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RESOLUTE™ ETR absolute encoder system with REXA rotary (angle) ring


  • Protocol available: BiSS®
  • Readhead size: 36 x 16.5 x 17.2 mm
  • Resolutions to 32 bits/rev
  • Speed to 8 500 rev/min
  • Operating temperature range: -40 °C to +80 °C
  • Installed accuracy to ±1 arc second
  • Side cable outlet version available


  • Thick cross-section ring
  • Excellent motion control performance
  • Wide set-up tolerances
  • Less than 10 nm RMS jitter for improved positional stability
  • ±40 nm Sub-Divisional Error for smooth velocity control

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RESOLUTE ETR (Extended Temperature Range) is a true absolute, fine pitch optical encoder system that has excellent dirt immunity, and an impressive specification that breaks new ground in position feedback. It is the world's first absolute encoder capable of 32-bit resolution at 8 500 rev/min.
This brings all the benefits of the revolutionary RESOLUTE absolute, fine pitch angle encoder to harsh, low-temperature applications. With operation guaranteed down to -40 °C (-40 °F) in non-condensing environments, RESOLUTE ETR is ideally suited for use in demanding applications such as telescopes, scientific research and defence and aerospace.

The Queen's Award for Enterprise: Innovation 2015


Winner of a Queen's Award for Enterprise 2015 in the Innovation category

What is REXA ring?

REXA is a one-piece stainless steel ring with 30 µm pitch absolute graduations marked directly on the periphery. Its larger cross-section allows for the reduction in all installation errors apart from eccentricity, which is easily corrected using the average result of two Resolute readheads. Featuring total installed accuracy up to ±1 arc second, zero coupling losses, and exceptional repeatability.
REXA is available in a range of sizes (Ø52 mm to Ø417 mm), all of which have a large internal diameter for flexible integration. The non-contact format eliminates backlash, shaft wind-up (torsion) and other mechanical hysteresis errors that are inherent in traditional enclosed encoders.

Why choose this encoder system?

ETR (Extended Temperature Range)

With solid stainless steel scales and high vibration resistance, the RESOLUTE ETR absolute encoder has been designed to withstand the physical punishment of harsh environments, yet still offer outstanding metrology, exceptionally high speeds and excellent reliability on rotary axes.

Excellent motion control performance

RESOLUTE's industry-leading performance is the result of a sophisticated, reliable and innovative method of operation. Crucially, the system uses a single track non-repeating “bar code” scale format with a nominal pitch of 30 µm. With its sophisticated optical design the RESOLUTE readhead captures a near-instantaneous image of this scale which, when analysed, allows a unique position to be identified at speeds of up to 100 m/s. The system allows position to be determined with resolution as small as 1 nanometre (1 billionth of a metre) and with low noise (jitter below 10 nm RMS) and SDE (Sub-Divisional Error, the error within a scale period) of just ±40 nm. This provides encoder feedback of superior fidelity, to ensure smoother velocity control and rock-solid positional stability.

Wide set-up tolerances

RESOLUTE does not follow the conventional technique of using dual tracks side-by-side (one incremental, one absolute) which inherently suffers de-phasing problems when small amounts of angular misalignment are introduced. Instead, this absolute encoder features a single track, optical absolute scale, combining both the absolute position and embedded phase information into one single code. This technology provides RESOLUTE with far wider set-up tolerances (yaw tolerance ±0.5°) for quick and easy installation and superior long-term reliability, even if the motion axes settle or move over time. To further aid installation and diagnostics, there is an integral set-up LED on the readhead.

ProtocolDescriptionData sheetCompatible products

Renishaw supports BiSS-C (unidirectional) open protocol for absolute encoders. BiSS is a high-speed serial protocol, perfect for dynamic axes that require high acceleration, smooth velocity control, excellent bi-directional repeatability and rock-solid positional stability.
RESOLUTE with BiSS is available in both linear and rotary (angle) encoder versions, compatible with a wide range of industry-standard controllers, drives, DROs and PC counter cards.


BiSS compatible product page

Technical specifications

Measuring standard

REXA: one-piece ultra high accuracy absolute coded stainless steel ring

Readhead size (LxWxH)

36 mm x 16.5 mm x 17.2 mm

Scale pitch

Nominal 30 μm

Ring outer diameter

52 mm to 417 mm

Total installed accuracy (with 2 readheads)

(≥100 mm diameter) ±1 arc second

(75 mm diameter) ±1.5 arc seconds

(≤57 mm diameter) ±2 arc seconds

Maximum speed

(See data sheet for details)

8 500 rpm (on 52 mm ring)




BiSS-C: 18-bit, 26-bit and 32-bit

Sub-Divisional Error (SDE)

±40 nm

Electrical connection

0.5 m to 10 m cable lengths with D-type connectors (9 pin or 15 pin), flying lead

Power supply

5 V ±10%, 250 mA @ 5 V (terminated)

Vibration (operating)

300 m/s2  max @ 55 Hz to 2 000 Hz

Shock (non-operating)

1 000 m/s2, 6 ms, ½  sine

Operating temperature

-40 °C to +80 °C



Refer to data sheets for full details.

Other protocols are continually being added.


Data sheets

White papers

Technical drawings

How it works

RESOLUTE communicates bi-directionally in purely serial format, using a variety of industry-standard protocols, of both proprietary and open standard. 

RESOLUTE™ encoder optical scheme with annotations

The process begins...

The controller initiates operation by sending a demand message to the readhead, instructing it to capture the absolute position on the linear or rotary scale at that instant. The head responds by flashing a high-power LED source to illuminate the scale. The flash duration is as brief as 100 ns to minimise image blur on moving axes. Crucially its timing is controlled within a few nanoseconds to preserve the relationship between demanded and reported position, one of the essential features that makes RESOLUTE ideally suited to very high specification motion systems. 



Single track scale

The scale is essentially a single track of full-width contrasting lines, based on a nominal period of 30 µm. The absence of multiple parallel tracks gives important immunity from yaw errors and much more lateral tolerance in head position.

Image acquisition

The scale is imaged, via an aspheric lens which minimises distortion, onto a custom detector array designed specifically for RESOLUTE. The optical arrangement, with a folded illumination path but direct imaging, is highly compact yet stable thus assuring the fidelity essential for excellent metrology.

Data decoding and analysis

Once captured by the detector, the image is transferred via an analogue-to-digital converter (ADC) to a powerful Digital Signal Processor (DSP). Specially developed algorithms then obtain a true absolute, but relatively coarse position from the code embedded in the scale. This process is checked, and corrections are made by further algorithms in the DSP which exploit redundancy and intentional restrictions in the scale code. Meanwhile other routines calculate a very high resolution fine position, which is then combined with the coarse position to provide a truly absolute and very high resolution location.

Final checks and data output

After final error checking procedures this information is uploaded in the appropriate protocol to the controller as a pure serial word representing position to within 1 nm. Protection against electrical noise disturbance is provided by addition of a Cyclic Redundancy Check (CRC). The entire process can take as little as a few micro seconds and be repeated up to 25 000 times per second. By a variety of techniques, including adjusting the light flash duration to the axis speed, this performance is achieved at up to 100 m/s while, crucially, preserving exceptionally low positional jitter at lower operating speeds.

And the result is...

An encoder with generous installation tolerances: RESOLUTE allows ±0.5° in yaw, pitch and roll and an impressive ±150 µm in rideheight. Meanwhile the generous optical footprint and advanced error correcting procedures confer excellent immunity to optical contamination, both particulate and greasy smears. All this while maintaining 1 nm resolution at 100 m/s: RESOLUTE is the answer to the toughest absolute challenge.