Community Research and Development Information Service - CORDIS

FP5

ZEM Report Summary

Project ID: G1RD-CT-2001-00543
Funded under: FP5-GROWTH
Country: Switzerland

SOFO static and dynamic measurement system (remote sensing system)

The SOFO Reading Unit is computerized equipment that measures all SOFO sensors. It includes an optical source, a mobile mirror, a photo-detector and the related electronics. These components are contained within a case designed to withstand the harsh environment of a civil engineering construction site. The unit is powered either by the internal battery or by an AC source. An external portable PC controls the Reading Unit allowing to initiate the measurements and store the obtained results for further analysis. A single Reading Unit allows the measurements of an unlimited number of sensors.

Optical switching units are used to automatically multiplex different sensors. SOFO V units are available in single channel configuration used for manual measurements, with an integrated switching having unit up to 12 channels, or with external units having up to 100 channels each. Internal and external units can be cascaded to reach even a greater number of channels. A standard serial link connects the SOFO unit with the control PC, while the SOFObus port is used to connect external switching units and external data acquisition devices to the SOFO Reading Unit.

The SOFO V Reading Unit contains a data logged that can be programmed to automatically read SOFO sensors and external data acquisition devices and store the measurements in its memory. The memory can hold thousands of measurements that can be later downloaded into the SOFO SDB database. A modem (standard, radio, cellular, cable, fibre optic or Ethernet) can be connected to the SOFO unit to allow remote measurement, check the unit's status, or download data from the SOFOV memory.

The SOFO Dynamic reading unit allows measuring SOFO sensors at high frequencies. One reading unit can be used to demodulate up to 8 channels. Multiple units can be combined when higher channel counts are needed. The SOFO Dynamic reading unit can be used in conjunction with SOFO sensors. SOFO Dynamic compatible sensors can be measured with both the SOFO Dynamic (dynamic measurements) and the SOFO V reading unit (static and long-term measurements, reduced range). Most standard SOFO sensors can be measured by the SOFO Dynamic reading unit using an external custom -made compensator.

The SOFO Dynamic reading unit is based on a heterodyne low-coherence interferometer operating at 1550nm. The optical signal is phase modulated by the demodulation interferometer. After detection, the reading unit tracks the phase modulation introduced by the sensors and converts it into a displacement. The resulting deformation is available in analogue form on the analogue outputs or in digital form on the USB connection that can be used to transfer the measurements directly to a PC for storage and further analysis. The measurements are relative and the zero point is lost on power off, but can be recalibrated using the SOFO V reading unit.

Application domains: Measurements of dynamic deformations of structures under, dynamic loads such as traffic, wind, seismic, waves, Evaluation of dynamic amplification factors, System identification through modal analysis (ambient and forced vibrations). Determination of mode-shapes and modal curvatures. Damage detection through changes in modal parameters, stiffness and damping factors, Weight-in-motion through structural response

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