Fiber Bragg gratings (FBGs) sensor has been widely used in all kinds of detection spaces. Nonlinear effects of the fiber Bragg gratings have been observed in high-temperature conditions, however, it occurred in low-temperature as well. In this paper, we take the low-temperature experiments in the low-temperature thermostat bath, temperature range from 10°C to -80°C, the Bragg wavelength shift with the temperature decreasing linearly at the very beginning and it shows linear characteristic range from room temperature to -45°C. However with the temperature goes down continuously, the nonlinear effects emerged, the turning point temperature of the nonlinear effect is at -45.3°C. Besides, the sensitivity of the FBGs decreased as well from 8.96pm/°C to 6.72pm/°C. Considering the physical characteristic of the silica fiber, which the thermo-optic coefficient and the thermal expansion coefficient of the fused silica is not constant if temperature goes down and it shows nonlinear features, therefore we conclude the nonlinear effect at low-temperature is attributed to the thermal expansion and the thermo-optic effect of the silica fiber. Thus, we predict that appropriate doping improvements in the silica fiber can modify the linear range of FBGs which can enhance the measure precision. In addition, we find that high sensitivity FBGs has a lower temperature turning point of the nonlinear effect. The invar packaged FBGs has a sensitivity of 24.3pm/°C at room temperature. It is higher than bare FBGs’ sensitivity which is about 8.96pm/°C at room temperature. The invar packaged FBGs’ temperature turning point is at about -54.5°C, which is lower than the bare FBGs’, -45.3°C, temperature turning point. This indicates that high sensitivity FBGs can also increase the linear temperature range. The experiment results and analysis show that we can either by increasing the sensitivity of FBGs or doping in the silica fiber to modify the linear range.
In recent years, Fiber Bragg Grating (FBG) sensors have been attracted a lot of interest, and widely and
increasingly researched in many important areas. In this work, we present the field of railway dynamic monitor
concerning the application of FBG sensors. We have built the principle and established the sensing system based on FBG
to monitor the situation of train and railway through the analysis of track strain during the train passage. We have
illustrated that FBG sensors set on the lateral and underside of the rail can detect the strain of rail and sensors on
different positions show distinct results. We have presented that the underside of the rail structure is the most suitable
position to monitor the strain in railway.
In the past few years, fiber Bragg grating (FBG) sensors have attracted a lot of interest and there were number of studies
on the use of FBG sensors to detect the strain of steelworks. This paper describes the strain sensors based on FBG with
different package used for steelwork. Strain distribution of the steelwork is predicted through Finite element analysis.
Bare FBG, FBG sensor packaged with steel sheet and resistance strain gauges are set on the same specified location of
steel specimen, and load is added on the steelwork by rally machine. Strain values of the steel specimen can be caught by
three kinds of sensors when load is stabilized. Then the load added on the steelwork is changed from 0KN to 50KN and
back to 0KN, meanwhile the values of strain are recorded respectively. Results of three sensors are compared mutually
and are all close to theoretical values provided by FEA.
KEYWORDS: Fiber Bragg gratings, Sensors, Resistance, Temperature metrology, Structural health monitoring, Optical sensing, Sensor technology, Signal processing, Temperature sensors, Fluctuations and noise
Over the last few years, fiber Bragg grating (FBG) sensors have attracted a lot of interest and they are being used in
various applications. This paper describes the FBG sensors used for strain monitoring of bogie and other steelworks.
FBG sensors and resistance strain gauges are set on different position of steel girder, and weight is loaded on the steel
girder. Strain value of the steel girder can be caught by two kinds of sensors when weight loaded is changed. Result of
experiment shows that strain value obtained by resistance strain gauges and FBG sensor is coinciding. There is a linear
correlation between value of strain and the weight loaded on the steel girder. FBG sensors with different encapsulations
are set on bogie by acrylic plastic materials in order to monitor its dynamic strains. When sinusoidal load with its
frequency from 0.15Hz to 2Hz was set on the bogie, FBG sensor system with data sampling rate of 20Hz were used to
monitoring the dynamic strains. Strain data caught by FBG sensor system can offer accurate description of dynamic
strain, and value of strain provided by FBG sensor suits theoretical values well. The experimental observations show that
FBG sensors can be set on steelworks easily, and can monitor both static strain and dynamic strains well.
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