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RGH25F UHV incremental encoder system with RGS20 linear scale


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


  • Ultra-high vacuum (UHV) compatible readhead
  • Ultra compact readhead
  • Auto Gain Control (AGC) for excellent signal integrity
  • Scale lengths available up to 50 m (>50 m special order only)
  • ‘Cut-to-length' scale flexibility
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What is RGH25F UHV?

The RGH25F ultra-high vacuum (UHV) readhead has been manufactured using materials and adhesives specially selected for their low out-gassing rates. The product is then packed and sealed in a vacuum-compliant bag to ensure cleanliness is maintained. The RGH25F UHV readhead is used with the REF interface which incorporates automatic gain control and unique self-tuning adaptive electronics to maintain signal integrity.

What is RGS20 scale?

RGS20 is a tape scale manufactured from a thin flexible steel strip, featuring a 20 µm pitch, which is gold plated to give high reflectivity and corrosion resistance. It may be mounted using UHV compatible adhesive backing tape, to most engineering materials, including metals, ceramics and composites. Secured to the substrate with scale end-clamps, RGS20 is mastered to the substrate and will match the substrate's thermal expansion. The scale is supplied on a reel and can be cut to suit any axis length up to 50 m.

Why choose this encoder system?


The RGH25F UHV vacuum readhead has been specially constructed from clean UHV compatible materials and adhesives to give low outgassing rates and a clean RGA. These readheads also feature reduced current consumption to minimise heat dissipation.


The low profile RGH25F UHV 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.

Long lengths

The RGS20 tape scale is available in lengths up to 50 m (contact Renishaw to discuss longer lengths).

Technical specifications

Measuring standard

Gold plated steel tape with protective lacquer or polyester coating

Readhead size (LxWxH)

36 mm x 13.5 mm x 10.5 mm

Scale pitch

20 μm

Coefficient of thermal expansion

Matched to substrate material when scale ends are fixed with end clamps

Accuracy grade

±15 μm/m (±3 μm/m when 2-point compensation is applied)

Reference mark

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

Limit switch

Optional single limit (select at time of order)

Scale length

Up to 50 000 mm

Maximum speed



(with REF interface):

Up to 6 m/s at -3 dB

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



(with REF interface):

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-type connector (15 pin)

Power supply

5 V –5%, +10%, 200 mA maximum (unterminated)

Readhead power consumption50 mA

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

Bake-out temperature(non-operating)

120 °C (Readhead and scale only)


Readhead: IP40

Interface: IP20

Cable construction

Tinned copper braided single screen. PTFE core insulation

Refer to data sheets for full details.



Data sheets

Technical drawings

How it works

Within the readhead, an infra-red LED emits light onto the angled scale graduations where it is directed back 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.

RG2 optical scheme with annotations