LOCK: low-cost crack monitoring system - Romolo Di Francesco

LOCK: low-cost crack
monitoring system
The miniaturized two channel crack monitoring system with wireless capability
LOCK IS THE FIRST LOW-COST FIBER-BASED CRACK MONITORING
SYSTEM.
Fiber optic sensors are attracting an
increasing interest in structural health
monitoring (civil engineering, cultural heritage
preservation, etc.) due to their unique
properties, and particularly for their immunity
to electromagnetic interferences and
impossibility to start fires. Their widespread
usage, however, is still hampered by the high
cost of commercial systems.
The research activity at the Department of
Electronics of Politecnico di Torino (Torino,
Italy), one of the most prestigious European
technical universities, has led to the
development of LOCK, an optical fiberbased
crack monitoring system
specifically conceived for permanent
monitoring of cracks and characterized by
a very favorable price/performance ratio,
comparable to that of the more common
electro-mechanical strain-gauges.
Therefore, the LOCK system allows bringing
all the advantages of a fiber-based
monitoring system also to monuments and
building relevant for local communities only
or when budget constraints are particularly
tight.

Detail of the sensor
characterization setup
THE LOCK SYSTEM
The LOCK system uses a modular approach
to satisfy all the crack monitoring needs:
from a local unit able to control 2-16 cracks,
to complex configurations for large
monuments where several two-channel
devices are connected to a main control unit
using wireless links.
Plastic optical fiber (POF) based transducers
with different embodiments working in
transmission and reflection configurations
have been developed to , depending on the
required performance. Feeding fibers can be
transparent to minimize visual impact and
have diameters from 1/4 mm to 1 mm.
The choice of using plastic fibers allows
lowering the system cost and a remarkable
simplification in the installation since
complex and expensive tools are not
necessary.
MAIN CHARACTERISTICS OF THE LOCK SYSTEM
Interrogation capabilities: modular and customizable since the basic two-channel module can be used as stand-alone reading unit
or arranged into multi-channel interrogators
Sensor types: different embodiment are available using either transmission or reflection configurations depending on the
measurement requirements and the wall where they are supposed to be fixed
Performances: short/medium term accuracy better than 1/100 mm, long term accuracy better than 1/10 mm
Power supply: control unit from mains; wireless two-channel modules are battery operated with a lifetime exceeding one year (exact
value depends on the number of measurements required)
PC interface: USB port; possible customization with wireless (Wi-Fi, Zig-Bee or GSM) modules
Software: sensor response analysis with data filtering
The eight channel control unit (with
remote connection capability using
the mobile phone GSM network)
installed in a prestigious monument in
Venice.
Example of application of a
sensor in “transmission”
configuration with jacketed 1 mm
feeding fibers.
Example of application of a sensor in
“reflection” configuration with bare
(transparent) 0.5 mm feeding fibers.
This brochure describes a demonstrator built in the framework of a research project carried out by the groups of
“Fiber and Optical Components” and of “Automatic Measurement Systems” of the Department of Electronics of
Politecnico di Torino. The specifications here reported are just preliminary results and subject to change without
notice to reflect the development of the equipment. For further information, please contact:
Guido Perrone
Politecnico di Torino - Dept. of Electronics
T/+39 011 0904146 F/+39 011 0904099
C.so Duca degli Abruzzi 24 Torino, TO I-10129
www.fco.delen.polito.it
© G. Perrone - Politecnico di Torino - 2009