Health Monitoring Of Large Structures Research Articles

Temperature Compensation of a Strain Sensing Signal from a Fiber Optic Brillouin Optical Time Domain Analysis Sensor

In order to do continuous health monitoring of large structures, it is necessary that the distributed sensing of strain and temperature of the structures be measured. So, we present the temperature compensation of a signal from a fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor. A fiber optic BOTDA sensor has good performance of strain measurement. However, the signal of a fiber optic BOTDA sensor is influenced by strain and temperature. Therefore, we applied an optical fiber on the beam as follows: one part of the fiber, which is sensitive to the strain and the temperature, is bonded on the surface of the beam and another part of the fiber, which is only sensitive to the temperature, is located nearby the strain sensing fiber. Therefore, the strains can be determined from the strain sensing fiber while compensating for the temperature from the temperature sensing fiber. These measured strains were compared with the strains from electrical strain gages. After temperature compensation, it was concluded that the strains from the fiber optic BOTDA sensor had good coincidence with those values of the conventional electrical strain gages.

Fibre optic sensor network for spacecraft health monitoring

Close meshed instrumentation or sensor networks applyingconventional sensors for temperature and strain monitoring may result inexcessive penalties in terms of weight constraints, reliability andsensitivity to environmental conditions, and complex interfaces. Thefibre-optic sensor network described in this paper is a multiplexed system offibre Bragg grating (FBG) strain and temperature sensors and was designed anddeveloped for a demanding space environment, but it can also be emphasized asa promising sensor technology with high potential for non-space applications.The FBG sensor network measures both strain and temperature at the measuringconditions of the structural core of the X-38 spacecraft, by means ofwavelength shifts due to tensile stress on a Bragg grating. Dependent on thefixation of the fibre, either isolated from or mechanically coupled to thestructure, local thermal or mechanical loads can be determined in thetemperature range from -40 to +190 °C, and in the strainrange from -0.1% to +0.3%. Short-term resolution and repeatabilityof the strain measurement amount to 5 µε and25 µε, respectively.The FBG sensor network is very suitable for structural health monitoring oflarge structures, i.e. to determine thermal and mechanical load profilesduring operation, to assess residual strength of structural elements orto detect irregular working conditions. In comparison to conventional sensorslike thermocouples and strain gauges, an FBG sensor network significantlyreduces the amount of required front end electronics (FEE) and harness.