RESR rotary (angle) encoder system

High performance, easy installation and a variety of readhead options.

Graduation accuracy to ±0.5 arc second and resolution to 0.004 arc second.

Great performance combined with outstanding value-for-money.

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RESR - 3 ringRenishaw's RESR angle encoder offers impressive performance. With graduation accuracy to ±0.5 arc second and resolution to 0.004 arc second, the RESR suits the most demanding precision applications.

RESR rings

RESR - 3 ring, no headsThe RESR ring is a one-piece stainless steel ring with graduations marked axially on the periphery. The 20 µm pitch RESR is compatible with the RGH20 and RGH35 readheads, while the 40 µm pitch RESR is compatible with the RGH34 and RGH40 readheads.

  • Graduation accuracy to ±0.5 arc second and system repeatability to 0.004 arc second
  • A wide range of diameters and line counts provide compatibility with industry standard controllers (Ø52 mm to Ø550 mm with line counts from 4,096 to 86,400)
  • Patented taper mount minimizes installation errors and simplifies integration
  • 10 mm x 10 mm small cross section ring
  • Low mass, low inertia design enhances dynamic performance
  • One piece stainless steel ring withstands vibration, mechanical and thermal shock, and thermal overload
  • For even higher acceleration and deceleration, and faster settling times, extra-low inertia 'B' section rings are also available
  • The reference mark, which offers a repeatable home position, is provided by a separate magnetic actuator
  • 20 µm pitch rings are compatible with the UHV compatible RGH20F readhead

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RGH20 readhead features and benefits

  • RGH20 + RESRCompact readhead offers industry standard digital and analogue outputs
  • Non-contact design offers high speed, reliable operation with zero friction and zero wear
  • Readhead set-up LED simplifies installation
  • Patented filtering optics guarantee excellent signal stability in conditions unsuitable for most open, optical encoders
  • The REF interface offers automatic gain control (AGC), automatic balance control (ABC) and automatic offset control (AOC) to minimize cyclic error (<±50 nm)
  • The reference mark provides a repeatable home position whilst the limit offers end of axis travel indication
  • Ultra-high vacuum compatible RGH20F versions available

Compare the RGH20 with alternative optical angle readheads.

RGH34 readhead features and benefits

RGH40 readhead features and benefits

Technical specifications

Readhead dimensions

14.8 mm x 36.0 mm x 13.5 mm (RGH20) (H x L x W)

10.5 mm x 36.0 mm x 13.5 mm (RGH20F)

  9.5 mm x 15.0 mm x 15.0 mm (RGH35)

Outputs (resolution)

RS422: 5 µm, 1 µm, 0.5 µm, 0.2 µm, 0.1 µm, 50 nm, 20 nm (RGH20F only), 10 nm (RGH20F only), 5 nm (RGH20F only).

Analogue: 1 Vpp


RGH20 - internal interpolation to 50 nm

RGH20F - REF interface (x4 to x4000) (Binary interpolation factors from x4 to x4096 available)

RGH35 - RGI34 interface (x4 to x400)

Reference markBolt on magnetic actuator
Limit switchesSingle limit (dual limits available with RGH40 and 40 µm pitch RESR)
Maximum speed2,938 rev/min (20 µm at Ø52 mm)
Ride height tolerance

0.8 ±0.08 mm

Scale types20 µm pitch (compatible with RGH20 and RGH35) and 40 µm pitch (compatible with RGH34 and RGH40) RESR rings
Vacuum compatibleYes – RGH20F and 20 µm pitch RESR

System accuracy - 20 µm pitch RESR and RGH20

Nominal outside diameter (mm)

System accuracy (arc second)

 52 5.6
 57 5.1
 75 3.9
 100 2.9
 101 2.9
 103 2.8
 104 2.8
 115 2.5
 150 1.9
 200 1.4
Nominal outside diameter (mm)

System accuracy (arc second)

 206 1.4
 209 1.4
 229 1.3
 255 1.1
 300 1.0
 350 0.8
 413 0.7
 417 0.7
 489 0.6
 550 0.5

Note: system error is graduation error plus sub-divisional error (SDE). Effects such as eccentricity influence installed performance; for application advice please contact Renishaw.

Additional resources

Accessories and external interpolation options

For further information and product options, visit the encoder product configurator.

Data sheets


3D models (step format)

Technical articles

  • White paper: The accuracy of angle encoders White paper: The accuracy of angle encoders

    Many automation systems rely on precision rotary motion, such as rotary format computer-to-plate (CTP) pre-press machines, machine tool A, B & C axes, surface mount machines and wafer handling and inspection equipment. Different applications demand different combinations of performance and features to optimise their function – some require accuracy, others repeatability, high resolution or low cyclic error for velocity loop control. Typically you would select the encoder that offers the optimum balance of specification and function, and there is a bewildering array to choose from. Yet few are capable of meeting all requirements.


Next steps

Contact us online if you require more information or you have a pricing query, or alternatively you may like to speak directly to your local Renishaw office.