Absolute magnetic rotary encoder OMR series

OMR Series Absolute Magnetic Rotary Encoder

The OMR series is a high‑precision absolute magnetic rotary encoder system, designed for industrial motion control, robotic joints, and servo feedback applications. It serves as a core feedback element for position and velocity control loops.

The encoder system operates on a non‑contact absolute measurement principle, incorporating a highly reliable safety chip and a precision dual‑track magnetic ring to ensure long‑term stability in harsh industrial environments.

Measurement Principle

The OMR uses a dual‑track magnetic disc (ring) as its measurement reference. The magnetic layer is magnetized through an elastomer layer with two tracks: the master track is magnetized with a 2 mm pole pitch (N/S alternating), while the nonius track provides the absolute reference.

The encoder integrates a high‑performance Hall‑effect sensor array to read both the master and vernier tracks. The alternating magnetic field generated by the precision magnetic ring is processed in the dedicated ASIC through signal conditioning and proprietary algorithms to determine the absolute position.

Mechanical and Electrical Design

The encoder housing is made of aluminum, with dimensions of 53 × 14 × 12.5 mm and a mounting hole spacing of 46 mm. Its compact form factor enables easy integration into space‑constrained applications.

On the electrical side, the OMR operates from a 5 V ±5% supply, drawing less than 160 mA under no‑load conditions at 25°C ambient. Absolute position is available within 300 ms at power‑up, and position updates are completed in less than 5 µs to support high‑speed real‑time control. Output signal types include differential RS422 and serial RS485, with output load capability of ±40 mA. Cable length ranges from 0.5 m up to 10 m.

Communication Interfaces

The OMR supports a wide range of industrial communication protocols for flexible integration:

• BiSS‑C (RS422), max clock: 10 MHz
• SSI (RS422), max clock: 1 MHz
• MODBUS‑RTU (RS485), max baud rate: 256 Kbps
• Tamagawa (RS485), baud rate: 2,500,000 bps

Status Indication and Diagnostics

A built‑in LED on the top of the encoder provides clear visual status feedback:

• Solid blue: Normal operation – position data valid
• Flashing blue: Warning – internal temperature exceeds 80°C
• Solid purple: Error – position data invalid (possible causes: demagnetized ring, or the encoder left and re‑entered the magnetic field during operation)
• Solid red: Error – position data invalid (possible causes: excessive air gap, no magnetic ring detected, or internal fault)
• Irregular alternating red/purple: Error – encoder is misaligned with the magnetic ring
• LED off: No power supply connected

Performance Specifications

The OMR delivers outstanding angular measurement performance:

• Resolution: 0.1 arcsecond (~0.000028°)
• Repeat accuracy: 0.005° (at 0.3 mm air gap)
• Absolute accuracy: ≤0.05°
• Maximum measuring length: 16.4 m
• Maximum operating speed:
• Magnetic ring: up to 10,000 rpm (HDA82 high‑speed version)
• Linear scale: up to 8 m/s
• Sensing gap: ≤0.6 mm, optimal at 0.3 ± 0.1 mm

Environmental Robustness

The OMR is rated IP67 for protection against dust and moisture, and operates over a temperature range of –20°C to +80°C. Its immunity to external magnetic fields is specified at 0.5 mT, ensuring reliable operation even in environments with strong stray fields from motors and other sources.

Compatible Magnetic Rings

The OMR series supports the following standard magnetic ring models (ID, OD, and height H are configurable):

With its high precision, non‑contact measurement, flexible communication interfaces, and compact mechanical design, the OMR series absolute magnetic rotary encoder is an ideal position feedback solution for industrial automation, robotics, and servo control applications.