Home > Fibre-optic broadband cables fed underground with the help of Renishaw’s RM22 magnetic encoders

Fibre-optic broadband cables fed underground with the help of Renishaw’s RM22 magnetic encoders

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article image Renishaw non-contact RM22 magnetic encoders help detect slippage
Two Renishaw non-contact RM22 magnetic encoders were incorporated into a specially fabricated machine designed to thread fibre-optic cables into underground ducts without causing damage.

Countries moving to high-speed, fibre-optic broadband face a significant challenge to replace the mass of existing underground cables with new fibre optic cables. The fragile individual glass fibre strands and the sheathed fibre-bundles run the risk of damage when being pulled into the ducts.

One telecommunications company discovered that air blown at high pressure when threading a fibre-bundle into a sealed duct provided a lubricating effect and also helped to propel the cable along. The result is that far less force is required to thread the bundle, considerably reducing the risk of damage to the fibres and potentially making the broadband upgrading process quicker, easier and safer.

UK-based Factair Ltd, an expert in air compressor systems won the contract to manufacture the patented, field-based ‘fibre-blowing' machine, which uses caterpillar tracks to thread the fibre-optic bundle quickly into the duct, whilst introducing compressed air in order to propel the bundle along.

Harsh environment calls for magnetic encoders

Two Renishaw non-contact RM22 magnetic encoders have been incorporated into the machine to detect slippage that would damage the surface of the sheath. While one Renishaw encoder monitors the rate at which the bundle is threaded into the machine, the other monitors the rate at which the caterpillar belts are moving.

The fibre-blowing machine's control unit counts the pulses from both encoders and if the difference in count rate is outside the tolerance setting, it interprets the difference as slip and reduces the speed of the motors. As an additional safeguard, the motor is also ‘capped' to limit the push force if the cable's progress in the duct is hindered, preventing motor burnout.

Nitzan Gonen, Factair's Design and Development Director explains that non-contact encoders are required for the application because the fibre-bundles are un-spooled on-site from large drums, which can be wet and dirty if the weather and local conditions are poor. A non-contact unit offers increased reliability and durability unlike a full-contact encoder that would probably need to be replaced often.

Extremely satisfied with the Renishaw encoders, he confirms that the units are built to work reliably at far higher speeds, and in far worse conditions than being encountered now.

The fibre-blowing machine has enabled the engineers to feed the cable without damaging the sheath or fibres from a few tens of metres, to thousands of metres.

Renishaw’s RM22 non-contact magnetic encoders use Hall-effect sensor technology where the rotation of the magnetic actuator is sensed by a custom encoder chip within a separate body, and processed to give the required output format.

Key features of Renishaw RM22 non-contact magnetic encoders:

  • Rugged build with tough aluminium alloy body withstands harsh environments
  • Enclosed in stainless steel to provide dirt immunity to IP68
  • Immunity to liquids, oils and dirty environments eliminates requirement for seals
  • Non-contact body measures just 22mm in diameter with speed capability to 30,000 rpm
  • Frictionless design increases durability, endurance and long-term reliability
Renishaw Oceania represents the Renishaw Group in Australia and New Zealand.

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