Differential Measurement Method Research Articles

High Precision Robust Automatic Alignment Method for Rotating Shaft

Rotating Shaft is widely used in various high precision instruments on scientific and industrial metrology. This paper proposes a high precision and robust method to automatically align a rotating shaft perpendicular to the horizontal plane. Firstly, an alignment model consisting of a dual-axis inclinometer and four motors is designed. Then the rotating shaft tilt angle between the practical and the ideal shaft is projected to two orthogonal planes, and generates a rotation angle in each plane. The two rotation angles are calculated by differential measurement method based on the inclinometer outputs, and then the relationship of shaft tilt angle against inclinometer outputs is obtained. According to these two rotation angles, the relative heights of the three supporting points of the platform attached to the rotating shaft are calculated. Employing an angle closed loop strategy; the rotating shaft tilt angle is aligned by three linear stepping motors. Experiment results show an alignment precision of 0.003o is achieved using an inclinometer with the resolution of 0.0005o and a linear stepping motor with the regulation precision of 0.89 μm. The proposed method is suitable for a wide variety of precision machines that require the use of rotating shaft.

Laser multi-reflection differential confocal long focal-length measurement.

We propose a new laser multi-reflection differential confocal focal-length measurement (LDCFM) method to meet the requirements of high-precision measurements of long focal lengths. An optical flat and a reflector are placed behind a test lens for reflecting the measuring beam repeatedly. Then, LDCFM uses the property that the null points of differential confocal response curves precisely correspond to the convergence points of the multi-reflected measuring beam to exactly determine the positions of the convergence points accurately. Subsequently, the position variation of the reflector is measured with different reflection times by using a distance-measuring instrument, and thereby the long focal length is measured precisely. Theoretical analyses and preliminary experimental results indicate that the LDCFM method has a relative expanded standard uncertainty (k=2) of 0.04% for the test lens with a focal length of 9.76m. The LDCFM method can provide a novel approach for high-precision focal-length measurements.

AMPEROMETRIC MULTIBIOSENSOR SYSTEM WITH DIFFERENTIAL MODE OF MEASUREMENT OF CURRENTS

A possibilities of increasing the sensitivity and immunity amperometric biosensor systems by applying the differential method of measurement have been discussed. The structural and algorithmic solutions are proposed for reducing the impact of existing sources of errors in the measuring channel. The potentiostat for amperometric multibiosensor system with differential mode of measurement and automatized adjusting has been developed. The suppression of common mode noise on the differential sensor was experimentally investigated.

Laser differential confocal radius measurement method for the cylindrical surfaces.

This paper proposes a laser differential confocal cylindrical radius of curvature measurement (DCCRM) method for high accuracy measurement of the radius of curvature of the cylindrical lens. Based on the property that the null point of an axial intensity curve precisely corresponds to the focus of the objective in a differential confocal system (DCS), the DCCRM uses the null point of the DCS axial intensity curve to precisely identify the cat's eye position and confocal position of the test cylindrical lens. The distance between the two positions is measured accurately using a laser distance instrument, thus achieving high precision radius measurement. In comparison with existing measurement methods, the proposed DCCRM has high measurement precision and strong environmental anti-interference capability. Theoretical analyses and preliminary experimental results indicate that the DCCRM has a relative measurement uncertainty of better than 0.03% and provides a new approach for a high precision radius measurement of the cylindrical lens.

Research on Three-Component Geomagnetic Field Differential Measurement Method for Underwater Vehicle

Research on Three-Component Geomagnetic Field Differential Measurement Method for Underwater Vehicle

Double-core optical waveguides fabricated by astigmatic femtosecond Bessel beam in silica glass

In this paper, a collimated femtosecond Gaussian beam with a central wavelength of 800 nm and a pulse duration of 50 fs is converted into a Bessel beam by an axicon with an apex angle of 140. By adjusting the femtosecond Gaussian beam incidence angle on the axicon, both anastigmatic and astigmatic femtosecond Bessel beams can be generated. Single- and double-core optical waveguides are fabricated in silica glass respectively by using anastigmatic and astigmatic femtosecond Bessel beams. Anastigmatic femtosecond Bessel beams with different single pulse energies (0.39 mJ and 0.47 mJ) are employed to fabricate the single-core optical waveguides in silica glass. The fabricated single-core waveguide's core diameter and refraction index change are found to be dependent on both the single pulse energy and pulse number used to fabricate the waveguide. By rotating the axicon, femtosecond Bessel beam with astigmatism is generated, which is used to fabricate double-core optical waveguides in silica glass. In the experiments 50 fs laser pulses with single pulse energy of 0.36 mJ are employed to fabricate the double-core optical waveguide. Experimental results show that when the rotation angle of the axicon is relatively small (1), i.e., the incidence angle of the femtosecond Gaussian beam on the axicon is 89, the distance between the two cores of the fabricated double-core waveguide is only 5.6 m. In this case the energy ratio of the coupled He-Ne laser between the two cores varies periodically as the waveguide's position changes towards one specific direction. When the axicon is rotated 3 and 5, the distances between the two cores increase respectively up to 9.1 m and 16.1 m, and no periodic variation of the coupled light energy ratio between the two cores is observed. It is inferred that the waveguides fabricated using the axicon with rotation angles of 3 and 5 are in fact optical waveguides with double parallel cores. According to the experimental results shown above, it is deduced that the double-core optical waveguide can be used as a highly sensitive differential displacement sensor, and the minimal detectable displacement is found to be less than 3 m. The light energy difference between the two cores is used to measure the displacement, so the displacement sensor made by double-core optical waveguide is a kind of differential detector with a higher signal-to-noise ratio than the frequently-used single-core waveguide displacement sensor. In addition, because the core zone of the double-core waveguide is composed of two cores separated by a distance which can be changed by adjusting the angle of the axicon before the fabrication process, the resulting larger core zone greatly facilitates the assembly process of the displacement sensor while the high detection sensitivity of the displacement is simultaneously achieved due to the using of the differential measurement method.

Brillouin optical time-domain analysis sensor assisted by Brillouin distributed amplification of pump pulses.

We demonstrate the extension of the measurement range of Brillouin optical time-domain analysis (BOTDA) sensors using a distributed Brillouin amplifier (DBA). The technique is based on injecting a DBA pump wave in the fiber to generate an additional Brillouin interaction that amplifies the BOTDA pump pulses and compensates optical fiber attenuation. This amplification does not introduce any significant noise to the BOTDA's probe wave due to the inherent directionality of the Brillouin gain. Additionally, we deploy a differential pulse-width pair measurement method to avoid measurement errors due to the interplay between the self-phase modulation effect and the changes in the temporal shape of the pulses induced by the transient behavior of Brillouin gain. Experimental proof-of-concept results in a 50-km fiber link demonstrate full compensation of the fiber's attenuation with no penalty on the signal-to-noise ratio of the detected signal.

Laser reflection differential confocal large-radius measurement.

A laser reflection differential confocal large-radius measurement (RDCLRM) method is proposed to meet the requirements of high-precision measurement for a large radius of curvature (ROC). The RDCLRM identifies the converging point of the multiply reflected test beam by using the differential confocal focusing technology. It then measures the distance between the positions of the test lens corresponding to these converging points for different reflection times. Therefore, a precise and high-efficiency measurement of a large ROC is achieved with a shorter measurement lightpath. The theoretical analyses and preliminary experimental results indicate that RDCLRM has a relative expanded uncertainty of better than 0.005% (k=2).

Differential Thickness Layer Resistance Measurement method for measurements of contact resistance of organic semiconductor thin films

The objective, basic theory and application of a new DTLRM (Differential Thickness Layer Resistance Measurement) method of contact resistance Rc (resistance of interface) and contact resistivity measurements are described. The method was developed for ultrathin films of high-ohmic organic semiconductors. The method is based on measurements of total resistance RT,1, RT,2 between two opposite planar contacts on two samples of differing thickness L1, L2 prepared from the same organic semiconductor. The important requirements are that both the opposite contacts are ohmic, that linear dimensions of the contacts are much larger than the film thickness, and that the actual measured data are consistent in the sense of condition 1<RT,2/RT,1<L2/L1. The DTLRM method was verified on zinc phthalocyanine samples with Au and Pt contacts. If the basic assumptions are fulfilled, the DTLRM method can be applied to a broad range of high-ohmic thin films.

Large-aperture laser differential confocal ultra-long focal length measurement and its system.

A new laser differential confocal ultra-long focal length measurement (LDCFM) method is proposed with the capability to self-calibrate the reference lens (RL) focal length and the axial space between the test lens and RL. Using the property that the focus of laser differential confocal ultra-long focal length measurement system (LDCFS) precisely corresponds to the null point of the differential confocal axial intensity curve, the proposed LDCFM measures the RL focal length f(R)' by precisely identifying the positions of the focus and last surface of RL, measures the axial space d(0) between RL and test ultra-long focal length lens (UFL) by identifying the last surface of RL and the vertex of UFL last surface, and measures the variation l in focus position of LDCFS with and without test UFL, and then calculates the UFL focal length f(T)' by the above measured f(R)', d(0) and l. In addition, a LDCFS based on the proposed method is developed for a large aperture lens. The experimental results indicate that the relative uncertainty is less than 0.01% for the test UFL, which has an aperture of 610 mm and focal length of 31,000 mm. LDCFM provides a novel approach for the high-precision focal-length measurement of large-aperture UFL.

High accuracy differential pressure measurements using fluid-filled catheters – A feasibility study in compliant tubes

High accuracy differential pressure measurements are required in various biomedical and medical applications, such as in fluid-dynamic test systems, or in the cath-lab. Differential pressure measurements using fluid-filled catheters are relatively inexpensive, yet may be subjected to common mode pressure errors (CMP), which can significantly reduce the measurement accuracy. Recently, a novel correction method for high accuracy differential pressure measurements was presented, and was shown to effectively remove CMP distortions from measurements acquired in rigid tubes. The purpose of the present study was to test the feasibility of this correction method inside compliant tubes, which effectively simulate arteries. Two tubes with varying compliance were tested under dynamic flow and pressure conditions to cover the physiological range of radial distensibility in coronary arteries. A third, compliant model, with a 70% stenosis severity was additionally tested. Differential pressure measurements were acquired over a 3cm tube length using a fluid-filled double-lumen catheter, and were corrected using the proposed CMP correction method. Validation of the corrected differential pressure signals was performed by comparison to differential pressure recordings taken via a direct connection to the compliant tubes, and by comparison to predicted differential pressure readings of matching fluid–structure interaction (FSI) computational simulations. The results show excellent agreement between the experimentally acquired and computationally determined differential pressure signals. This validates the application of the CMP correction method in compliant tubes of the physiological range for up to intermediate size stenosis severity of 70%.

Influence of deposition conditions on electrical and mechanical properties of Sm2O3-doped CeO2 thin films prepared by EB-PVD (+IBAD) methods. Relationship between investigated film and substrate at indentation

The study of polycrystalline CeO2 + xSm2O3 (x = 0, 10.9–15.9 mol %) thin films deposited by Electron Beam Physical Vapour Deposition (EB-PVD) and Ionic Beam Assisted Deposition (IBAD) techniques on the Si substrate was devoted to the influence of deposition conditions used, namely composition x, deposition temperature Tdep and Ar+ ion bombardment as well as the structure and (micro)structure on the (micro)hardness H using the differential hardness, Hdif, as a parameter. The investigations were made using, as in our recent papers, the depth sensing indentation (DSI) technique. The study was focused on the depth dependence of the film/substrate system response on the indentation response from the surface of films up to the film/substrate interface. This study has shown that the critical indentation depth, where the influence of substrate is negligible, can be observed for some CeO2 films doped with Sm2O3 as well as for undoped CeO2 films, both deposited at Tdep = 200°C without IBAD as well as using IBAD. Besides it, a wavy character of differential curve due to the inhomogeneities of films was observed with good reproducibility at some films. It was proven, that the method of differential hardness measurement is applicable for the determination of critical indentation depth as well as for the study of microstructure response of thin films from the film surface up to the film/substrate interface. Results of this study are described and discussed.

A Differential Measurement Method for Solving the Ephemeris Observability Issues in Autonomous Navigation

The autonomous navigation of navigation and positioning systems such as the Global Positioning System (GPS) and other Global Navigation Satellite Systems (GNSS) was motivated to improve accuracy and survivability of the navigation function for 180 days without ground contact. These improvements are accomplished by establishing inter-satellite links in the constellation for pseudo-range observations and communications between satellites. But observability issues arise for both ephemeris and clock since the pseudo-range describes only the relative distance between satellites. A differential measurement method is proposed to measure the rotation of the constellation as a whole for the first time. The feasibility of the proposed method is verified by simulations.

Surface tension of dimethyl ether in the temperature range 120–214 K

The capillary constant a 2 was measured by the differential capillary method of surface tension measurement. The surface tension σ of dimethyl ether was calculated. The experiments were performed both above the triple point temperature (T t = 131.66 K) and below it in the range in which the coexisting liquid and gas are metastable. Equations that approximate the temperature dependences of a 2 and σ were suggested. The excess surface entropy and energy were determined. The surface entropy had a maximum at T ≈ 190 K.

Self-sensing control of piezoelectric positioning stage by detecting permittivity

Piezoelectric displacement contains hysteresis and creep properties. Therefore, a displacement sensor is indispensable in precise positioning devices; however, the additional space and cost are problems. On the other hand, self-sensing methods that utilize the piezoelectric actuator itself as the displacement sensor have been proposed. With these self-sensing methods, precise positioning becomes possible without an additional displacement sensor. We developed a self-sensing method utilizing the non-hysteresis relationship between the permittivity change and the piezoelectric displacement. Furthermore, a differential current measurement method using two piezoelectric elements with a bimorph actuator could improve the positioning accuracy. In this study, we examine the control of a positioning stage using two multilayered piezoelectric actuators by applying the differential current measurement method for self-sensing control. The results indicate that the differential current measurement method is effective for precise positioning control. The positioning errors due to hysteresis decreased from 0.8μm to 0.1μm for a 10μm displacement range. In addition, permittivity feedback control could compensate for the creep property.

Fourier-domain mode delay measurement for multimode fibers using phase detection

We have proposed a powerful method based on a phase detection reflectometric technique to solve the difficulty of the small signal discrimination in the amplitude-detection method for differential modal delay measurement of multimode optical fibers (MMFs). The phase is radically shifted to π at the time delay positions among the excited modes even when the amplitudes of the peaks cannot be distinguished with the noise level. The modal dispersion of the MMF under test can be simply determined by choosing the time delay in the last phase shift in the Fourier domain. In addition, we confirmed that the phase-sensitive interferometric measurement does not need to scramble the excited modes in the fiber. We subsequently conclude that a portable modal dispersion or mode analysis equipment can be developed by using the phase-detection intermodal interferometric technique proposed here.

A Novel Floor Sensor Network Technology Based on Dielectric Electro-Active Polymers

This study describes a novel floor sensor network being developed to provide a competitive and universal pressure mapping technology for a wide range of medical, research and security applications. The presented sensor network consists of 16 sensor elements distributed in a 4x4 sensor matrix. The sensor elements are made of a special dielectric electro-active polymer film being capable of capacitive sensing of the surface pressure. Each sensor unit is 200x160 mm resulting in an overall sensor matrix size of 800x740 mm. A high precision and high speed sensor interface was realized to provide a differential capacitance measurement method fulfilling the specific measuring requirements of the sensor matrix. Based on the measurement results, the developed sensor network is capable of measuring the distributed weight on their surface with an accuracy of 5 kg, however, this initial measuring accuracy can be significantly increased by improving the manufacturing technology of the sensor elements.

In-Depth Research Information Differential Method of Measurement

With the development of automation and communication technology, measurement information is widely used in various industrial, agricultural, commercial, and other living. At present, the problems exist in the accuracy and time synchronization of the measurement information. That brings the difficulty for data analysis and decision making. This paper starts from the existing measurement information, in-depth analyses the root cause, puts forward the measurement information of differential method, the effect of practical application in electric power system by measuring the differential method of information So as to determine the role of differential measurement method of information and promotion value, provide strong support for the rapid development of automation information technology.

LSPR Sensor Combining Sharp Resonance and Differential Optical Measurements

A new optical sensor based on the localized surface plasmon resonance (LSPR) in 2D arrays of silver nanoparticles (AgNPs) combined with a differential optical measurement method is developed. LSPR substrates comprised of self-assembled, 2D arrays of AgNPs exhibit coherent plasmon coupling manifested as a sharp peak in the blue spectral region. A bottom-up approach was used to fabricate reproducible and cost-effective substrates with a figure of merit (FOM) of ~24. The LSPR shift was determined by measuring the difference between light extinction at two wavelengths selected on each side of the sharp peak. The sharpness of the coherent plasmon resonance together with the differential measurement method enabled a record sensing resolution in bulk for a LSPR sensor of ~4.8E-6 RIU.

An Ultrasonic Fuel Identification System for Liquid Metal Cooled Reactors Resilient Against Multiple Transducer Failures

We describe a fuel assembly identification system developed for the MYRRHA reactor-a new multi-purpose flexible irradiation facility to replace the aging BR2. MYRRHA is a fast spectrum research reactor cooled with lead-bismuth eutectic (LBE) and conceived as an accelerator driven system capable of operating in sub-critical and critical modes. As liquid metal is opaque to visual light, the conventional optical fuel assembly identification system, as used by water cooled reactors, has to be replaced by a system not hindered by the opacity of the coolant. As already suggested in the late sixties, we use ultrasound for this purpose and present an encoding especially designed to enhance the robustness of the ultrasonic read-out. The encoding is based on notches of varying depth on the inflow nozzle of a fuel assembly. The depth of each notch is used to encode two bits and is measured by a dedicated transducer aligned over the notch. To increase the reliability of the fuel identification process, the identification number is protected by an error correcting code based on Hamming codes. We describe the ultrasonic system used to read out the vector of depths which is subsequently converted to a vector of bits. We explain the encoding of the twelve bit fuel identification numbers to a 22-bit error correcting code and discuss how Hamming decoding can be used to correct single bit errors, detect two bit errors or fill in the missing bits of a failing transducer. We shortly show how the confidence on the individual measurements can be taken into account using a Gaussian measurement error distribution assumption. We also present a method based on solving a linear system over Boolean variables to (partially) reconstruct the fuel identification number in case multiple transducers fail. We show that the probability on full reconstruction is 100% for up to two transducer failures, 98% for three, 79% for four and 20% for five failing transducers. Finally, we prese- t validation results in water and lead-bismuth eutectic for the differential measurement method used to measure the depth of the notches which form the basis for the requirements of the final system which will be installed on a robotic fuel manipulator.