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RGH22 incremental encoder system with RGS20 linear scale


  • Readhead size: 44 x 27 x 16 mm
  • Resolutions to 50 nm
  • Speed up to 10 m/s
  • Analogue or digital outputs
  • Low Sub-Divisional Error (SDE): typically ±0.15 µm


  • Proven reliability
  • Digital RS422 output direct from the readhead
  • Dual end of travel limit switches
  • Scale lengths available up to 50 m (>50 m special order only)
  • ‘Cut-to-length' scale flexibility

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What is RGH22?

The RGH22 readhead offers reliable, high speed, open, non-contact performance with excellent immunity to dust, scratches and light oils on the scale. The RGH22 also benefits from Renishaw's integral readhead set-up LED which simplifies installation and monitors signal condition during operation.

What is RGS20 scale?

RGS20 is a tape scale manufactured from a thin flexible steel strip, featuring a 20 µm pitch, which is gold plated to give high reflectivity and corrosion resistance. It may be mounted using adhesive backing tape, to most engineering materials, including metals, ceramics and composites. Secured to the substrate with scale end-clamps, RGS20 is mastered to the substrate and will match the substrate's thermal expansion. The scale is supplied on a reel and can be cut to suit any axis length up to 50 m.

Why choose this encoder system?


The RGH22 readhead with RGS20 scale is a robust and reliable encoder system with a proven pedigree ensuring low cost of ownership.

Dual limit sensing

The RGH22 readhead comes with single or dual limit sensing as standard. The limits enable dedicated signals for each end-of-axis indication. A repeatable reference or datum mark also comes as standard.

Direct output

The RGH22 outputs RS422 digital resolutions from 5 µm to 50 nm direct from the readhead without the need for an additional interface.

Long lengths

The RGS20 tape scale is available in lengths up to 50 m (contact Renishaw to discuss longer lengths).

Interface option

REE interface

  • Can be used with the RGH22A and B variants only.
  • 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

Gold plated steel tape with protective lacquer or polyester coating

Readhead size (LxWxH)

44 mm x 27mm x 16 mm

Scale pitch

20 μm

Coefficient of thermal expansion

Matched to substrate material when scale ends are fixed with end clamps

Accuracy grade

±15 μm/m (±3 μm/m when 2-point compensation is applied)

Reference mark

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

Limit switches

Dual or single limits (select at time of order)

Scale length

Up to 50 000 mm

Maximum speed



(See data sheet for details)

Up to 4 m/s at -3 dB

Up to 10 m/s

Sub-Divisional Error (SDE)

Typically < ±0.15 μm

Dynamic signal control

DC light servo provides simple Auto Gain Control (AGC) function to optimise signal level

Incremental signals



1 Vpp, 12 μA (20 μm period)

Resolutions from 5 μm to 50 nm

Electrical connection

0.5 m, 1 m, 1.5 m, 2 m, 3 m and 5 m cable lengths with D-type connector (15 pin), circular plug (9 and 12 pin), in-line connector (16 pin) or flying lead

Power supply

5 V ±5%, 120 mA (typical), 200 mA (0.1 μm and 50 nm resolutions) (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



Refer to data sheets for full details.


Technical drawings

How it works

Within the readhead, an infra-red LED emits light onto the angled scale graduations where it is directed back 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 RGH22 can be connected to the REE interface, which include Auto Gain Control (AGC) and Auto Offset Control (AOC) that operates at all speeds.

The RGH22 readhead features a set-up LED, which lights green when optimum installation has been achieved.

Reference mark and dual limits are available with this readhead. The reference mark provides a repeatable home or zero position, whilst the limits are used as end of travel indicators.

RG2 optical scheme with annotations