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RGH20F incremental encoder with RESR rotary (angle) ring


  • Readhead size: 36 x 13.5 x 10.5 mm
  • Resolutions to 5 nm
  • Speed to 5 m/s (up to 1 836 rpm depending on ring size and resolution)
  • Analogue or digital outputs
  • Low Sub-Divisional Error (SDE): typically ±0.05 µm


  • High accuracy ring
  • High resolution outputs
  • 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 RESR scale?

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

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

RESR: 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 10.5 mm

Scale pitch

20 μm

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)

1 836 rpm (5 μm resolution RGH20F with REF on 52 mm RESR)

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 and 5 m cable lengths with D-sub connectors (9 pin and 15 pin) or flying lead

Power supply

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

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 papers

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

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