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Fast and accurate deformation measuring techniques show promising potential for monitoring high-temperature piping and other machinery in the energy sector, such as in thermal, steam, or nuclear power plants. Optics-based, nonintrusive, and real-time monitoring systems are critical for preventing high-temperature steam leaks, unexpected accidents, explosions, and other failures that can have catastrophic consequences for the power supply, the workers, and the public. In this study, a dynamic thermal deformation measurement technique utilizing the sampling Moiré method and grating magnets is developed for large-scale, high-temperature piping in a thermal power plant. Because of the high temperature of the piping of nearly 300 °C several 100 mm by 100 mm ferrite magnets were placed to select locations of the high-temperature piping. In each ferrite magnet, a regular, two-dimensional binary grating pattern with a pitch of 15 mm was painted on the surface, and the grating magnets were used as the reference grating to analyze the small in-plane displacement distribution using the sampling Moiré method. A compensation method of misalignment angle is also proposed to improve the measurement accuracy. The effect on vibration remove, mirage due to conversion in air, wide angle of camera lens, and compensation of misalignment angle, are discussed. The experimental results showed that our measurement technique is suitable for evaluation of high-temperature, large-scale infrastructure. [ABSTRACT FROM AUTHOR]

Measuring accurate displacement distributions for large-scale structures is an important issue and a very challenging task. Recently, a simple and accurate phase measurement technique called sampling moiré method [Exp Mech 50-4:501-508, ()] has been developed for small-displacement distribution measurements. In this method, the phase distribution of moiré fringes can be analyzed from a single grating image by simultaneously performing down-sampling image processing and intensity-interpolation to generate multiple phase-shifted moiré fringe images. In addition, the phase of the original grating can also be obtained from the phase of the moiré fringe by adding the phase of the sampling grating. In this study, the measurement accuracy of the sampling moiré method was analyzed through computer simulations and a displacement measurement experiment. Four factors of the sampling moiré method were investigated, including the sampling pitch, the order of the intensity-interpolation, random noise, and the form of grating. The results show that determining the optimal sampling pitch is an important factor for obtaining better results but it is not critical. In addition, a practical application of the sampling moiré method is presented that involves a deflection measurement on a 10-meter-long crane. The experimental results demonstrate that submillimeter deflections of the crane can be successfully detected. [ABSTRACT FROM AUTHOR]

In this paper, a novel accurate deformation distribution measurement technique by using sampling moiré method is proposed. The basic principle and an experimental result of a steel beam in symmetric three-point bending are reported. In this method, the measurement area of a target is attached with an adhesive tape of a known pitch grating firstly. An ordinary CCD camera is installed on a fixed point to record the image during deformation. The captured image is analyzed by performing easy image processing, i.e., thinning-out and linear interpolation, to obtain the multiple phase-shifted moiré patterns. Then, the phase distribution of the moiré pattern can be calculated using phase-shifting method. Finally, the deformation distribution is calculated by the grating pitch times the phase difference of before deformation and after deformation. The experimental results in symmetric three-point bending test show that the displacement of the steel beam at loading point agree well with those obtained by an accurate displacement sensor. The average error of displacement measurement is less than 4 μm when 2 mm grating pitch is used, and it corresponds to 1/500 of the grating pitch accuracy. This indicates that noncontact deformation distribution measurement is possible by simple and easy procedure with high accuracy, high speed, and low cost for the structural evaluation of infrastructures. [ABSTRACT FROM AUTHOR]