Fiber-optic reflex sensor for in-line production measurement

The paper describes experiments concerning distance measurement with fiber-optic sensor and improvement of the measurement principle. The sensor probe was well-designed with a small structure and multi-function. The novel optical fiber probe arrangement as well as the possibilities of use for complex measurement problems are explained using the measurement of an internal screw thread as an example. The experimental results show that the measurement uncertainty of the thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.07%.     

基于labview与容栅传感器的液位测控系统

根据容栅传感器的检测原理,设计了一套基于LabVIEW和容栅传感器的液位精密测控系统,精度达0.05ml。利用容栅传感器输出的电容信号经信号调理模块输入msp430单片机处理并精密控制液位,采用LabVIEW设计系统监控界面程序,实现系统数据的显示、存储、绘图以及人机控制测定仪工作等功能。可配装为数显测定仪和物体密度测量仪,人机界面良好,成本低,易推广。     

Fiber-optic acoustic sensor for nondestructive evaluation

An experimental study was conducted to investigate the applicability of fiber-optic acoustic sensors to detect internal flaws in polymeric materials. A polarimetric fiber-optic sensor embedded in a plexiglass model received the acoustic signals generated by an ultrasonic transducer. It is shown that proper control of the polarization and phase of the optical beam is required to obtain meaningful results from the amplitude of the fiber-optic sensor signal. The sensor has shown promising results in determining acoustical properties of plexiglass and locating internal defects. The attractive feature of this sensing scheme is that the optical fibers are not modified prior to embedding. Therefore, they preserve their mechanical properties which makes the embedding process much easier.     

Fiber-optic vibration sensor system

A vibration measuring system based on a matched-fiber Bragg grating (FBG) is demonstrated, and the cross sensitivity of the temperature and strain was reduced by packaging the matched-sensing and interrogation FBG in the same shell, theory, system structure, and experimental results are presented. The experimental results demonstrated that the system has a good response to the 8–80 Hz vibration signal; it responds well to an acceleration of as low as 0.05 m/s², the system was deployed in a coalmine, and good experimental result were received. Because the system has the advantage of intrinsic safety and an easy multiplex, it has good prospects in the mining and petrochemical industry.     

Fiber-optic microbend sensor structure

We proposed and experimentally investigated a novel microbend sensor structure. The structure is composed of single-mode leads and multimode sensing fiber. The proposed structure exhibited a level of sensitivity as much as six times higher than that of the classical microbend sensor configuration when the same sensing fiber was used. Additionally, single-mode leads reduce lead noise and allow the use of more-coherent sources. The total loss of the proposed nondeformed structure is near 2 dB when the proper splicing method is used.     

Agile lensing-based non-contact liquid level optical sensor for extreme environments

To the best of the author's knowledge, demonstrated is the first opto-fluidic technology- based sensor for detection of liquid levels. An opto-fluidic Electronically Controlled Variable Focus Lens (ECVFL) is used to change the spatial intensity profile of the low power optical beam falling on the liquid surface. By observing, tuning and measuring the liquid surface reflected intensity profile to reach its smallest size, the liquid level is determined through a beam spot size versus ECVFL focal length calibration table. Using a 50 μW 632.8 nm laser wavelength liquid illuminating beam, a proof-of-concept sensor is tested using engine oil, vegetable oil, and detergent fluid with measured liquid levels over a 75 cm range. This non-contact Radio Frequency (RF) modulation-free sensor is particularly suited for hazardous fluids in window-accessed sealed containers including liquid carrying vessels in Electromagnetic Interference (EMI) rich environments.     

Fiber-optic temperature sensor using low-coherence interferometry

Low-coherence interferometric sensors are an important group of optical fibre sensors. Combining high measurement resolution with broad measurement range, these sensors can measure accurately several physical quantities e.g. temperature. In this article we present the fiber-optic temperature sensor using low-coherent interferometry, which has been designed and elaborated.     

Fiber-optic chemical sensor of amine-type compounds

A scheme of a fiber chemical sensor of amine-type compounds has been implemented. The sensor includes a film nanostructure deposited on the end face of an optical fiber 600 μm in diameter. The film consists of luminescent silica nanoparticles modified by functional pyrylocyanine dye, silver nanoparticles, and a photonic crystal opal film. An additional coating of the sensor film from above by a porous selective mirror, such as a photonic crystal, and introduction of silver nanoparticles 5–7 nm in diameter into it make it possible to increase the sensor sensitivity by an order of magnitude.     

Fiber-optic sensor design for chemical process and environmental monitoring

“Curing” is a term that is used to describe the cross-linking reactions in a thermosetting resin system. Advanced fiber-reinforced composites are being used increasingly in a number of industrial sectors including aerospace, marine, sport, automotive and civil engineering. There is a general realization that the processing conditions that are used to manufacture the composite can have a major influence on its hot–wet mechanical properties. This paper is concerned with the design and demonstration of a number of sensor designs for in situ monitoring of the cross-linking reactions of a commercially available thermosetting resin system. Simple fixtures were constructed to enable a pair of cleaved optical fibers with a defined gap between the end-faces to be held in position. The resin system was introduced into this gap and the cure kinetics were followed by transmission infrared spectroscopy. A semi-empirical model was used to describe the cure process using the data obtained at different cure temperatures. The same sensor system was used to detect the ingress of moisture into the cured resin system.     

Novel optical sensor for simultaneous measurement of liquid concentration and temperature

The paper describes a new optical sensor for simultaneous liquid concentration and temperature measurement. Temperature-dependent semiconductor absorption at the band edge is used as the principle of the temperature measurement, and the sensor exploits beam deviation caused by refraction due to the liquid concentration at the receiving end face of the optical device. The light intensity peak value and its deviation are detected by a charge-coupled device (CCD), and then the measured optical signal is reflected by a reflecting pyramid prism. The sensor probe is composed of an intrinsically pure GaAs single crystal, a reflecting pyramid prism, a partitioned water cell. Theoretical analysis and preliminary experimental results verify the feasibility of the proposed system.     

A new ultrasonic technique for the measurement of liquid level

A new design of pulse-echo ultrasonic liquid level gauge is described in which the ultrasonic pulse (here a Rayleigh or a Lamb wave) travels down a metal bar or strip towards the liquid surface, where, through a double mode-conversion process and a special reflecting structure, a strong echo is generated which travels back up the bar to the receiving transducer.The geometry of the special reflecting structure is outlined, and it is shown how this affects the basic accuracy of measurement. Inaccuracies arising from other effects like temperature variation, viscosity and poor signal-to-noise ratio are also discussed. Some mechanical variants, like using the wall of the tank in place of the metal bar carrying the ultrasonic wave and the use of corner reflectors as part of the reflecting structure, are also considered.A note in the Appendix briefly describes one method which has been used successfully for the generation of Rayleigh and Lamb waves.     

Fiber-optic sensor for the estimation of microbial corrosion of metals

This paper presents an optical approach to estimate the degree of corrosion of metals by measuring the changes in surface texture. The principle behind this method is based on scattering of light by objects. Source fiber is used to focus the light on the biocorroded metal surface. The resultant scattered and reflected light intensities are measured individually using detector fibers placed at different angles. The degree of corrosion is estimated as a ratio of scattered and reflected light intensities of specimen surface in a relative scale from 0 to 100. The observed optical measurements correlate well with the measured corrosion rate (correlation coefficient (R²)=0.972). A consistent relationship is found between optical measurements and corrosion levels.     

Fiber-optic extrinsic Fabry-Perot dc magnetic field sensor

We demonstrate a compact extrinsic Fabry-Perot interferometer-based fiber-optic sensor that uses magnetostrictive amorphous metallic wire Unitika AF-10 (Fe77.5B15Si7.5) as a sensor gauge for measuring dc magnetic fields. We present a theoretical model based on a Gaussian electric field distribution to analyze the sensor operation as a function of longitudinal air-gap separation. The model shows good agreement with the experimental results. A resolution of 50 nT over a range of 50-40,000 nT with a simple passive temperature-compensation method is obtained.     

Fiber-optic liquid-level sensor using a long-period grating

A liquid-level sensor based on the refractive-index sensitivity of long-period fiber-optic gratings is proposed and demonstrated. The form of the transmission spectrum of the long-period grating is dependent on the fraction of the length of the long-period grating that is surrounded by the liquid. The sensor shows a large linear range, with sensitivity of 4.8% change in transmission per millimeter, for a long-period grating with a length of 40 mm and a periodicity of 400mu;m .     

Fiber-optic curvature sensor with optimized sensitive zone

A novel fiber-optic sensor that can measure curvature directly has been developed previously. In this paper, the transduction of curvature to light intensity is described analytically by using the geometrical optics analysis. The mathematical model allows a quantitative optimization of the sensor without having to produce many sensors with slightly different combinations of parameters in order to accomplish a similar objective experimentally. The Monte Carlo simulation by ray tracing and an orthogonal matrix are used to optimize the fiber-optic sensor’s configuration. The results show that the depth of the sensitive zone and the number of teeth are two main parameters that affect the sensor’s sensitivity and the optimum number of teeth is 55, which is in agreement with the mathematical model.     

Design and operation of a fiber optic sensor for liquid level detection

Design and construction of an optical fiber sensor for liquid level detection are reported. This sensor operates based on light intensity modulation, and such modulation results from alteration of total internal reflection into partial reflection at the interface. The modulated intensity has been measured by using a pair of fibers, one transmitting source light, another acting as receiving fiber, and a glass prism providing the total and partial reflections. During the level measurements, when a liquid in a vessel touches the 45° faces of the 45-90-45° prism, the total internal reflection is disturbed, and the reflected light is modulated. The performance of this sensor is tested with different source lights including a light emitting diode (LED), a diode laser, and a He–Ne laser. Extinction ratio has been measured for different liquids, and compared. This ratio for water using LED source is about 0.03, for diode laser is 0.006 and for He–Ne laser is 0.003. Although this device was tested as a liquid level sensor, but the distinct results obtained for samples with different index of refractions demonstrate that the reported sensor can also be used as a liquid refractometer.     

一种基于电容传感器的液体密度测量电路的设计

设计了一种基于电容传感器的液体密度测量电路,介绍了设计思想和各部分的工作原理,给出了总的测量电路图.利用本电路测量相对误差在0.5%以内,具有测量准确度高、测量速度快、数字显示直读、使用简单的特点.     

以LNG为燃料的交通工具液位测量技术的发展

介绍了一些目前以LNG为燃料的交通工具常用的液位计,对其基本组成、基本工作原理以及发展动态进行了较为细致的分析和综述,根据以上因素对其优缺点进行了分析,为液位计的选择以及设计提供参考。同时也给出了除去液位计外影响液位测量精度的其他因素,为LNG燃料罐液位检测技术的研究方向提供参考。     

Fiber-optic dielectric multilayer temperature sensor: in situ measurement in vitreous during Er:YAG laser irradiation

A fiber-optic instrument for temperature measurement is presented. The sensing element consists of an optical dielectric multilayer system acting as a micro-interferometer which is deposited on a single-mode fiber tip. The sensitivity of the implemented system is theoretically derived and experimentally determined by a calibration measurement. The small size of the probe makes the system well-suited, for instance, for endoscopic in vitro and in vivo measurements in medical applications, especially in small samples. The sensor is used for the investigation of the transient thermal behavior of vitreous during Er:YAG laser irradiation in order to study the local thermal effects that are important to minimize the potential for unintentional injury in laser vitrectomy and laser vitreoretinal surgery.     

Fiber-optic polarimetric strain sensor with three-wavelength digital phase demodulation

A fiber-optic polarimetric strain sensor of l(S)=10-cm sensing length with three-wavelength passive quadrature digital phase demodulation is investigated. The demodulation unit uses a superluminescent diode light source with narrow-band interference filters in front of the photodiodes and real-time processing of the interference intensities by an arctan-phase-stepping algorithm. Quasi-static strain sensing is performed during slow periodic compression of a composite reinforced plastic rod with a sensor glued to its surface. The measured displacement sensitivity of delta?/deltal=125 mrad/mum, with a resistive strain gauge as a reference, agrees well with the value of 119 mrad/mum previously determined by fringe-distance measurement [Bock et al., Pure Appl. Opt. 5, 125 (1996)]. Despite a coherence-limited fringe contrast of only a few percent, a linearity of the phase-strain characteristic of the order of 1% and a strain resolution of 2.5muepsilon are demonstrated.