A novel target type flow sensor has been proposed for liquid flow measurement in pipeline. The force created by the fluid on the target results in the distortion of a cantilever structure. A couple of fiber Bragg gratings (FBGs) are mounted at either side of the cantilever. By monitoring the wavelength shift difference of the two FBGs, the fluid flow-rate can be obtained and the cross-sensitive problem of the FBG sensor can be solved by compensating the temperature effect. Measurement theory has been described. Simulation and preliminary experiments have been carried out, and the results verify the feasibility of the proposed sensor with a measurement range from 0 to 1000 cm3/s.

Experimental setup for current measurement and a novel signal detection method for demodulation of fiber Bragg grating wavelength shift are developed. Being attached respectively on the upper and lower surface of a pendulum-type cantilever element, only a couple of matched FBGs are used for both current sensing and wavelength shift signal demodulating. So, the received light power will change due to the split of the two reflected spectrum of FBGs, which is corresponding to the electromagnetic force caused by the measured current. In addition, cross-sensitivity effect of FBG-based sensor automatically solved due to a differential signal process method. Static and quasistatic measurement results indicate the feasibility of the developed sensor system. Measurement error of

Fiber Bragg grating (FBG) sensors are one of the most exciting developments in the fields of fiber-optic sensors in recent years. One of the problems in using grating sensors is the discrimination of temperature and strain responses (cross-sensitivity effect between temperature and strain), because in most real-world applications both of these quantities will be acting on the sensor elements. Another problem is how to measure a small Bragg wavelength shift accurately. This article presents a comprehensive and systematic overview of discrimination measurement methods and demodulation techniques for FBG sensors. It is anticipated that FBG sensors will be commercialized and widely applied in practice in the near future due to the maturity of economical production of FBGs and the availability of cost effective measurement and demodulation techniques. Recent research work about a differential FBG sensor for simultaneous measurement of down-hole high pressure and temperature and the corresponding demodulation techniques are also introduced in this paper.

The refractive index of salt water changes corresponding to the variation of salinity. Based on a differential refractometer, the salinity canbe measured due to beam deviation, and the influence of temperature on the measurement results is reduced effectively. Beam deviation caused by salinity change is detected by a fiber-optic array and recorded by a charge-coupled device. According to the Gauss distribution theory, the light-spot center can be determined by fitting a Gauss curve using each received light spot intensity and the position of each receiving fiber. With this method, measurement errors caused by light power fluctuation and ambient light disturbance can be avoided effectively. Variation in transmission power loss of each receiving fiber reduces the measurement accuracy of salinity. Therefore, a method of correction for each fiber transmission power loss in the array can effectively improve the salinity measurement accuracy. Experimental results indicate the feasibility of the developed system, and the measurement repeatability error is better than ±0.25‰.

Based on near-infrared spectral absorption and fiber-optic sensor technology, an experimental setup for low-water-content measurement of crude oil is developed. The advantages of this method include fast measurement, high accuracy, keeping the measured oil free of pollution, and being suitable for long-term on-line continuous monitoring. This technology can be used for those applications that require high-quality water-in-oil measurement and process control. The measurement resolution for water content is better than 0.005% in the range from zero to 2% by volume. Measurement errors are estimated to be