Considering the choice of sensors in optical fiber temperature sensing field, temperature
measurement experiments on fiber Bragg grating, optical fiber Brillouin scattering, Raman Scattering
Fiber Optic sensors which are based on three different theories were carried out, so temperature
measurement results are obtained, meanwhile, the temperature characteristics these three kinds of
sensors can get known by comparison between sensing principle and experimental data. This can
provide a reference for application of fiber optic temperature sensor in the temperature monitoring field.
Casing pipes in oil well constructions may suddenly buckle inward as their inside and outside hydrostatic pressure
difference increases. For the safety of construction workers and the steady development of oil industries, it is critically
important to measure the stress state of a casing pipe. This study develops a rugged, real-time monitoring, and warning
system that combines the distributed Brillouin Scattering Time Domain Reflectometry (BOTDR) and the discrete fiber
Bragg grating (FBG) measurement. The BOTDR optical fiber sensors were embedded with no optical fiber splice joints
in a fiber reinforced polymer (FRP) rebar and the FBG sensors were wrapped in epoxy resins and glass clothes, both
installed during the segmental construction of casing pipes. In-situ tests indicate that the proposed sensing system and
installation technique can survive the downhole driving process of casing pipes, withstand a harsh service environment,
and remain in tact with the casing pipes for compatible strain measurements. The relative error of the measured strains
between the distributed and discrete sensors is less than 12%. The FBG sensors successfully measured the maximum horizontal principal stress with a relative error of 6.7% in comparison with a cross multi-pole array acoustic instrument.
It is still a big challenge to set up a durable and stable long-term liquid pressure monitoring system at many points for
long pipeline under harsh environment. In this paper, according to the need from customers, a practical high-reliable
liquid pressure sensor based on dual optical fiber Bragg grating (FBGs) has been studied and developed. The FBG-based
liquid sensor structure has been brought forward and optimized, and its sensing principle has also been given in details.
Besides, the novel sensor has been tested by serious experiments. The research results show that the FBG-based liquid
pressure sensor has good linearity, repetition and immunity of temperature changes, and the theoretical sensitivity agrees
well with that from the experimental results. Such kind of FBG-based liquid pressure sensor can be applied in practical
applications.
FBG sensors are more and more accepted in most area of Structure Health Monitoring. However, due to the fact that
FBG senses both strain and temperature is monitored simultaneously, temperature compensation for FBG strain sensors
of long-term structural monitoring is indispensable. In this paper, based on the FBG's strain and temperature sensing
principles, a novel FBG-based sensor for simultaneous dual-measurement of pressure and temperature has been
developed. Firstly, in consideration of the requirement of sensors, a novel sensor structure has been designed and its
sensing principle is given in details. Secondly, the properties of FBG-based sensor for simultaneous dual-measurement
of pressure have been tested by some experiments. Finally, theoretical sensitivity has been compared with that from
experiments. The research results show that the FBG-based sensor for simultaneous dual-measurement of pressure has
good linearity, repetition, immunity of temperature changes. Such kind of FBG-based sensor for simultaneous
dual-measurement ofpressure can be used to practical monitors.
Fiber Bragg Grating sensors are widely used in the field of optical sensing system for the Structure Health Monitoring
(SHM) during the last 10 years. It can be used for monitoring the strain, temperature pressure and some other characters
of the structure. In this paper a new kind of surface sticking strain sensor with sensitivity enhanced has been studied and
developed. The structure of the sensors is presented and the Ansys software has been used to optimize the structure. A
novel theory about how to enhance the sensitivity or widen the scale of the strain sensors based on FBG is introduced
too. Based on the theory two types of sensor have been developed. One is the long-scale sensor that is able to monitor
the big strain such as crack, the other is the high-precision sensor that is able to monitor the micro strain as O.5,&mgr;&Vegr; , and
we conclude the sensitivity enhancing coefficient. As the sensitivity coefficient of bare fiber is 1 .2pm/&mgr;&Vegr; ,the theoretical
enhancing sensitivity coefficient of long-scale sensor is K=3.3811 and the theoretical enhancing sensitivity coefficient
of high-precision sensor is K=O.58. Then groups of experiments were carried out to validate the theory. The
experimental sensitivity coefficient of long-scale sensor is O.35pm/&Vegr; with the coefficient of enhancing sensitivity
is K=3.4286. The experimental sensitivity coefficient of high-precision sensor is 1.96pm/&mgr;&Vegr; with the coefficient of
enhancing sensitivity is K=0.61 . Comparing the experimental results with the theory results, it proves that the two types
of strain sensors can really reflect the strain status and the damage information of the structure, and it is stable and
reliable for the practical project.
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