Displacement tunnel sensor

Displacement tunnel sensor

The displacement tunnel sensor is a strain fiber optic sensor which is constructed for the measurement of displacement of disturbed areas in the concrete layer in tunnels. It is based on Fiber Bragg Grating (FBG) technology and the smart transduction mechanism converts the displacement between the concrete layer and the sandstone masonry to the optical fiber elongation. The sensor can provide an accuracy of micrometers and is composed of a metal tube and special mounting head. The metal tube is fixed in the hole of the tunnel wall and the head of the sensor is mounted to the surface of the tunnel.

The Displacement Tunnel Sensor FBGS-01D features high accuracy and resolution, and immunity to electric sparks and EMI/RFI. It is suitable for remote sensing and it is possible to install it kilometers away from the measurement unit. It is protected against complete, continuous submersion in water guaranteeing IP68 protection.


  • Immune to all electromagnetic effects and safe operation in harsh environments
  • High strength FBG, implying high strain levels and excellent fatigue resistance
  • High sensitivity
  • Self-referenced
  • Zero power
  • Long-term reliability
  • Large scale integration
  • Intrinsically safe design


The displacement tunnel sensor is used for real-time measurement of strain changes on the surface in the tunnel to detect flaking of concrete layers of the tunnel surface. This allows continuous structural health monitoring. Electrical power is not necessary on-site, an interrogator can be placed tens of kilometers away.


Sensor length 0,5 m
Strain range -0,5 % shortening and +1 % elongation
Strain sensitivity 1,2 pm/με
Operating temperature -20 °C up to +60 °C
Pigtail length 0,5m
Central wavelength 1510 to 1590 nm
Connector type FC/APC (standard)
Housing material SST
Cross sensitivity 10 pm/ºC

Displacement Tunnel Sensor




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