Research in the Mechanical Metrology Area
This page contains more information for the following projects:
- Uncertainty Quantification
- Effect of homodyne interferometer nonlinearities on the complex sensitivity calibration of accelerometers
- SADC comparisons in the field of length
- Dimensional traceability in nanometrology
- Provide Mass and Volume training to SADC metrologists
Effect of homodyne interferometer nonlinearities on the complex sensitivity calibration of accelerometers
Research has been conducted to determine nonlinearities of laser (homodyne and heterodyne) interferometers in displacement measurement (length) applications. These nonlinearities are in the order of nanometers.
Internationally, the standard for vibration is mostly realised in compliance with ISO 16063 part 11 and more recently, applied in compliance with part 41 of the standard. Implementing this standard, using the Sine Approximation Method (SAM), displacements in the order of nanometers are measured in the field of vibration metrology for frequencies above 5 kHz, using laser interferometry. This is used to determine the complex (magnitude and phase) response of vibration measuring devices (accelerometers and laser vibrometers).
Different NMIs are focussing on different aspects of improving/extending vibration standards. The current norm is magnitude calibration from 10 Hz to 10 kHz, with only two NMIs (NMISA & PTB) having CMCs for complex calibrations. Research is focused on techniques to extend the frequency range by the PTB (Germany) and CENAM (Mexico). However, phase calibrations are relatively new in this area, and have not been extensively researched. It is thus an ideal research opportunity to contribute to the International pool of knowledge. Research will be conducted to determine the magnitude of errors, as a result of nonlinearities in laser interferometers, when measuring rectilinear displacements using homodyne laser interferometry with a quadrature detection system. The effect of the nonlinearities on the magnitude and phase (complex displacement) measurements will be investigated.
Two main causes of nonlinearities in said interferometers will be investigated:
- Nonlinearities introduced by imperfect optical equipment
- Nonlinearities as a result of imperfect alignment of the optical equipment.
The research will be presented as part of a Doctorate study at the Tshwane University of Technology.
For more details, contact Mr. Ian Veldman.
SADC comparisons in the field of length
The project is being conducted by the dimensional metrology laboratory. The project aims to assist with further developing the capability of the SADC metrology institutes in the field of length. Initially, two comparisons are planned.
The two parameters under consideration will be
- Steel rules. These instruments are the National standard for length in many SADC countries
- Gauge blocks. These instruments are most commonly used as standards in the manufacturing industry.
These two comparisons were proposed at the last CCL meeting and accepted as comparisons in the SADCMET region.
For more details, contact Mr. Oelof Kruger.
Dimensional traceability in nanometrology
Nanometrology is an indispensable part of Nanotechnology. Nanotechnology applications are vast, and one of the fields being receiving much attention is energy, where natural energy sources are being investigated as an alternative to fossil fuels. Research is currently being conducted to use hydrogen gas as a fuel source for automobiles. Nanomaterials such as nanotubes are being investigated for their potential use in the storage of hydrogen.
For the nanotubes to function effectively as a storage medium, their properties and size need to be well understood. Microscopes such as the Atomic Force Microscope (AFM) are used as quantitative measurement instruments for nanotubes. Consequently there is a high demand for standardization and calibration for AFM’s. The project will continue work initiated in 2006/7. It is planned that lateral standards measured in 2006/7 will be measured again using an AFM from PTB (Physikalisch-Technische Bundesanstalt) Germany. The results will be compared and this will assist in establishing traceability for these standards. In addition, a proficiency scheme is planned, which will involve measurements of AFMs throughout South Africa.
An optical diffraction technique for the measurement of gratings is an inexpensive method that can be employed in establishing traceability for lateral calibration of AFM. The project aims to build such an optical diffraction system pending acquisition of a metrology-grade AFM for the NMISA.
For more detail contact Mr. Sam Thema.
Provide Mass and Volume training to SADC metrologists
The project aims to develop staff of SADC National Measurement Institutes in the fields of mass and volume. Training will be conducted in both fields, and will include theory and practical exercises.
For SADCMET to be recognized internationally, it has to ensure that the National Measurement Institutes have metrologists with the necessary training and experience to participate in international and regional comparisons. The training is aimed at providing metrologists with the necessary knowledge to build up the experience that will ultimately enable them to participate in regional comparisons and later in international comparisons.
For more detail contact Mr. Benjamin Van der Merwe.
Implementation of the GUM Supplement 1 for Monte Carlo Based Uncertainty Estimation
Metrology as practised at national metrology institutes has as a crucial underpinning the need to carry out Uncertainty Quantification (UQ) in a manner that adequately captures the methodology of approach as well in the scientific validity in results as befitting its application as a modern scientific field of research. In furtherance of this objective the Guide to Uncertainty in Measurement (GUM) is commonly utilized as a practical tool in the calculation of experimental uncertainties under certain limiting conditions [see e.g. web link NMISA-08-0121.pdf ] however the validity of some uncertainty estimates obtained through the application of the sensitivity coefficient based approach adopted in earlier versions of GUM are in certain instances not well understood.
The publication of the Joint Committee for Guides in Metrology (JCGM) "GUM Supplement 1" that has been adopted by the BIPM addresses the inclusion of the application of Monte Carlo techniques to UQ as a more generalized and powerful technique that is not limited to any particular measure and model assumptions. At the Pressure & Vacuum Laboratory some initial research work has been performed that investigates and examines the validity of approach in the specific area of primary scale pressure standards as discussed in a recent paper "Comparison of the GUM and Monte Carlo Measurement Uncertainty Techniques with Application to Effective Area Determination in Pressure Standards"[web link ijmqe2010010.pdf ] in the International Journal of Metrology and Quality Engineering (www.metrology-journal.org). Consequently within the laboratory with regards to laboratory pressure & vacuum secondary working standards traceable to primary standards the laboratory is adopting more of the philosophies of the newest version of the GUM that incorporates Monte Carlo uncertainty estimation through better mathematical models implemented with Matlab (and its equivalent free open source alternative Gnu Octave) that complement and extend existing sensitivity coefficient based uncertainty results performed in traditional spread sheet based platforms such as MS Excel in those instances where such validity assumptions and approximations are inaccurate or flawed.