Skip navigation

RGH40 incremental encoder system with RGS40-G linear scale


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


  • Proven reliability
  • Easy to install
  • Dual end of travel limit switches
  • Digital RS422 output direct from the readhead
Transparent patch for website banners

What is RGH40?

The RGH40 readhead offers all the benefits of the market proven RG4 linear 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 RGS40-G scale?

RGS40-G is a glass spar scale featuring 40 µm pitch incremental graduations in lengths up to 1 m. The spar has an accuracy of better than ±4.1 µm over a 1 m length.
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?


The RGH40 readhead is a robust and reliable encoder system with a proven pedigree ensuring low cost of ownership.

Ease of setup

With generous setup tolerances and an integral setup LED offering real-time signal feedback, the RGH40 readhead can be installed quickly and easily.

Dual limit sensing

The RGH40 readhead includes dual limit switch sensing as standard to enable dedicated signals for each end-of-axis indication. A repeatable reference or datum mark also comes as standard.

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

RGS40-G: chrome on glass spar scale

Readhead size (LxHxW)

44 mm x 27 mm x 17 mm

Scale pitch

40 μm

Thermal expansion coefficient

~8.5 μm/m/°C

Accuracy grade

±4.2 μm (1 010 mm length)

Reference mark

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

Limit switches

Dual limits

Scale length

Actual lengths: 130 mm, 180 mm, 230 mm, 280 mm, 310 mm, 510 mm, 760 mm, 1 010 mm (measuring length is actual length – 10 mm)

Maximum speed



(See data sheet for details)

Up to 6 m/s at -3 dB

Up to 10 m/s

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




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 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 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