Study On Distributed Temperature Sensing Technology Based On Incoherent Optical Frequency Domain Reflectometry

Distributed temperature sensor has a broad application in industry for its electromagnetic immunity, fully distributed measurement, high spatial resolution and temperature accuracy. Compared with the conventional optical time domain reflectometry, incoherent optical frequency domain reflectometry has advantages in spatial resolution, acquisition of signal, requirements of devices, and so on. Operation principle, methods of demodulation, noise characteristics and temperature accuracy of the distributed temperature sensing system based on Raman scattering and incoherent optical frequency domain reflectometry are theoretically analysed and disscussed.Computer simulations of the system with and without noise are implemented in three conditions, they are uniform distribution, distribution with a hot-spot and linear distribution. The results show that, the intensity of the Raman Stokes scattering is about four times of the Raman anti-Stokes scattering, and they are both of the order from picowatt to nanowatt. The amplitude response decays with periodical oscillation, at high frequencies, it decreased nearly four orders compared with low frequencies. The phase response is slso periodical and the temperature sensitivity of phase is higher than amplitude. When noise is considered, the signal orignated from the sensor fiber is affected obviously, especially at the frequencies over10MHz. Window filtering and wavelet denoising is adopted to reduce the noise in the temperature measurements respectively. The simulated result show that both of them are efficient to eliminat noise, and the wavelet denoising is prior to the window filtering on ordinary circunstances while the window filtering is more suitable when a hot-spot exists.Finally, the performances are evaluated when different wavelengths are chosed, dispersion is considered, the temperature distribution changes rapidly, fault point along the fiber and fiber aging is existed. And then the corresponding solutions are disscussed seperately.