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RGH25F incremental encoder system with RGS20 linear scale


  • Readhead size: 36 x 13.5 x 10.5 mm
  • Resolutions to 5 nm
  • Speed up to 5 m/s
  • Analogue or digital outputs
  • Low Sub-Divisional Error (SDE): typically ±0.05 µm
  • Vacuum compatible version available


  • High resolution outputs from the REF interface
  • Ultra compact readhead
  • Auto Gain Control (AGC) for excellent signal integrity
  • Scale lengths available up to 50 m (>50 m special order only)
  • ‘Cut-to-length' scale flexibility
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What is RGH25F?

The RGH25F compact readhead offers reliable, high speed, open, non-contact performance with excellent immunity to dust, scratches and light oils on the scale.

The RGH25F readhead is used with the REF interface which incorporates automatic gain control and unique self-tuning adaptive electronics. Combined with filtering optics, these ensure excellent signal integrity and low Sub-Divisional Error (SDE). The REF interfaces are available with high resolution digital outputs or with industry standard 1 Vpp analogue output.

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?

High resolution

Using the REF interface, the RGH25F readhead is capable of resolutions up to 5 nm.


The low profile RGH25F readhead allows for easy integration into all but the most restricted of spaces.

Self tuning

The REF interface incorporates automatic gain control (AGC) and unique self-tuning adaptive electronics which, combined with the filtering optics, ensure excellent signal integrity, and give a low cyclic error.

Long lengths

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

Technical specifications

Measuring standard

Gold plated steel tape with protective lacquer or polyester coating

Readhead size (LxWxH)

36 mm x 13.5 mm x 10.5 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 switch

Optional single limit (select at time of order)

Scale length

Up to 50 000 mm

Maximum speed



(with REF interface):

Up to 6 m/s at -3 dB

Up to 5 m/s

Sub-Divisional Error (SDE)

Typically < ±0.05 μm

Dynamic signal control

Self-tuning active correction including Auto Offset Control (AOC), Auto Gain Control (AGC) and Auto Balance Control (ABC) for optimised performance during operation

Incremental signals



(with REF interface):

1 Vpp (20 μm period)

Resolutions from 5 μm to 5 nm

Electrical connection

1.5 m, 3 m and 5 m cable lengths with D-type connector (15 pin)

Power supply

5 V - 5%, + 10%, 200 mA maximum (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 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.

With the unique optical design of the readhead and the Auto Gain Control (AGC) and Auto Offset Control (AOC) features of the REF interface, low short-term errors are assured, typically giving less than ±0.05 μm Sub-Divisional Error (SDE).

The REF interface 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.

RG2 optical scheme with annotations

Technical drawings