H. Golnabi

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

Abstract 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.

Design and operation of different optical fiber sensors for displacement measurements

Design and operation of different intensity modulated extrinsic optical-fiber sensors are reported. A cantilever fiber-to-fiber, as well as a fiber-lens-fiber design is arranged and studied experimentally. The third scheme introduces a fiber-lens-double fiber design in which a double fiber is used for the light detection. In each case, a stepper motor driven micrometer system is used for the small displacement variations of the cantilever fiber or the ball lens. The results obtained for these sensors are checked against each other, advantages and disadvantages are explored, and the optimum sensor design for such a measurement is proposed.

A high precision method for measuring very small capacitance changes

A novel method for measuring very small capacitance changes based on capacitance-to-phase angle conversion is introduced in this article. This new method is the improved or linearized version of the nonlinear capacitance-to-phase angle conversion method. The main features of this scheme are the very good linearity, extremely high stray immunity and a very high resolution. The experimental results of the prototype version of this scheme have also been reported. By using this prototype and a simple capacitive transducer, a minimum detectable distance of about 16 nm can be achieved. This means that a capacitance change of about 0.7 fF (0.7×10−15 F) in a capacitance of 22 pF can be resolved, so the minimum resolvable relative capacitance is about 32 ppm. By the theory it can be seen that the minimum resolvable relative capacitance of 2 ppm could be achieved by this method.

FIBER OPTIC DISPLACEMENT SENSOR USING A COATED LENS OPTIC

Design and operation of an optomechanical displacement sensor employing a reflecting coated lens is reported. The light intensity modulation is based on the relative motion of the optical fibers and the lens. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. Displacement resolution of the order of 2.5 μm has been measured with a sensitivity of about 1.6 mV/μm for a dynamic range of 700 μm. The measured output is checked against the expected theoretical one and also other experimental results and good agreement are obtained.

Design and performance of an optical fiber sensor based on light leakage

Design and operation of an optical fiber sensor based on the light leakage from one fiber to another one causing intensity modulation are reported. Performance of this sensor is tested as a liquid level sensor for different liquids and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning sensor operation are described. The precision of measured values, reproducibility of the results (1.3%), and the stability of sensing operation as a function of time at different launching powers are also reported (0.8%). The reported results are promising and verify the successful operation of such a device as an on∕off level switch and also as a liquid level sensor.

DESIGN OF AN OPTICAL FIBER SENSOR FOR LINEAR THERMAL EXPANSION MEASUREMENT

Abstract Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV /° C for temperature detection and 7 μm /° C for thermal expansion detection. Device resolution for a linear expansion measurement is about 3 μm for a dynamic range of 600 μm corresponding to a temperature change of 100°C. The measured linear expansion results are checked against the expected theoretical ones and an agreement within ±2 μm is noticed. The operation of this sensor was also compared with other types and some advantages are observed, which verify the capability of this design for such precise measurements.

Mass measurement using an intensity-modulated optical fiber sensor

Design and operation of an opto-mechanical sensor for mass measurements is reported. This device uses a pair of optical fibers and a reflecting coated lens. The light intensity modulation is based on the relative motion of the lens due to a given mass with respect to the optical fibers. The modulated intensity because of the weighing mass has been measured by using a digital voltmeter. A full-range sensitivity of about 11.5 mV/g for a dynamic range of 80 g is obtained. A mass resolution of better than 0.25 g has been measured with this device. The measured output response is checked against the expected theoretical one and a general agreement observed. A comparison with similar experimental results shows some advantages of this method and potential use of such a sensor for medium mass measurements.

Design and operation of a laser scanning system

Design and operation of a laser scanning system based on a synchronized scanning geometry is described. Results for scanning plane and cylindrical surfaces are reported. Deviations of the experimental results from that of the expected theoretical ones are presented. The described system offers a good reproducibility and results agree well with the theory. The results obtained from our system are satisfactory and show a promise in order to be used in the real applications. The reported approach can also be used in the design of a three-dimensional vision system.

Role of laser sensor systems in automation and flexible manufacturing

Abstract New industries and production plants require a flexible system, which is capable of picking up objects of various shapes, weights, and colors with arbitrary position and orientation. Such a system also needs recognition and guiding sub-systems. The recognition system includes target function for the recognition sub-system and relation between object characteristics and recognition target. The laser sensor system can be used for such object recognition. Wire-based telemetry and control systems can cause many problems in shop floors and factories, and so there has been a strong growth of interest in wireless guidance like vehicles equipped with laser guiding and navigation systems. For the continuous measurements of parameters such as temperature, etc. optical laser sensor technology seems to become more applicable at this stage. This article describes the operational principles and the use of the most advanced laser sensor systems for quantity measurements, guiding, navigation, pattern recognition, and vision systems for inspection purposes. A variety of laser-based sensors, which can be used as sensing devices in manufacturing, and production technology, are described in this study. Adaptive cruise control systems that can be used in automobile industry to monitor distance and speed are described in this report. As a typical example, the principal operation of a laser guided mobile robot using a laser navigation system is also described.

Simulation of interferometric sensors for pressure and temperature measurements

A Mach–Zehnder type fiber optic sensor is modeled and the phase change for this device as a result of pressure or temperature variation is studied. Different parameters involved in the sensing process such as Youngs modulus, Poissons ratio, light wavelength, index of refraction, and stress–optic coefficients are changed and their effects investigated. Our results show that Youngs modulus, Poissons ratio, light wavelength, and stress–optic coefficients have the major roles for pressure sensing. On the other hand for temperature sensing, light wavelength, thermal expansion coefficient, and temperature dependence of the index of refraction are the important parameters. For a typical silica glass fiber at 0.6328 μm wavelength, the calculated phase change due a pressure change of 1 Pa for the 1 m length is 4.08×10−5 rad. This phase change for 1 m of a similar probe fiber corresponding to 1 °C temperature change is found to be 107 rad.