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Instrumentation Service

Deformation Monitoring with Fiber Optic Sensors (SOFO V)

Keywords: SOFO, fiber optic sensor, health monitoring, displacement, strain, Michelson interferometer

Setup of SOFO VSetup of SOFO V

SOFO (a French acronym for Surveillance d'Ouvrages par Fibres Optiques) is a deformation measurement system based on low-coherence interferometry using an fiber optic sensor.

The sensor consists of a pair of single-mode fibers installed in the structure to be monitored. One of the fibers, called the measurement fiber, is housed in a pipe, attached at the two ends of the measurement zone and pre-tensioned in between. The other fiber, called the reference fiber, is placed loose in the same pipe. All deformation of the structure changes the difference in length between the two fibers.
To make an absolute measurement of this path imbalance, a low-coherence double Michelson interferometer is used. The first channel consists of the measurement and reference fibers, while the second is contained in the portable reading unit.

Features

  • Excellent long-term stability
  • Long-gage fiber optic deformation sensor
  • High resolution: 0.002 mm
  • Easy and quick to install and measure
  • Embeddable in concrete
  • Automatic and remote operation
  • Insensitive to temperature, EM fields, corrosion

System specifications

Reading unit (SOFO V)

  • Resolution: 0.002 mm (independent of gage length)
  • Precision: Better than 0.2% of the measured deformation
  • Size: 470 x 390 x 175 mm (Weight: 13 kg)
  • Operating temperature: -20°C~60°C
  • Max. number of channels: Unlimited
  • Data logger capacity: Max. 80,000 measurements
  • Automatic measurement: Interval can be set with a PC
  • Remote measurement: By PHS, cellular phone, fixed line

SOFO sensor

  • Gage length: 0.2~50 m (Diameter: 8 mm)
  • Dynamic range: Elongation: 1.0%
                             Contraction: 0.5%
  • Operating temperature: -50°C~110°C
  • Watertight: 6 bar
  • Calibration: Not necessary
  • Temperature sensitivity: 0.5 μm/°C
  • Insensitive to temperature, EM fields, corrosion

Applications

SOFO Photo1 SOFO Photo2 SOFO Photo3
Deformation measurement
of a concrete bridge deck		 Deformation measurement of a containment vessel Embedded in concrete

Experience: SOFO systems have been used in over 120 projects all over the world (as of 2004).