|Title:||High Accuracy Primary Laser Vibration Metrology at High Frequency Regimes|
|Objectives (recommended length: 2000-3000 char):|
International traceability to SI units is increasingly required by international standards, recommendations and regulations to ensure product quality, health and safety. Vibration and shock acceleration measurements are no exception. National Metrology Institutes (NMI) are currently active on assuring traceability of vibration and shock measurements to the SI units, upgrading or setting new standard methods for the vibration and shock calibration of transducers, improving the metrological basis. At the highest level, primary vibration calibration by laser interferometry is widely used.
The Primary vibration calibration of accelerometers is already standardized in ISO16063-11. This standard specifies the instrumentation and procedure to be used for primary vibration calibration of rectilinear accelerometers to obtain magnitude and phase lag of complex sensitivity by steady-state sinusoidal vibration and laser interferometry.
The increase of the excitation frequency to values higher than 5 kHz is another important topic of state-of-the-art research to improve capabilities and therefore, promote new operational activities in metrology. At this high frequency regime, 2 effects are of utmost importance when measuring vibrations, due to their high impact on accuracy performances of the system:
- Rocking motion effect;
- Mechanical coupling between laser table and shaker support.
The absolute calibration of accelerometers is based on the assumption that we can describe the accelerometer movement as purely axial and sinusoidal and that only one axis is necessary to characterize the movement. For a general rocking motion, we should take into account that the signal is integrated across the area of the accelerometer top face, thus averaging out any rotation of the device during signal acquisition due to the rocking motion of the shaker. In fact, shakers do not vibrate along one well defined and stable axis. We must assume a transverse displacement and accept a small rotation along axes perpendicular to the axial direction of the shaker. This rocking motion affects the estimation of the acceleration as measured interferometrically, projected along the direction of the laser beam.
This thesis will address these effects and improve several parts of the uncertainty budget. The main goals are:
- model & design the experimental setups for the measurement and characterization of the rocking motion effect;
- implement the full calibration chain comprising the interferometric systems, the shaker and accelerometer control, and the data acquisition/processing modules;
- analyse sensitivity to environment causes;
- validate & demonstrate performance of the system in international key comparisons.
With these objectives, we will be in position to promote a new national traceability chain in the accelerometers calibration field, allowing to extend the present measuring range and to bid successfully in a number of future international projects for metrological systems.
|Framework (recommended length: 500-2000 char):|
Measuring vibration is mandatory in our daily life, in different contexts as safety, process control, quality of life, work conditions, or preventive maintenance of industrial machinery. In a modern car the vibration triggers the airbags or the correct moment of ignition or fuel injection engine.
Vibrations are measured by accelerometers, based on a variety of physical principles. Calibration is mandatory and international standards exist to ensure traceability to primary standards.
In Portugal, the metrology of vibrations is handled by IPQ (Instituto Português de Qualidade), and in particular accelerometer primary calibration since 1998. Currently several laser vibrometry technologies to calibrate standards accelerometers exist, although the High Frequency regime (5 kHz) was still not possible to achieve with accuracies at the level of international NMI.
To overcome current limitation, it is fundamental to study, characterize and quantify effects like the rocking motion and the mechanical coupling between the laser table and the shaker using state-of-the-art optical techniques.
In this thesis, the synergies between the Laboratory of Optics Lasers and Systems from FCUL and the National Metrology Laboratory of IPQ will allow bridging the expertise on optical sensors and primary level metrology to extend country capabilities to worldwide level in vibration metrology.
A full calibration system based on optical instrumentation will be implemented and integrated in the IPQ calibration capabilities.
|Tasks (recommended length: 1000-3000 char):|
This thesis comprises 4 main tasks:
1 - Advanced methods for high accuracy displacement and angular metrology
2 - Modelling and Design
3 - Implementation of Calibration Chain
4 - Validation and Performance demonstration
In the first task 1 - "Advanced methods for high accuracy displacement and angular metrology", all the existing methods for optical metrology will be analyzed in view of the selection of the implemented technique.
In task 2 – “Modelling and Design”, the Shaker behaviour will be modelled and a complete uncertainty budget for the accelerometer calibration will be developed.
These models will generate theoretical ranges and resolutions for the experimental system to be implemented and the specification of all the required optical and mechanical components.
A general model of shakers must be developed. It may require data from optical measurements to have estimations of maximum translation or maximum angular deviation along/around different directions. Model will also benefit from data supplied by manufacturers and from information obtained within the network of NMI.
To measure movements associated to the rocking motion, an optical multi-channel system will be used, measuring displacement of several points. The interferometric system will also be modelled to complete the full system chain.
In task 3 – “Implementation of Calibration Chain”, all the hardware required for the calibration system will be designed (or re-designed for existing sub-systems), procured and implemented.
Task 3 will be the core of this project and will involve the design and integration of all the different blocks that build up the instrument required to perform the calibrations.This implementation comprises the optimization of the major blocks: the optical setup and the accelerometer/shaker subsystem. A prototype for a multi-channel system already exists in LOLS and it should be tailored for this particular application.
To calculate the acceleration based on the displacement value, it is necessary to implement data processing algorithms that take into account the specificity of each measuring system/method. All the different aspects of the signal analysis, data filtering and accelerations calculation will be studied. The algorithms will be developed and implemented in LabView.
Task 4 - “Validation and Performance demonstration”, comprises the validation of the mathematical model for the total uncertainty, the characterisation of the system in terms of the maximum frequency and minimum acceleration (for a given frequency) that can be realistically measured in view of a standard for calibration of accelerometers.
This task also includes the results validation by an international bilateral comparison (most probably in PTB, the German NMI, one of the world leaders in this field of metrology) or, if available during the time-frame of the thesis, participation in an international key comparison. This participation is done in the name of IPQ.
|Research centre/lab or R&D unit hosting the thesis project:|
|Laboratory of Optics, Lasers and Systems; of the Faculty of Sciences of the University of Lisbon|
|University to which the thesis project will be presented:|
|FC/UL - Faculdade de Ciências, Universidade de Lisboa|
|DAEPHYS Scientific Domain in which the project fits:|
|Relation of the project to the Scientific Domains of DAEPHYS:|
Metrology is the core of this project, more specifically fundamental primary metrology. The involvement of the IPQ, the Portuguese National Metrology Institute, ensures on the one hand that the top level requirements are in line with current needs defined at the highest level of Europe’s metrology institutes, and on the other hand the output of the projects as immediate application in the calibration activities of IPQ. In order to complete all the foreseen tasks, also domains like Instrumentation and Optical technologies will be part of the project and enrich this area of science that is floating in the interface between mentioned domains.
The candidate should master Physics Engineering and Optics: He will
1. model in detail all the sensing chain from the accelerometer to the interferometer, including the required signal conditioning and processing and the optical setup for the displacement measurement.
2. Design and implement the system for the calibration of primary standard accelerometers at high frequency.
3. Characterize and validate the performance of the system with the participation in international key comparisons.
|Does this proposal involve more than one University?:|
|Synergies between the two Universities participating in the proposal:|
|DAEPHYS strongly encourages the presentation of thesis projects in co-supervision by researchers from two of the universities participating in the Program. In this field, explain the benefits resulting from the proposed co-supervision and the involvement of elements from the two universities, e.g. building critical mass teams, profiting from existing infrastructures or advanced equipments, profiting from expert technical know-how, etc. If the proposal involves only one University, write n/a.|
|(recommended length: 500-1000 char)|
|Does this proposal involve a company?:|
|Proposals involving a company:|
|DAEPHYS strongly encourages the presentation of thesis projects involving a company, preferably a high-tech company. These proposals have to: 1) be centered on a technological problem in which the partner company has been (or plan / would like to be) involved; 2) have a co-supervisor on the enterprise; 3) include part of the project to be carried out in the company.|
|(recommended length: 500-1000 char)|
The IPQ’s National Metrology Laboratory (LNM) ensures the realization of all of the national standards of the measurement units of the International System (SI) base quantities and several SI derived quantities.
In the field of scientific metrology, the LNM has accompanied the main technical and scientific developments through the participation in European projects (framework of the European Metrology Research Programme), having submitted several applications also to European Metrology Programme for Research and Innovation. LNM has also participated in several interlaboratorial comparisons in order to ensure the traceability of measurements, as a NMI.
The proposed subject is a technological challenge of the utmost importance to extend the present range of measurement, considering high frequency values, enabling secure and ensure national traceability of magnitude acceleration.
The development and implementation of the experimental system will be carried out in IPQ facilities, Caparica.
|Name:||Alexandre Pereira Cabral|
|Institution:||Faculdade de Ciências da Universidade de Lisboa - FCUL|
|link to CV or indication of ORCID ID:|
|Name:||Maria Isabel de Araújo Godinho|
|Institution:||Instituto Português da Qualidade - IPQ|
|link to CV or indication of ORCID ID:|
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