Metrological characterisation of Low Power Voltage Transformers by using impulse response analysis

this thesis presents a new approach in dealing with characterize LPVT and proposes determining the impulse response of LPVT, purposing to find transfer function (h(t)) which contains most electrical characteristics of LPVTs as a dynamic system

Bond graph simulation of error propagation in position estimation of a hydraulic cylinder using low cost accelerometers

The indirect calculation from acceleration of transversal displacement of the piston inside the body of a double effect linear hydraulic cylinder during its operating cycle is assessed. Currently an extensive effort exists in the improvement of the mechanical and electronic design of the highly sophisticated MEMS accelerometers. Nevertheless, the predictable presence of measurement errors in the current commercial accelerometers is the main origin of velocity and displacement measurement deviations during integration of the acceleration. A bond graph numerical simulation model of the electromechanical system has been developed in order to forecast the effect of several measurement errors in the use of low cost two axes accelerometers. The level of influence is assessed using quality indicators and visual signal evaluation, for both simulations and experimental results. The obtained displacements results are highly influenced by the diverse dynamic characteristics of each measuring axis. The small measuring errors of a simulated extremely high performance sensor generate only moderate effects in longitudinal displacement but deep deviations in the reconstruction of piston transversal movements. The bias error has been identified as the source of the higher deviations of displacement results; although, its consequences can be easily corrected.Peer ReviewedPostprint (published version

ANALYSIS AND APPLICATION OF CAPACITIVE DISPLACEMENT SENSORS TO CURVED SURFACES

Capacitive displacement sensors have many applications where non-contact, high precision measurement of a surface is required. Because of their non-contact nature they can easily measure conductive surfaces that are flexible or otherwise unable to be measured using a contact probe. Since the output of the capacitance gage is electrical, data points can be collected quickly and averaged to improve statistics. It is often necessary for capacitive displacement sensors to gage the distance from a curved (non-flat) surface. Although displacements can easily be detected, the calibration of this output can vary considerably from the flat case. Since a capacitance gage is typically factorycalibrated against a flat reference, the experimental output contains errors in both gain and linearity. A series of calibration corrections is calculated for rectifying this output. Capacitance gages are also limited in their overall displacement travel. A support stage is described that, along with control electronics, allow the properties of the capacitance gage to be combined with an interferometer to overcome this displacement limitation. Finally, an application is proposed that would make use of the capacitance sensor and support stage assembly

Spacetime Metrology with LISA Pathfinder

LISA is the proposed ESA-NASA gravitational wave detector in the 0.1 mHz - 0.1 Hz band. LISA Pathfinder is the down-scaled version of a single LISA arm. The arm -- named Doppler link -- can be treated as a differential accelerometer, measuring the relative acceleration between test masses. LISA Pathfinder -- the in-flight test of the LISA instrumentation -- is currently in the final implementation and planned to be launched in 2014. It will set stringent constraints on the ability to put test masses in geodesic motion to within the required differential acceleration of 3\times10^{-14} m s^{-2} Hz^{-1/2} and track their relative motion to within the required differential displacement measurement noise of 9\times10^{-12} m Hz^{-1/2}, around 1 mHz. Given the scientific objectives, it will carry out -- for the first time with such high accuracy required for gravitational wave detection -- the science of spacetime metrology, in which the Doppler link between two free-falling test masses measures the curvature. This thesis contains a novel approach to the calculation of the Doppler response to gravitational waves. It shows that the parallel transport of 4-vectors records the history of gravitational wave signals. In practice, the Doppler link is implemented with 4 bodies in LISA and 3 bodies in LISA Pathfinder. To compensate for noise sources a control logic is implemented during the measurement. The closed-loop dynamics of LISA Pathfinder can be condensed into operators acting on the motion coordinates, handling the couplings, as well as the cross-talks. The scope of system identification is the optimal calibration of the instrument. This thesis describes some data analysis procedures applied to synthetic experiments and shows the relevance of system identification for the success of LISA Pathfinder in demonstrating the principles of spacetime metrology for all future space-based missions.Comment: PhD thesis defended at University of Trento on 26th March 2012. Advisors: Stefano Vitale, Mauro Hueller. Committee: Eugenio Coccia (Univ. of Rome, Tor Vergata), Philippe Jetzer (Univ. of Z\"urich), Eric Plagnol (APC-CNRS, Paris), Rita Dolesi (Univ. Of Trento

Development and Experimentation of Traceable Characterization Methods for Medium Voltage Instrument Transformers for PQ and PMU Applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Design, manufacture and test of a magnetic encoder

An new eddy current based magnetic position encoder structure is proposed and studied in this thesis. The encoder is composed of one read head and one scale with metal plates placed periodically on a substrate. The read head contains one emitter and two receiver pairs which are all rectangular planar coils. The electromagnetic coupling between the emitter and receivers were affected by the relative position of the scale. A system level analytical model of the proposed encoder structure has been derived, from which three different encoder signals forms were generated. An amplification and synchronous demodulation circuit has been designed and fabricated. The circuit board was used successfully to process the encoder output signals in the measurement. Four PCB encoder prototypes were fabricated. These encoder structures were studied using the ANSYS MaxwellTM software package. The simulated and measured results were compared. The best accuracy performance of the PCB encoder is -15 μm to 15 μm from the simulation results and -35 μm to 25 μm from the corresponding measurement. An alternative manufacturing process of the magnetic encoder based on multilayer Low Temperature Co-fired Ceramic (LTCC) technology has also been presented. The fabrication process of the LTCC encoder and equipment used were described. Two different methods were used to characterise the LTCC encoder with good agreement between all approaches attempted. The best accuracy performance of the LTCC encoder was -30 μm to 25 μm and after lookup table correction the improved accuracy ranged from -10 μm to 10 μm

CAPACITANCE METROLOGY OF CURVED SURFACES: STUDY AND CHARACTERIZATION OF A NOVEL PROBE DESIGN

Capacitive sensors are frequently applied to curved target surfaces for precision displacement measurements. In most cases, these sensors have not been recalibrated to take the curvature of the target into consideration. This recalibration becomes more critical as the target surface becomes smaller in comparison to the sensor. Calibration data are presented for a variety of capacitance probe sizes with widely varying geometries. One target surface particularly difficult to characterize is the inner surface of small holes, less than one millimeter in diameter. Although contact probes can successfully measure the inner surface of a hole, these probes are often fragile and require additional sensors to determine when contact occurs. Probes may adhere to the wall of the hole, and only a small number of data points are collected. Direct capacitance measurement of small holes requires a completely new capacitance probe geometry and method of operation. A curved, elongated surface minimizes the gap between the sensor surface and the inner surface of the hole. Reduction in the size of the sensing area is weighed against electronics limitations. The performance of a particular probe geometry is studied using computer simulations to determine the optimal probe design. Multiple, overlapping passes are deconvolved to reveal finer features on the surface of the hole. A prototype sub-millimeter capacitance probe is machined from tungsten carbide, with four additional material layers added using ebeam deposition. Several techniques are studied to remove these layers and create a sensing area along one side of the probe. Both mechanical processes and photolithography are employed

Force Measuring System for High-Precision Surface Characterization under Extreme Conditions

Force measuring is used in various surface characterization techniques such as indentation, scratch tests, tribological analysis, determination of gas content, etc. The main problems related with force measurement under extreme conditions have been analysed. A strategy that should be followed to solve these problems has been discussed and several examples of successive solutions that recently were developed by the authors are presented. The need to carry out the characterization under extreme conditions poses serious problems for the designers of the measuring systems that may include the incompatibility of the sensors with the test conditions, undesirable interactions with other components, stability, precision and uncertainty issues, the measurement range, etc. Resolving these problems must be based on a global approach in which the characterization system is considered as a whole, while the designer must analyse and solve the possible conflicts between the subsystems. The way how an appropriate force measuring system can be selected is described. The proposed method is illustrated by an example in which an indirect force measurement using optical fibre displacement sensor was used. Another example describes measuring system developed for vacuum high-temperature nanoindentation. At high temperature, proper heat management based on non-contact heating and laminar flow cooling system is mandatory to avoid experimental data being affected by external noise and thermal drift

A Soft Multiple-Degree of Freedom Load Cell Based on The Hall Effect

The goal of this thesis is to develop a soft multiple-degree-of-freedom (multi-DOF) load cell that is robust and light weight for use in robotics applications to sense three axes of force and a single axis of torque. The displacement of the magnet within the elastomer changes the magnetic flux density which is sensed by two 3-axis Hall effect sensors. Experimental measurements of magnetic flux density within the area of interest were used to formulate analytic expressions that relate magnet field strength to the position of the magnet. The displacement and orientation measurement and the material properties of the elastomer are used to calibrate and calculate the applied load. The ability to measure 3-DOF force and axial torque was evaluated with combined loading applied by a robotic arm (KUKA, LBR r820 iiwa). The decoupled results show the 4-DOF load cell was able to distinguish 3-axis force and 1-axis torque with 6.9% averaged error for normal force, 4.3% and 2.6% for shear force in the X and Y axis and 8.6% for the torque. The results show good accuracy for a soft multi-axis sensor that would be applicable in many robotic applications where high accuracy is not required