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RGH20 incremental encoder system with RSLR20 linear scale


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


  • High accuracy spar scale
  • Digital RS422 output direct from the readhead
  • Compact 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 RSLR20 scale?

RSLR20 is a stainless steel spar scale featuring 20 µm pitch, which is comparable to fine pitch glass scales and offers a total accuracy (including slope and linearity) better than ±4 µm over a 5 m length. It can also be coiled for simple storage and handling yet once uncoiled behaves as a spar scale.
System designers can choose between specially formulated adhesive tape or mechanical clips to suit mounting requirements. Both mounting methods allow for independent thermal expansion to that of the substrate.

Why choose this encoder system?


With a total accuracy of ±4 μm at 20 °C over a 5 m length, the RSLR20 scale is perfect for long-travel applications where metrology cannot be compromised.

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.


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

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

High accuracy stainless steel spar scale

Readhead size (LxWxH)

36 mm x 13.5 mm x 14.8 mm

Scale pitch

20 μm

Coefficient of thermal expansion at 20 °C

10.1 ±0.2 µm/m/°C

Accuracy grade at 20 °C

±1.5 µm up to 1 m, ±2.25 µm up to 2 m, ±3 µm up to 3 m, ±4 µm up to 5 m, calibration traceable to international standards

Reference mark

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

Limit switches

Optional single limit

Scale length

20 mm to 5 000 mm

Maximum speed   

(See data sheet for details)
Up to 3 m/s at -3dB
Up to 8 m/s

Sub-Divisional Error (SDE)

Typically < ±0.15 µm

Dynamic signal control


Incremental signals   

1 Vpp (20 µm period)
Resolutions from 5 µm to 10 nm

Electrical connection

1.5 m, 3 m, 5 m cable lengths with D-type connectors (9 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/s² max @ 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

Refer to data sheets for full details.


Data sheets

Technical drawings

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