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RGH20 incremental encoder with RESR20 rotary (angle) ring


  • Readhead size: 36 x 13.5 x 14.8 mm
  • Resolutions to 10 nm
  • Speed up to 8 m/s (up to 2 938 rpm depending on ring size and resolution)
  • Analogue or digital outputs
  • Low Sub-Divisional Error (SDE): typically ±0.15 µm


  • High accuracy ring
  • Taper mounting ring simplifying integration and reducing installed errors
  • Compact readhead
  • Digital RS422 output direct from the readhead
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What is RGH20?

The RGH20 compact readhead offers reliable, high speed, open, non-contact performance with excellent immunity to dust, scratches and light oils on the scale. The RGH20 also benefits from Renishaw's integral readhead set-up LED which simplifies installation and monitors signal condition during operation.

What is RESR20 scale?

RESR20 is a one-piece stainless steel ring with 20 µm pitch graduations marked directly on the periphery. Two versions are available in a wide range of sizes (Ø52 mm to Ø550 mm).‘A' section rings, which offer an impressive installed accuracy, feature a taper mount system which reduce the need for highly toleranced machined parts and eliminate eccentricity. ‘B' section thin rings, which are low inertia and mass, are also available. Both 'A' and 'B' section rings 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?


The RESR20 ring offers impressive graduation accuracy to ±0.5 arc seconds for a variety of demanding precision applications.

Ease of setup

The RESR20's patented taper mount minimizes installation errors and simplifies integration.


The low profile RGH20 readhead allows for easy integration into all but the most restricted of spaces.

Direct output

The RGH20 outputs RS422 digital resolutions from 5 µm to 10 nm direct from the readhead without the need for an additional interface.

Interface option

REE interface

  • Can only be used with the RGH20B variant.
  • The REE accepts industry standard 1 Vpp analogue signals which can be interpolated and output as digital RS422 resolution. REE interface
  • Incorporating automatic gain control (AGC) and unique self-tuning adaptive electronics, the REE, combined with the filtering optics of the readhead, ensures excellent signal integrity, and gives improved cyclic error over the all-in-one digital readheads.
  • Please refer to the REE datasheet for further information.

Technical specifications

Measuring standard

One-piece low profile stainless steel ring. Standard ‘A' section with tapered internal diameter or low inertia ‘B' section

Readhead size (LxWxH)

36 mm x 13.5 mm x 14.8 mm

Scale pitch

20 μm

Coefficient of thermal expansion at 20 °C15.5 ±0.5 μm/m/°C

Ring outer diameter

52 mm to 550 mm

Line count

8 192 to 86 400 (depending on ring size)

Reference mark

Uni-directionally repeatable to 1 unit of resolution with magnetic actuator


Graduation accuracy

System accuracy

±4 to ±0.4 arc seconds (depending on ring diameter)

±5.6 to ±0.5 arc seconds (depending on ring diameter)

Maximum speed



(See data sheet for details)

1 652 rpm at -3 dB (RGH20 1 Vpp on 52 mm RESR)

2 938 rpm (5 μm resolution RGH20 on 52 mm RESR)

Sub-Divisional Error (SDE)

Typically < ±0.15 μm

Dynamic signal control


Incremental signals



(See data sheet for details of angular resolution)

1 Vpp (20 μm period)

Resolutions from 5 μm to 10 nm

Electrical connection

1.5 m, 3 m and 5 m cable lengths with D-type connectors (9 pin and 15 pin) or flying lead (unterminated)

Power supply

5 V ± 5%, 90 mA (RGH20D, X and Z),120 mA (RGH20W, Y, H, I and O), 110 mA (RGH20B) (unterminated)

Vibration (operating)

100 m/s2max @ 55 Hz to 2 000 Hz

Shock (non-operating)

1 000 m/s2, 6 ms, ½ sine

Operating temperature

0 °C to +55 °C


Readhead: IP40

Interface: IP20

*System accuracy is graduation error plus SDE. Graduation accuracy is the maximum difference between the angle measured by a single readhead and the true rotation of the encoder as graduated. Application disturbances such as eccentricity are not included.

Refer to data sheets for full details.



Data sheets

White paper

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

How it works

Within the readhead, an infra-red LED emits light laterally onto a scale with reflective and non-reflective areas. The light is directed back off the reflective areas through a transparent phase grating.

This produces sinusoidal interference fringes at the detection plane within the readhead. The optical scheme averages the contributions from many scale graduations and effectively filters out signals not matching the scale period. This ensures signal stability even when the scale is contaminated or slightly damaged.

Low short-term errors are assured by the unique optical design, typically giving less than ±0.15 μm Sub-Divisional Error (SDE). For even lower SDE and even higher signal stability, the analogue version of the RGH20 can be connected to the REE interface, which include Auto Gain Control (AGC) and Auto Offset Control (AOC) that operates at all speeds.

The RGH20 readhead features a set-up LED, which lights green when optimum installation has been achieved.

A reference mark or a single limit are available with this readhead. The reference mark provides a repeatable home or zero position, whilst the limit is used as an end of travel indicator.

RGH20 optical scheme with annotations