A nanometer range displacement measurement system is presented where a reciprocal interferometer is employed whose configuration is similar to Michelson interferometer. Although the reciprocal interferometer is very simple and insensitive to environmental perturbations, we concluded that the spectrum analysis techniques could also be used to process the interference fringes and increase the measurement precision of reciprocal interferometry. Fast-Fourier transform and filter are used to eliminate the noises in fringes. The reconstructed fringes are very clear, which location can be measured accurately. Theoretical analysis is presented. Experimentally, the displacement of a nanopositioner-driven target was measured by using a reciprocal interferometer, a CCD camera, picture card and computer. The system has demonstrated a minimum resolution is 1.5 nm when the number of sample point is 512.
At present, many floater-type measurement equipments whose readings are recorded by manpower are still in use in petrol-chemical industries. With regard to their low efficiency, great errors and their improbability in realization in automation management and remote control, in this instance, a new liquid-level meter system using the advanced fiber-optic sensing technology based on the floater-type level meter is developed. In principle, it measures the liquid level of the oil tank by using the principle of force balance, captures and transmits the light signals by means of the fiber-optic sensing technology, adjusts the light signals from continuous impulse signals to the discontinuous by the light-code disc, then converts light impulses into voltage impulses by photoelectric elements. In configuration, it adopts a twin light source and a twin optical-channel, utilizes twin fiber detectors to record the size of the liquid level and judge the direction of the liquid level respectively. Moreover, the measuring system has been tested practically in a chemical plant, the results indicate that the measuring errors are Less than or equal to ±6mm, relative errors are <2% when its measuring range is within 0 and 1000mm.It is proved that the various indexes of the system satisfies the demand of the industries and the capability is credible.
With the rapid development of the electric power projects and electrization of industrial corporations, more and more transformers have been used. When in operation, the real time supervision of Transformer Fault is very important to the secure operation of transformer. The Infrared imaging techniques played an important role in Fault diagnosing for transformer. The infrared imaging technique based on infrared radiation knowledge, by using this technique, the Fault modes of Power transform as well as the application of infrared imaging on Power transformer were studied. Then a series of practical engineering problems, such as the image shaping principle of infrared laser device, the utilizing of infrared laser device in power transformer fault diagnosis, the working procedure in real field operation, the acquiring of heat spectrum from fault transformer in field test, the analyzing of heat image spectrum etc, were considered and overcame. Finally, an example was presented by using the studied infrared heat imaging technique to diagnose the primary transformer at Baitaling substation. The results are closely according with the real situation.
KEYWORDS: Interference (communication), Wavelets, Signal processing, Temperature metrology, Optical fibers, Temperature sensors, Light scattering, Scattering, Signal detection, Modulation
Distributed optical fiber temperature sensor system can sense the temperature changes along the optical fiber by the continuous form of distance. For the characteristics of insulation and resistance to electromagnetic interference, it has a wide using prospect in the field of petroleum and gas pipeline, tunnel and mine. The distributed temperature measurement is realized by using single channel anti-Stokes light, and the temperature and space resolution of the system can be assured. But the anti-Stokes signal will be submerged by noise because of the weakness of anti-Stokes light signal, the loss of scattering light and the system noise. In order to reduce the influence of various noises in distributed temperature measurement, the method of increasing the times of signal accumulating is used to increase temperature resolution. But this will lengthen the period of temperature measurement and influence the practical application of the system. By using the multi-resolution analysis of Wavelet to handle the distributed temperature signal, we can shorten the period of temperature measurement and enhance the response speed of system on the basis of the assurance of time and space resolutions.
A phase-locked optical-fiber fluorescence temperature sensor based on double-reference light sources is proposed, which results in a significant improvement in the measurement resolution. The system uses the methods of phase-locked, frequency modulation and phase modulation. The double-reference light sources is used to solve the leakage of intrinsic exciting light which has influence on fluorescence decay signal. Ruby of fluorescent substance is used as sensor material in the system. The probe is tested in the temperature range from 0°C to 200°C. The experimental result shows that the system of measurement temperature is feasible and also proposed to be used for the highly accurate monitoring of the real time.
This paper described the distributed optical fiber temperature sensing system based on Brillouin amplifier structure, which combined Brillouin amplifier effect with optical time domain reflection(OTDR). With the relationship of temperature and stimulated Brillouin frequency shift, we can obtain the temperature on each point. Based on this principle, some experiments were taken, then the linear relationship and experimental data were given, which provided powerful foundation for future research.
Distributed optical fiber temperature sensor use the principle of temperature effect of spontaneous Raman scattering in fiber and optical domain time reflection (OTDR) to detect the temperature field in space and its changing with time. It can sense the temperature changes along the fiber length by the continuous form of distance in a fiber of several kilometers length. Theoretically, the minimal discernible space length of fiber in the distributed optical fiber temperature sensor system is proportional to the width of incident light pulse, that is, the narrower the width of incident light pulse, the higher the space resolution of fiber. The width, power and edge quality of incident light pulse can directly influence the space and temperature resolution of distributed optical fiber temperature sensing system. This paper focused on the optimum design of light pulse producing based on the use of LD light source. A high power light pulse of narrower width is produced by designing reasonable circuit of increasing voltage, discharging control and making full use of LD, which makes sure to improve the space and temperature resolution of the system.
This paper describes an efficient method for in-situ measurement of chlorophyll-a concentration in the seawater with fluorescence method and optical fiber techniques. The instrument uses the pulsed xenon lamp as the excited light resources. Both the exciting light and the fluorescence from algae chlorophyll-a are transmitted along two fiber bundles. The fluorescent signal is detected by using the relevant pulsed detecting technology. The minimal detecting concentration of chlorophyll-a in the ocean can reach 1x10-5mg/cm3. The system has advantages of simple structure, passive sensor head and high sensitivity. The experimental results show that this measurement method is realizable.
The distributed optical fiber temperature sensing system based on the Raman back scattering has been widely used. By using the optical time domain reflection (OTDR) technique, the high intensity light pulse is coupled into optical fiber. By detecting and recording the variation of back scattering signal related to optical fiber temperature along with the time, the distribution measurement of environmental temperature is carried out. In order to ensure a certain intensity of the light pulse, it must have a certain width. In the meanwhile, the responding rate of the photoelectric components and the bandwidth of the digital collection systems cause the reduction of the space resolution. The signal coupling brought by the pulse width can be reduced and the space resolution of distributed optical fiber temperature sensing system can be improved by using self-adaptive wavelet nerve network which has a stronger ability of function approach and tolerant fault to process the data.
This paper presents a monitoring temperature system in real time. The fluoroptic temperature could be detected quantitatively by the signals of PSD. When the optical fiber is 2 m long, the real-time temperature sensitivity is 0.1 degrees Celsius and the accuracy is 1%. The high sensitivity and high accuracy are partly due to the operation of the light source feedback, and partly due to the ratio of measurement and reference signals. This fluorescence temperature measuring system finds wide application fields where conventional techniques either cannot be used, or have proven to be unsatisfactory. It is especially useful for measurements in electrically hostile environments.
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