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RGH40 incremental encoder system with RESR40 rotary (angle) ring


  • Readhead size: 44 x 27 x 17 mm 
  • Resolutions to 50 nm 
  • Speed up to 10 m/s 
  • Analogue or digital outputs  


  • High accuracy ring
  • Taper mounting ring simplifying integration and reducing installed errors 
  • Digital RS422 output direct from the readhead 
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What is RGH40?

The RGH40 readhead offers all the benefits of the market proven RG4 rotary encoder system - generous installation tolerances and high-speed, non-contact performance with filtering optics to guarantee reliable performance over light oils, dust and scratches.

What is RESR40 scale?

RESR40 incremental angle encoder is a one-piece stainless steel ring with 40 µm 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 RGH40 readhead is a robust and reliable encoder system with a proven pedigree ensuring low cost of ownership.

High accuracy

The RESR40 ring offers impressive graduation accuracy to ±0.5 arc seconds for a variety of demanding precision applications.

Ease of setup

The RESR40's patented taper mount minimizes installation errors and simplifies integration.

Direct output

The RGH40 outputs RS422 digital resolutions from 5 µm to 50 nm direct from the readhead without the need for an additional interface.

Interface option

REE interface

  • Can be used with RGH40A 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 an improved cyclic error over the all-in-one digital readheads. 
  • Please refer to the REE datasheet for further information.

Technical specifications

Measuring standard

One-piece low profile stainless steel ring. Standard ‘A' section with tapered internal diameter or low inertia ‘B' section

Readhead size (LxHxW)

44 mm x 27 mm x 17 mm

Scale pitch

40 μm

Coefficient of thermal expansion at 20 °C15.5 ±0.5 μm/m/°C

Ring outer diameter

52 mm to 550 mm

Line count

4 096 to 43 200 (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)

±6.3 to ±0.6 arc seconds (depending on ring diameter)

Maximum speed



(See data sheet for details)

2 938 rpm at -3 dB (on 52 mm RESR)

3 687 rpm (10 μm resolution RGH40 on 52 mm RESR)

Sub-Divisional Error (SDE)

Typically < ±0.3 μm

Dynamic signal control

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

Incremental signals



(See data sheet for details of angular resolution)

1 Vpp (40 μm period)

Resolutions from 10 μm to 50 nm

Electrical connection

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

Power supply

5 V ±5%, 120 mA (typical), 175 mA (0.4 μm, 0.2 μm, 0.1 μm and 50 nm) (unterminated)

Vibration (operating)

100 m/s2max @ 55 Hz to 2 000 Hz

Shock (non-operating)

1 000 m/s2, 6 ms, ½ sine

Operating temperature

0 °C to + 55 °C



 * 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.



White paper

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

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 ±0.30 μm Sub-Divisional Error (SDE). For even lower SDE and even higher signal stability, the analogue version of the RGH40 can be connected to the REE interface which include Auto Gain Control (AGC) and Auto Offset Control (AOC) that operates at all speeds.

The RGH40 readhead features a set-up LED, which lights green when optimum installation has been achieved.

A magnetic reference mark is available with this readhead, providing a unidirectional repeatable zero position.

RGH40 optical scheme with annotations