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Displacement tunnel sensor (displacement gauge)

Real-time monitoring of displacement changes in tunnel walls

The Displacement tunnel sensor is a fiber optic strain sensor based on Fiber Bragg Grating (FBG) technology. It is specially constructed for real time measurement of displacement of disturbed  surfaces of the tunnel’s concrete layers. The aim is to detect flaking of concrete layers of the tunnel surface, which then allows for continuous structural health monitoring.

  • 100% passive sensor without the need for power 
  • excellent fatigue resistance
  • suitable for remote sensing

100% passive sensor

The tunnel sensor does not require any power, and hence can be used for monitoring areas without access to any power, as well as hazardous or inaccessible areas.

Fatigue resistance

The Displacement tunnel sensor features excellent fatigue resistance and can therefore be used to monitor the accumulation of any structural damage in important structural and mechanical components which bear immense cyclic loads before failing.

Remote sensing

The Displacement tunnel sensor is highly suitable for remote sensing, as it can be installed several kilometers away from the measurement unit.

Protected as IP68 rated devices

The IP68 rating guarantees complete dust tightness and protection against the effects of long immersions in water.

Immune to EMI/RFI

The tunnel sensor enables operation in harsh environments and hazardous areas. The advantage is its immunity to electromagnetic/radio frequency interference.

High sensitivity and accuracy

The fiber optic tunnel monitoring sensor is designed for measurements with the  accuracy of micrometers.

Universal platform

Together with the tunnel sensor you can also use other sensor types (temperature, inclination, vibration, strain, etc.).

Low installation costs

Installation and cabling for such sensor networks are much less expensive and less cumbersome than comparable electronic gauge networks.

Excellent long-term stability

The Displacement tunnel sensor is highly durable and reliable even in demanding environments. This makes it especially suitable for a long term field operation.

Smart transduction mechanism

The smart transduction mechanism converts the displacement between the concrete layer and the sandstone masonry to optical fiber elongation.


The tunnel sensor can be used alone or incorporated into large sensing networks.

Leverage the existing fiber optic network

Standard telecommunication optical fibers, for example, dark fibers, can connect the unit and sensors. This is very economical even for a large number of monitored points.

Composed of a metal tube and mounting head

The Displacement tunnel sensor is composed of a metal tube and a special mounting head. The metal tube is fixed in the hole of the tunnel wall and the head is mounted to the surface of the tunnel.

Advanced customization available

The tunnel monitoring sensor can be customized for your project, for example replacing metal parts with plastics for high-voltage environments.

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