Experimental investigation of low-voltage spark ignition caused by separating electrodes

Electric arcs pose an ignition hazard in the presence of flammable gas mixtures. Electrical equipment to be used in such hazardous environments shall therefore satisfy strict safety requirements, through the use of internationally standardized explosion protection methods as e.g. "Intrinsic Safety", documented in the IEC 60079-11 Standard.This "Intrinsic Safety" is verified by using a stochastic empirical procedure, using a "Spark Test Apparatus" connected to an electrical energy source. The apparatus generates electrical discharges between a separating tungsten anode and a cadmium cathode enclosed in a test cell filled with flammable gas atmosphere. The connected electrical circuit is considered intrinsically safe if no ignition results within a defined number of contacts. However this procedure suffers from variability and poor reproducibility.The goal of this work is to investigate the relationships between such arc discharges and the ignition of the gas. The measurement is technically challenging, as the physical processes occur in different time scales (ns, μs, ms) and the physical dimensions are small (μm). Additionally the ignition process can also damage the experimental equipment.An important prerequisite for such discharges is a sufficient degree of electrode surface wear. Microscope images show such electrode surfaces as well as the presence of metal whiskers. These inhomogeneous rough surfaces are compared by the means of Abbott curves.A spectral analysis of the radiation from the electrical discharge shows, that the main substance is cadmium vapour.The electrical characteristics of these arcs are characterised by voltage, current and length curves. For constant currents from 74 to 270 mA up to a voltage of 40 V, the transient arc lengths, voltages and currents were measured for arc discharges generated in a 21% Hydrogen-Air gas mixture. These initial results appear to correspond qualitatively to published curves for static arcs, however the accuracy of the measurements has to be improved.Knowledge of these relationships between electrical, mechanical and ignition processes will ultimately make it possible to recognize discharges which most likely cause an ignition by their current and voltage waveforms. This will allow the development of a more reliable alternative, where discharges are electronically simulated

Fast and accurate: high-speed metrological large range AFM for surface and nanometrology

Low measurement speed remains as a major shortcoming of the scanning probe microscopic techniques. It leads not only to a low measurement throughput, but also to a significant measurement drift over the long measurement time needed (up to hours or even days). In this paper, development of a high speed metrological large range atomic force microscope (HS Met. LR-AFM) with a capable measurement speed up to 1 mm/s is presented. In its design, a high accurate nanopositioning and nanomeasuring machine (NMM) is combined with a high dynamic flexure hinge piezo stage to move sample. The AFM output signal is combined with the position readouts of the piezo stage and the NMM to derive the surface topography. This design has a remarkable advantage that it well combines different bandwidth and amplitude of different stages/sensors, which is required for high speed measurements. While the HS Met. LR-AFM significantly reduces the measurement time while maintains (or even improves) the metrological performance than the previous Met. LR-AFM, its application capabilities are extended significantly. Two application examples, the realisation of reference areal surface metrology and the calibration of a kind 3D nano standards, have been demonstrated in the paper in detail

Co-Nanomet: Co-ordination of Nanometrology in Europe

Nanometrology is a subfield of metrology, concerned with the science of measurement at the nanoscale level. Today’s global economy depends on reliable measurements and tests, which are trusted and accepted internationally. It must provide the ability to measure in three dimensions with atomic resolution over large areas. For industrial application this must also be achieved at a suitable speed/throughput. Measurements in the nanometre range should be traceable back to internationally accepted units of measurement (e.g. of length, angle, quantity of matter, and force). This requires common, validated measurement methods, calibrated scientific instrumentation as well as qualified reference samples. In some areas, even a common vocabulary needs to be defined. A traceability chain for the required measurements in the nm range has been established in only a few special cases. A common strategy for European nanometrology has been defined, as captured herein, such that future nanometrology development in Europe may build out from our many current strengths. In this way, European nanotechnology will be supported to reach its full and most exciting potential. As a strategic guidance, this document contains a vision for European nanometrology 2020; future goals and research needs, building out from an evaluation of the status of science and technology in 2010. It incorporates concepts for the acceleration of European nanometrology, in support of the effective commercial exploitation of emerging nanotechnologies. The field of nanotechnology covers a breadth of disciplines, each of which has specific and varying metrological needs. To this end, a set of four core technology fields or priority themes (Engineered Nanoparticles, Nanobiotechnology, Thin Films and Structured Surfaces and Modelling & Simulation) are the focus of this review. Each represents an area within which rapid scientific development during the last decade has seen corresponding growth in or towards commercial exploitation routes. This document was compiled under the European Commission Framework Programme 7 project, Co-Nanomet. It has drawn together input from industry, research institutes, (national) metrology institutes, regulatory and standardisation bodies across Europe. Through the common work of the partners and all those interested parties who have contributed, it represents a significant collaborative European effort in this important field. In the next decade, nanotechnology can be expected to approach maturity, as a major enabling technological discipline with widespread application. This document provides a guide to the many bodies across Europe in their activities or responsibilities in the field of nanotechnology and related measurement requirements. It will support the commercial exploitation of nanotechnology, as it transitions through this next exciting decade

A novel pitch evaluation of one-dimensional gratings based on a cross-correlation filter

If one-dimensional (1D), p–period and arbitrarily structured grating position-related topographical signals coexist with noise, it is difficult to evaluate the pitch practically using the centre-of-gravity (CG) method. The Fourier-transform-based (FT) method is the most precise to evaluate pitches; nevertheless it cannot give the uniformity of pitches. If a cross correlation filter ̶ a half period of sinusoidal waveform sequence (pT period), cross-correlates with the signals, the noise can be eliminated if pT is equal to p. After cross-correlation filtering, the distance between any two adjacent waveform peaks along the direction perpendicular to 1D grating lines is one pitch value. The pitch evaluation based on the cross-correlation filtering together with the detection of peaks position is described as the peak detection (PD) method in this paper. The pitch average and uniformity can be calculated by using the PD method. The computer simulation has indicated that the average of pitch deviations from the true pitch and the pitch variations are less than 0.2% and 0.2% for the sinusoidal and rectangular waveform signals with up to 50% uniform white noise, less than 0.1% and 1% for the sinusoidal and rectangular waveform signals and 0.6% and 2.5% for the triangular waveform signal if three waveform signals are mixed with Gaussian white, binomial and Bernoulli noise up to 50 % in standard deviation, one probability and trial probability respectively. As the examples, a highly oriented pyrolytic graphite (HOPG) with 0.246 nm distance between atoms and a 1D grating with 3000 nm nominal pitch are measured by a ultra-high vacuum scanning tunneling microscope (UHV STM) and a metrological atomic force microscope (AFM) respectively. After the position-related topographical signals are cross-correlation filtered, the 0.240 nm and 3004.11 nm pitches calculated by using the PD method are very close to the 0.240 nm and 3003.34 nm results evaluated by the FT method

A novel pitch evaluation method based on a cross-correlation filter

A cross correlation filter ̶ a half period of sinusoidal waveform sequence (pT period), is applied to filter the topographical signal (p period )of 1D arbitrary-form grating against positions. It, as a template, cross-correlate with the signal and the noise that coexists with signal is eliminated if pT p. After filtering, the distance between any two adjacent waveform peaks along the direction perpendicular to 1D grating lines is one pitch value, the peak-detection (PD) method. In this method, the pitch average and uniformity can be calculate

Atomic force microscope cantilevers as encoder for real-time displacement measurements

We have investigated the use of atomic force microscope (AFM) cantilevers as encoder for real-time high-resolution displacement measurements. Mathematical derivations show that two AFM cantilevers signals are needed for real-time forward and backward displacement measurements in any planar direction and in x- or y-axis direction respectively when two are paired with a 1D sinusoidal grating. Tuning-fork (TF) cantilevers are the best choice among AFM cantilevers for the setup of a multi-cantilever encoder head. During the study an AFM head with up to three TF cantilevers as the encoder has been designed and built. The system was experimentally tested for its performance and feasibility of real-time displacement measurements in x- or y- axis by using two cantilevers. To achieve a correct reading the distance between two cantilever tips is preset in such a way that the two 1D sinusoidal grating position-encoded signals have a quadrature phase shift form. The decoding algorithm is based on directly unwrapping of the phase from the signals in real-time. Cross-correlation filtering and differentiation process of two encoded signals could be applied to suppress the noise and to reduce the offset and tilt of the encoded signals and by this allows a successful implementation of real-time displacement measurements

Real-time cross-correlation filtering of a one-dimensional grating position-encoded signal

A cross-correlation technique is adopted and applied to the real-time signal filtering of a one-dimensional (1D) grating position-encoded signal scanned by a micro- or nano-probe. The position-encoded signal is used for both real-time displacement measurement and grating pitch measurement. The filtering technique applied is based on the 1D grating position-encoded signal which is passed over by a half period of sinusoidal waveform sequence as the template and is cross-correlated with it. Mathematical analysis and simulation experiment are performed not only to optimize the parameters of the template but also to prove the accuracy and credibility of real-time filtering when the template period is approximately equal to that of the 1D grating position-encoded signal. As an application, the motion displacements of a piezoelectric scanning stage are measured when it is controlled to move by a computer through its built-in capacitance sensor in open- and closed-loop modes respectively at different moving speeds

Measurements of dimensional standards and etalons with feature size from tens of micrometres to millimetres by using sensor strengthened nanomeasuring machine

A laser focus sensor and a contact inductive sensor have been coupled to an ultra high precision positioning stage, referred to as a nanomeasuring machine (NMM), for measurements of dimensional standards with a large measurement volume of 25 mm x 25 mm x 5 mm. Control and measurement software have been designed and complemented. The measurement uncertainty of strengthened NMM has been analyzed and discussed. Groove depth and step height standards with feature heights of tens of micrometres to millimetres as well as aspherical surface etalons are calibrated by nanomeasuring machine. The paper also introduces a method for characterising the measured aspheric surface by least square fitting the measured data to a quadratic paraboloid function. The obtained quadratic coefficients are compared to that measured by a conventional coordinate measuring machine (CMM) and a stylus profiler, showing a good agreement

Influence of Geometric Properties of Capacitive Sensors on Slope Error and Nonlinearity of Displacement Measurements

Capacitive sensors are widely used in industrial applications, such as CNC machine tools, where reliable positioning in the micrometer range with nanometer accuracy is required. Hence, these sensors are operated in harsh industrial environments. The accuracy of these sensors is mainly limited by slope errors and nonlinearities. In practice, the required accuracy of these sensors is achieved by a calibration against a metrological high-quality reference such as interferometric displacement measurement systems. This usually involves the use of high-order polynomials as calibration functions based on empirical data. In metrology, this is only the second-best approach and has disadvantages in terms of stability over the measurement range of the instrument. In addition, the validity of these empirical calibrations over time is questionable, and the associated uncertainty can only be roughly estimated. This makes regular recalibration of such sensors at short intervals mandatory to ensure the reliability of the displacement measurement. In this paper, we report on our investigations of the different parameters that affect the accuracy of capacitive sensors. Since the capacitance of these sensors results from the electric fields that build up between the electrodes, these field lines are calculated using FEM simulation models for typical commercial sensors. In the following the influence of various geometric parameters such as edge radius, guard ring size and shape, or thickness of the electrodes are individually analyzed according to their impact on the accuracy of these sensors. Based on these simulations, the deviations of the capacitance as they arise for real detector geometries can then be compared with idealized, de facto unrealizable parallel plate capacitors. This methodology allows overall uncertainty of capacitive sensors to be decomposed into their individual components and sorted in terms of their contribution to the uncertainty budget. The individual FEM-based analysis then enables a systematic analysis of the sources of uncertainty and, thus, reveals possibilities to improve manufacturing processes for capacitive sensors, to put these sensors on a solid metrological basis, and to improve the performance of these displacement measurement systems in the long run, i.e., to provide better sensors for the application

Tuning-Fork Atomic Force Microscope Cantilever Encoder and Applications for Displacement and In-Plane Rotation Angle Measurement

One tuning-fork cantilever integrated in a home-built atomic force microscope (AFM) has been investigated to be used as an encoder for real-time forward or backward displacement measurement when paired with 1D grating. The decoding principle is based on direct count of integer periods plus calculation of two fractional parts in encoded signal at the beginning and at the actual position corresponding to a segment of displacement. Cross-correlation technique has been employed to filter 1D grating encoded signal in real time. The encoder has been used to measure forwards or backwards displacement and to monitor the scanning stage, during motion, to control its displacement. It can also be used for the measurement of in-plane rotation angle between1D grating orientation and micro moving stage within 90° range. The criteria for the angle measurement are explained and the measurement data are shown