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RGH45 incremental encoder system with RTLR40 linear scale


  • Readhead size: 44 x 27 x 17 mm
  • Resolutions to 0.1 µm
  • Speed up to 10 m/s
  • Analogue or digital outputs


  • Easy to install
  • Revolutionary FASTRACK™ track system
  • Digital RS422 output direct from the readhead
  • Dual end of travel limit switches
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What is RGH45?

The RGH45 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 RTLR40 scale?

RTLR40 is a low profile stainless steel tape scale featuring a 40 µm pitch. Accurate to ±15 µm/m and in lengths up to 10 metres. Two mounting options are available, both allow independent thermal expansion and tape scale convenience. 
RTLR40 can be used with the revolutionary FASTRACK™ scale carrier system. This system allows a track to be laid quickly and easily with no need for fixing holes. A sacrificial spacer is removed and the tape scale is then fed into the track.
RTLR40-S is laid onto the substrate with self-adhesive backing tape. The self-adhesive is formulated in such a way that it allows for independent scale expansion to that of the substrate.
To complete the installation, both types of scale are clamped at one point to provide a datum position.

Why choose this encoder system?

Revolutionary track system

Renishaw's unique FASTRACK mounting system comprises two miniature guide rails fixed with self-adhesive backing tape and is designed for applications that demand high accuracy, near-zero thermal hysteresis and easily removable scale. The RTLR40 is inserted into the FASTRACK guide rails and is suitable for most engineering materials, including metals, ceramics and composites.

Ease of setup

With generous setup tolerances and an integral setup LED offering real-time signal feedback, the RGH45 readhead can be installed quickly and easily.

Dual limit sensing

The RGH45 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 RGH45 outputs RS422 digital resolutions from 5 µm to 0.1 µm direct from the readhead without the need for an additional interface.

Interface option

REE interface

  • Can be used with RGH45A 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 improved cyclic error over the all-in-one digital readheads.
  • Please refer to the REE datasheet for further information.

Technical specifications

Measuring standard

FASTRACK RTLR40: stainless steel tape scale with carrier system

RTLR40-S: stainless steel tape scale with self-adhesive backing tape, for mounting directly to a substrate without FASTRACK guide rails

Readhead size (LxHxW)

44 mm x 27 mm x 17 mm

Scale pitch

40 μm

Coefficient of thermal expansion at 20 °C

10.1 ±0.2 μm/m/°C

Accuracy grade at 20 °C

Up to ±15 µm/m

Reference mark

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

Limit switches

Magnetic dual limits

Scale length

FASTRACK: 100 mm to 25 000 mm
RTLR40: up to 10 000 mm

RTLR40-S: up to 10 000 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 0.1 µm

Electrical connection

0.5 m, 1 m, 1.5 m, 3 m, 5 m cable lengths with D-type connector (15 pin)

Power supply

5 V ±5% < 160 mA (analogue, 0.4 µm, 0.2 µm, 0.1 µm ),< 125 mA (10 µm, 5 µm, 2 µm, 1 µm) (unterminated)

Vibration (system)

100 m/s2 max @ 55 to 2000 Hz

Shock (system)

500 m/s2, 11 ms, ½ sine

Operating temperature

0 °C to +55 °C



Refer to data sheets for full details.


Data sheets

Installation guides

Technical drawings

How it works

Within the readhead, an infra-red LED emits light laterally onto a scale with reflective and non-relective 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 RGH45 can be connected to the REE interface, which include Auto Gain Control (AGC) and Auto Offset Control (AOC) that operates at all speeds.

The RGH45 readhead features a set-up LED, which lights green when optimum installation has been achieved.

Reference mark and dual limits are available with this readhead. The reference mark provides a repeatable home or zero position, whilst the limits are used as end of travel indicators.

RGH45 optical scheme with annotations