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RGH20F incremental encoder system with RSLR linear scale


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


  • High accuracy spar scale 
  • High resolution outputs from the REF interface
  • Ultra compact readhead
  • Auto Gain Control (AGC) for excellent signal integrity
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What is RGH20F?

The RGH20F compact readhead offers reliable, high speed, open, non-contact performance with excellent immunity to dust, scratches and light oils on the scale.

The RGH20F readhead is used with the REF interface, which incorporates automatic gain control and unique self-tuning adaptive electronics. Combined with the readhead's 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 RSLR scale?

RSLR 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 RSLR scale is perfect for long-travel applications where metrology cannot be compromised.

High resolution

Using the REF interface, the RGH20F readhead is capable of resolutions up to 5 nm.


The low profile RGH20F 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.

Technical specifications

Measuring standard

RSLR: high accuracy stainless steel spar scale

Readhead size (LxWxH)

36 mm x 13.5 mm x  10.5 mm

Scale pitch

20 μm

Thermal expansion coefficient

~10.8 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 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  

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

Electrical connection

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

Power supply

5 V -5% +10%, 200 mA (unterminated)

Vibration (operating)

100 m/s² max @ 55 Hz to 2000 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 sheet

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.

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.

RGH20 optical scheme with annotations