensors

Unlike synchros and resolvers, digital rotational position sensors can deliver up to 33 bits per revolution—at least from what we’ve observed so far (though there are undoubtedly even more advanced versions out there). These sensors commonly interface using the Synchronous Serial Interface (SSI), which we support through our DNx-SL-514 board.

Until recently, this board’s 32-bit support was sufficient. However, as newer sensors integrate additional data, including the number of revolutions and position within each revolution, read sizes have expanded to up to 60 bits. To keep pace with these advancements, we are enhancing our system’s capability to expand word size from 32 to 128 bits, ensuring compatibility with any high-precision sensor.

Why This Shift Is Happening

There’s a compelling reason behind the transition to digital position sensors—they are simply easier to use. Here’s why they’re gaining traction:

• Lower Power Requirements: Traditional synchros and resolvers require 26V AC at 400Hz, while digital sensors operate on a far simpler 5V power supply.
• Reduced Noise & Greater Protection: Using an RS-485 interface, digital sensors introduce significantly less noise into an installation and are better shielded against external interference.
• Energy Efficiency: The SSI master card consumes only a fraction of the power required to drive a synchro card, which demands higher voltage and current.
• Cost Considerations: While the sensor’s integrated electronics come at a somewhat higher cost, the difference isn’t prohibitive—and the benefits far outweigh the increase in price.

Breakdown: SSI Encoders vs. Synchros/Resolvers

SSI encoders and synchros/resolvers are both used for position feedback in motion control systems, but they operate very differently:

Question: Will SSI Encoders Replace Synchros/Resolvers?

In many industrial applications, yes—SSI encoders are already replacing synchros/resolvers due to:

• Easier integration with digital systems
• Higher resolution and accuracy
• Lower maintenance

However, in aerospace, defense, and harsh environments, synchros and resolvers are still preferred because:

• They are extremely rugged and reliable
• They can operate in extreme temperatures, radiation, and vibration
• They don’t rely on digital electronics that might fail in such conditions

Looking Ahead

As sensor technology advances, the industry must evolve to keep pace. Expanding our word size capability to 128 bits ensures seamless compatibility with the next generation of high-precision sensors. By embracing digital rotational position sensors, we’re not merely following trends—we’re driving innovation toward a more efficient, reliable, and scalable future in position sensing.

SSI encoders offer a viable alternative to synchros and resolvers in many modern applications, particularly where digital integration and high precision are essential. However, in legacy systems and extreme environments, synchros and resolvers continue to demonstrate their enduring value.

UEI SSI series boards, including the DNx-SL-514, offer seamless compatibility across all UEI chassis systems, from compact Cubes to expansive Racks, ensuring versatile integration. It also comes with a robust 10-year availability guarantee plus a 3-year standard hardware warranty, which can be upgraded to a full 10 years for extended peace of mind.

What are your thoughts on this shift? Have you encountered challenges or advantages in adopting digital sensors?

Let’s discuss!