Showing papers in "Measurement Science and Technology in 1992"
TL;DR: In this article, a calibration procedure for the Anton Paar DMA 512 densimeter usable at pressures up to 40 MPa was presented. But the method is based on water as a reference substance and requires knowledge of the characteristics of the cell as functions of temperature when subjected to a vacuum lower than 100 Pa.
Abstract: This article reports a calibration procedure for the commercial Anton Paar DMA 512 densimeter usable at pressures up to 40 MPa. The method is based on water as a reference substance and requires knowledge of the characteristics of the cell as functions of temperature when subjected to a vacuum lower than 100 Pa. Comparis on with data from the literature indicates a relative accuracy of 0.1% where the classical calibration method (i.e. assuming no dependence of the densimeter performance upon pressure) led to a relative accuracy of 0.8% for the same substances.
220Â citations
TL;DR: The dielectrophoretic characteristics of normal, leukaemic, and differentiation-inducedLeukaemic mouse erythrocytes were measured as a function of frequency in the range 5*102-105 Hz and were shown to be significantly different.
Abstract: A method was developed for studying the dielectrophoretic properties of both homogeneous and mixed populations of mammalian cells. Computerized image analysis was employed to quantify the rate of motion of cells suspended in low conductivity medium as they moved under the influence of a non-uniform alternating electric field produced by an interdigitated electrode array. As expected for dielectrophoresis, cells collected at highly inhomogeneous electric field regions of the array when the electrical polarizability of cells exceeded that of the suspending medium or away from such regions when their polarizability was less than that of their medium. These two types of behaviour are classified as positive or negative dielectrophoresis respectively, and the cell collection patterns agreed well with those computed for the electrode configuration employed. The dielectrophoretic characteristics of normal, leukaemic, and differentiation-induced leukaemic mouse erythrocytes were measured as a function of frequency in the range 5*102-105 Hz and were shown to be significantly different.
192Â citations
TL;DR: In this paper, a high-field/high-frequency EPR and endor system operating at 3 mm wavelength is described, and the probe-head designs of two different resonator types, i.e., an open Fabry-Perot resonator and a cylindrical TE011 cavity, are presented in detail.
Abstract: A high-field/high-frequency EPR and ENDOR system operating at 3 mm wavelength is described. The probe-head designs of two different resonator types, i.e. an open Fabry-Perot resonator and a cylindrical TE011 cavity, are presented in detail. The advantages and limitations of high-field/high-frequency EPR and ENDOR spectroscopy are demonstrated for selected examples. The performance data of the spectrometer suggest that it will be very useful for broad applications in physics, chemistry and biology.
176Â citations
TL;DR: In this paper, the authors compare electrostatic and piezoelectric transducers and show that composite transducers consisting of piezoceramic and polymer materials show a wider relative bandwidth of about 30% at the expense of efficiency.
Abstract: Many measurement tasks in industrial automation, e.g. non-contact distance measurement, room surveillance, object identification and gas flow measurement can be accomplished by sensors using airborne ultrasound. Their performance is determined by the properties of the ultrasonic transducers. The authors compare electrostatic and piezoelectric transducers. Piezoceramic transducers combine a high efficiency factor and ruggedness. Composite transducers consisting of piezoceramic and polymer materials show a wider relative bandwidth of about 30% at the expense of efficiency. Ultrasonic transducers based on piezopolymer foils offer a variety of acoustic properties at low expenditure. Their bandwidth corresponds to that of composite transducers. Composite, as well as piezopolymer, foil transducers are suited to the design of phased arrays. Foil transducers have the additional advantage of very small crosstalk between neighbouring transducer elements. By electronically controlled deflection of the sound beam, lateral details and consequently the spatial structure of objects can also be detected.
168Â citations
TL;DR: In this paper, the authors present an overview of surface evaluation techniques that are appropriate for characterizing the surface roughness of optical thin films and surfaces, ranging from low power optical microscopes to scanning probe microscopes.
Abstract: The author presents an overview of evaluation techniques that are appropriate for characterizing the surface roughness of optical thin films and surfaces. These include microscopes ranging from low power optical microscopes to scanning probe microscopes that can measure the topography of individual atoms or groups of atoms, optical non-contact and mechanical contact profilers, some of which can give topographic maps of surface areas, and total integrated scattering and angle-resolved scattering that yield statistical properties of surfaces. Theories are needed to relate scattering to surface roughness; these are valid only for certain types of roughness. Examples are given showing how various surface evaluation techniques can be used for characterizing selected surfaces.
135Â citations
TL;DR: In this article, the phase difference between interferograms obtained from a phase shifting interferometer is calculated using Lissajous figures and ellipse fitting, and two phase extraction algorithms are presented.
Abstract: A novel method, utilizing Lissajous figures and ellipse fitting, of calculating the phase difference between interferograms obtained from a phase shifting interferometer is described. Intensity bias and intensity modulation of interferograms are also calculated using this technique. Two new phase extraction algorithms are presented which use intensity and phase step information to calculate a surface from interferograms acquired with uneven phase steps. One algorithm allows surface phase to be calculated from two interferograms. Preliminary results from the Lissajous figure technique and the presented algorithms are discussed.
134Â citations
TL;DR: In this paper, a new method for the design of gradient coil systems for magnetic resonance imaging (MRI) with minimum energy is presented, which can deal with the eddy currents induced in conducting objects, and with shielded or double-shielded coil systems.
Abstract: The author presents a new method for the design of gradient coil systems for magnetic resonance imaging (MRI) with minimum energy. The new method eliminates previous restrictions on coil geometry and provides a unified approach for systems of any shape, including traditional cylindrical and planar systems. Realistic constraints can easily be enforced, such as the length of the cylinder in a cylindrical system, the size of the plane in a planar system, or the presence of current-free slots or holes. The method can deal with the eddy currents induced in conducting objects, and with shielded or double-shielded coil systems. The magnetic energy is minimized after all effects have been included, resulting in a truly optimized real-world system. The method also employs a new optimization scheme. A design example is presented and shown to have a substantially lower energy, smaller inductance and better gradient quality than previous similar designs.
130Â citations
TL;DR: In this article, a versatile electron-ion coincidence spectrometer for photoionization studies is described, which consists of a 127 degrees cylindrical electrostatic energy analyser and a time-of-flight energy analyzer.
Abstract: A versatile electron-ion coincidence spectrometer for photoionization studies is described. The spectrometer incorporates a 127 degrees cylindrical electrostatic energy analyser and a time-of-flight energy analyser. The two analysers are mounted on a turntable that can be rotated with respect to the polarization axis of the photon beam. Both analysers have a penetrating field stage which provides very high detection efficiency over a large solid angle and excellent threshold energy resolution ( approximately 3 meV) for the detection of charged particles. The analysers can also detect energetic particles. The time-of-flight analyser is used specifically for the separation and detection of different charge states of molecular photodissociation products. The use of the spectrometer to observe photoelectron-photo-ion coincidences and photoelectron-photoelectron coincidences in a variety of experiments (TPEPICO, PEPICO, TPEPECO) is illustrated by a study of the photo-double ionization of argon and of the dissociation products from the v=0 level of the c state of oxygen at 24.56 eV. Additionally, a spectrum of coincidences between threshold photoelectrons (TPESCO) is presented in the region of the 3P double ionization potential of argon.
109Â citations
TL;DR: In this article, the authors described the manner in which medium-frequency ultrasonic pulses travelling through concrete are generated, received, digitized and analyzed by partitioning the signal into discrete windows in the time domain, corresponding to the emergence of individual wave phenomena within the medium.
Abstract: The manner in which medium-frequency ultrasonic pulses travelling through concrete are generated, received, digitized and analysed is described Due to the highly attenuating nature of this medium and its differential effects on the frequency composition of broad-band signals, signal analysis was performed by partitioning the signal into discrete windows in the time domain, corresponding to the emergence of individual wave phenomena within the medium These windows were then transformed to the frequency domain for subsequent filtering and interpretation Experimentation combined with theoretical modelling has shown that the appearance and decay of discrete frequency bands depends on both the composition of the concrete, termed the resonance phase, and its external importance with respect to the ultrasonic inspection of concrete and other such inhomogeneous materials
79Â citations
TL;DR: The signal-to-noise ratio (SNR) improvement given by the new design is equal to that of the matched filter for the signal under consideration, and hence is maximal when the noise is Gaussian and additive.
Abstract: A design is presented for a phase-sensitive detector (PSD) based on matched filter theory, which is implemented using digital signal processing (DSP). The signal-to-noise ratio (SNR) improvement given by the new design is equal to that of the matched filter for the signal under consideration, and hence is maximal when the noise is Gaussian and additive. The theory of operation of analogue phase-sensitive detectors is discussed, and the SNR improvement obtained by using an ideal PSD is derived, along with the specific conditions under which this SNR can be expected. The limitations of real PSDs are then discussed. The new design is then presented in detail and its performance is compared to the analogue PSD. Experimental results are given which support the theoretical model of the demodulator, and an example of the use of the demodulator in a real application is given.
70Â citations
TL;DR: In this article, an outline of the principles that should be followed in the design and operation of an equal-arm beam balance for very precise weighing is presented, with a detailed discussion on the mechanical aspects of the design, and precautions to be taken to achieve mechanical stability.
Abstract: An outline of the principles that should be followed in the design and operation of an equal-arm beam balance for very precise weighing is presented. A detailed discussion on the mechanical aspects of the design and on precautions to be taken to achieve mechanical stability is given. The effects of anelasticity in the pivots, ground vibrations and temperature changes are also described. Comparisons are drawn between the behaviour of knife edges and flexure strips as pivots and between their relative merits. Examples are given of some very precise weighings, reaching in one case a standard deviation of 4 parts in 1012. The factors that may ultimately limit the accuracy of weighing are indicated.
TL;DR: Two methods for performing tracking of particles in a fluid flow using a dynamic, binary, spatial, cross-correlation technique and a traditional PIV method are presented.
Abstract: The practical use of particle image velocimetry (PIV) requires the use of fast, reliable, computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple, sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images, uses a dynamic, binary, spatial, cross-correlation technique. The algorithms were tested on both synthetic data and experimental data which were obtained with traditional PIV methods. This allowed error analysis and testing of the algorithms on real engineering flows.
TL;DR: In this article, the design and construction of a small compact autocollimator based on the laser head of a compact disc player is described, which provides a cheap and simple means of measuring angles over a total angular range of 1200 mu rad (approximately 200 arcsec) with a resolution of better than + or 0.006 mu rad.
Abstract: The design and construction of a small compact autocollimator based on the laser head of a compact disc player is described. The instrument provides a cheap and simple means of measuring angles over a total angular range of 1200 mu rad ( approximately 200 arcsec) with a resolution of better than +or-0.006 mu rad. The 100 mu rad central region of the measurement range is linear to better than 2%. The autocollimator head is compact and can operate over long distances and with high ambient lighting. The unit described can, with a single measurement head, be used to simultaneously measure angles in two orthogonal directions.
TL;DR: In this article, a prototype of the fiber drop analyser (FDA) working at only one wavelength in the infrared has been constructed and tested and the instrument has been used to measure individually surface tension, viscosity, refractive index and the chemical composition of the test solution.
Abstract: An instrumental method for the individual, sequential or collective measurement of the physical and chemical properties of liquids is presented. A prototype of the fibre drop analyser (FDA), working at only one wavelength in the infrared, has been constructed and tested. The instrument has been used to measure individually surface tension, viscosity, refractive index and the chemical composition of the test solution. The instrument has the capability of simultaneously measuring all of these quantities in one measurement cycle and this possibility is discussed on the basis of one set of results obtained from the sugar processing industry. The instrument is also potentially capable of measuring electrochemical properties of a liquid and some preliminary results are presented. The laboratory FDA has been used to test a series of samples from a large cane sugar manufacturer's process and these measurements demonstrate that the FDA technology has the potential to be used as a remote optrode industrial process monitor for sucrose manufacture, and possibly in other industrial applications.
TL;DR: In this paper, the authors developed a fully automated dynamic calorimeter, which can measure the dynamic specific heat of a liquid or solid sample as a function of frequency over the range of six decades 0.01 Hz-10 kHz.
Abstract: The authors have developed a fully automated dynamic calorimeter, which can measure the dynamic specific heat of a liquid or solid sample as a function of frequency over the range of six decades 0.01 Hz-10 kHz. The shape of a solid sample can be either wire or planar. At low frequencies, the measured quantity corresponds to the usual static specific heat. With this probe, one can study the slow dynamics occurring in condensed matter systems.
TL;DR: In this paper, a two-colour interferometer for the compensation of the refractive index of air is described, which counts two types of interference fringes which are in phase quadrature by means of a lambda /8 plate.
Abstract: A high-accuracy length-measuring two-colour interferometer for the compensation of the refractive index of air is described. It counts two types of interference fringes which are in phase quadrature by means of a lambda /8 plate. The light source is a diode laser pumped YAG laser of about 40 mW output power; its second harmonic wave is generated by a KTiOPO4 (KTP) crystal. The resolution in determining the refractive index of air is improved by averaging the numbers of the interference fringes counted. The interferometer is evaluated to be better than 2*10-7 in accuracy.
TL;DR: In this paper, the performance of a family of mid-infrared monitors for measuring carbon dioxide and hydrocarbons is described and various schemes are outlined for compensating temperature drift, output/gain fluctuations, changes in cell transparency and mismatch between components.
Abstract: Infrared light emitting diodes (LEDS) can replace the thermal source, bandpass filters and rotating chopper wheel of conventional infrared gas monitors. Their long-term stability, high modulation rate and compact size also provide design advantages. The performance of a family of mid-infrared monitors for measuring carbon dioxide and hydrocarbons is described. Various schemes are outlined for compensating temperature drift, output/gain fluctuations, changes in cell transparency and mismatch between components.
TL;DR: In this paper, a DC SQUID magnetometer designed and constructed for high resolution magnetocardiographic measurements is presented, focusing in particular on the matching of the DC magnetometer with the gradiometer and the room temperature electronics.
Abstract: A ultra low noise DC SQUID magnetometer designed and constructed for high resolution magnetocardiographic measurements is presented. Details of the design considerations and the construction of the single-channel system are given, focusing in particular on the matching of the DC SQUID with the gradiometer and the room temperature electronics. Using a first-order gradiometer as antenna for biomagnetic fields, a white noise level of 2 fT Hz-1/2 has been attained with a 1/f corner frequency at 3 Hz. The intrinsic magnetic flux noise of the SQUID system of 2*10-6 Phi 0 Hz-1/2 corresponds to a noise limited sensitivity of 700 aT Hz-1/2.
TL;DR: In this article, the authors describe the operation of new thermopiles in the form of bimetallic printed circuits comprising numerous electrodes electroplated on a continuous foil of lower conductivity, and present new heat flow sensors which are directly responsive to the asymmetry of a fringing flow pattern induced by a normal heat flow to be measured.
Abstract: The authors describe the operation of new thermopiles in the form of bimetallic printed circuits comprising numerous electrodes electroplated on a continuous foil of lower conductivity. When a temperature gradient is applied in the direction parallel to the plane of lamination, such a device behaves like a thin-film thermoelectric element. In the more general case, where a heat flow tube is passed in the direction normal to the plane of lamination, the amount of EMF generated in the continuous support is determined by all the axial temperature gradients distributed in the double-layer thickness. As an application, the authors present new heat-flow sensors which are directly responsive to the asymmetry of a fringing flow pattern induced by a normal heat flow to be measured.
TL;DR: In this paper, simple signal processing tools are used to describe noise in sampled measurements, and particular attention is paid to aliasing and the modification of noise spectra by the sampling process.
Abstract: Simple signal processing tools are used to describe noise in sampled measurements. Particular attention is paid to aliasing and the modification of noise spectra by the sampling process. The principles discussed are applied to near-optimal measurements of DC and AC signals in noise, and to the measurement of noise power. Specific problems have been chosen to demonstrate novel approaches and to clarify situations where confusion has arisen. Examples include alternative definitions of equivalent noise bandwidth, the bandpass sampling theorem, quantization and dither, the variance in the mean of correlated measurements, the exploitation of anticorrelation in resonant transducers, the ideal averaging filter, the resolution of synchronous demodulators, and sampling demodulators.
TL;DR: The authors present the development of an electronic/digital technique which enables real-time shearographic fringes to be obtained and eliminates most of the shortcomings of the conventional technique.
Abstract: Shearography is an interferometric method which measures surface displacement derivatives. Although useful for strain analysis and non-destructive testing, the conventional technique is cumbersome and not very suitable for an industrial environment. The authors present the development of an electronic/digital technique which eliminates most of the shortcomings. It enables real-time shearographic fringes to be obtained.
TL;DR: In this paper, a turbulent flow reactor has been constructed for kinetic studies of homogeneous gas-phase hydrocarbon oxidation in the low to intermediate temperature regimes (T < 1000 K).
Abstract: A turbulent flow reactor has been constructed for kinetic studies of homogeneous gas-phase hydrocarbon oxidation in the low to intermediate temperature regimes (T<1000 K). A unique feature of the test facility is that its design provides the ability to study gas-phase kinetics while minimizing complications from transport effects and temperature gradients at pressures up to 20 atm. A novel experimental procedure designed to map the reactivity of hydrocarbon/air mixtures in the low to intermediate temperature regimes using carbon monoxide measurements as an indicator of the degree of oxidation has been developed.
TL;DR: In this paper, the authors describe a compact He beam apparatus developed for high resolution studies of surface structures by He diffraction and of surface vibrations by He energy-loss spectroscopy.
Abstract: The authors describe a compact He beam apparatus developed for high resolution studies of surface structures by He diffraction and of surface vibrations by He energy-loss spectroscopy. The angular resolution is 0.135 degrees FWHM (rotation of the sample) and the He beam intensity is 1019 atoms sr-1 s-1 at the sample. The apparatus is also equipped with Auger and ultraviolet photoemission spectroscopy. Measurements of He diffraction patterns and He energy loss spectra are reported from the (1*2) Au(110) surface and provide a full characterization of the apparatus.
TL;DR: The NPL standard humidity generator has been validated by assessment of the performance of individual components of the generator system as discussed by the authors and the results of these experiments have led to some improvements in the design of the standard.
Abstract: The NPL standard humidity generator-the reference for traceable humidity calibrations in the United Kingdom-has been validated by assessment of the performance of individual components of the generator system. The investigation has explored the effects of saturator efficiency, temperature conditioning of the gas, desorption, leaks, pressure variation and other factors that contribute to the uncertainty in dew-points generated by this instrument. The results of these experiments have led to some improvements in the design of the standard. Repeatability of overall performance has been monitored over a period of two years. The improvements in design, together with better characterization of the performance of the instrument, have enabled a smaller uncertainty in generated dew-point to be assigned. This uncertainty is now +or-0.05 degrees C dew-point in the middle of the operating range, rising to +or-0.08 degrees C and +or-0.15 degrees C dew-point at the upper and lower extremes of the range: +80 degrees C and -75 degrees C dew-point respectively.
TL;DR: In this article, a technique for the deposition of titanium dioxide coatings onto the end face of single-mode optical fibres by thermal and electron beam evaporation was described, and the absorption and reflectivities of the coatings were measured.
Abstract: Techniques are described for the deposition of titanium dioxide coatings onto the end face of single-mode optical fibres by thermal and electron beam evaporation. The absorption and reflectivities of the coatings were measured, and maximum reflectivities of 32% were achieved. Coated fibre ends were fusion spliced to similar, but uncoated, fibres using an electric arc. Optimum parameters for the arc were determined, thus yielding reflective splices having reflectivities of up to 25% and tensile strengths of 9 N. These reflective splices were used to form fibre optic Fabry-Perot interferometers yielding visibilities of up to 92%. Application of these reflective splices and interferometers as physical sensors is discussed.
TL;DR: In this paper, an instrument was developed to measure liquid-liquid interfacial tension based upon the drop volume method, which accurately measures the time elapsed for a known number of liquid droplets, formed under a constant flow rate, to detach from a submerged capillary orifice.
Abstract: An instrument has been developed to measure liquid-liquid interfacial tension based upon the drop volume method. The instrument accurately measures the time elapsed for a known number of liquid droplets, formed under a constant flow rate, to detach from a submerged capillary orifice. The size of the droplet is directly proportional to the liquid-liquid interfacial tension. The interfacial tension is calculated knowing the capillary orifice dimensions, liquid densities and drop volume. Droplet counting is automated with optical sensors, custom analogue and digital circuitry and a commercially available counter/timer. Constant flow is achieved through the use of a precision syringe pump. The importance of the capillary tip geometry on the measured interfacial tension has been established.
TL;DR: In this paper, a secondary emission detector for neutral particles has been constructed for an experiment to investigate the photodetachment process X-+h nu to X+e- where X- can be any negative ion.
Abstract: A secondary emission detector for neutral particles has been constructed. The detector is designed for an experiment to investigate the photodetachment process X-+h nu to X+e- where X- can be any negative ion. A beam of negatively charged ions is merged with a laser beam, and the rate of the photodetachment process is measured by monitoring the neutral atom production. The neutral atoms impinge on a coated glass plate where secondary electrons are formed which are detected with a channel electron multiplier. The laser beam strikes the glass plate at the same point as the neutral atoms do and the intense laser light produces electrons by the photoelectric effect. This gives rise to an unwanted signal which is much stronger than the desired signal induced by the neutral atoms. The neutral particle detector described is capable of preventing the detection of electrons produced by the photoelectric effect. It is shown that the detection of electrons produced by the light from pulsed lasers with pulse energies of up to 10 mJ and wavelengths down to 250 nm can be completely prevented without any decrease in the yield of the electrons produced by the neutral atoms. The detection efficiency of neutral atoms with an energy of 3 keV is shown to be 40%.
TL;DR: A series of different control strategies have been developed to improve the performance of an anthropomorphic prosthesis by detecting when the object slips and their combination improves the system's total performance by removing the false detection of slides whilst increasing sensitivity.
Abstract: Feedback signals from a transducer in an artificial hand or robot gripper are essential for the successful manipulation of objects. A series of different control strategies have been developed to improve the performance of an anthropomorphic prosthesis by detecting when the object slips. The methods are designed to be independent and so their combination improves the system's total performance by removing the false detection of slides whilst increasing sensitivity. The principal method of transduction uses a novel combined touch and slip sensor to detect the contact force as well as the vibrations set up when the object slips within the hand's grasp. Static and dynamic characteristics of the sensor are described. While the target application for this method is prosthetics, similar techniques can be applied to more general classes of robotic manipulation. These methods would improve a robot's response because the device does not require detailed recognition of a target object or its orientation prior to handling.
TL;DR: In this article, a model for an electrostatic ultrasonic transducer with a uniformly grooved backplate was constructed, and the membrane and the groove pattern of the transducers were divided into individual elements, and each element was treated as a Helmholtz resonator.
Abstract: A model has been constructed for an electrostatic ultrasonic transducer with a uniformly grooved backplate. The membrane and the groove pattern of the transducer was divided into individual elements, and each element was treated as a Helmholtz resonator. The resonant frequency of the transducer can be calculated using one single resonator element. The calculated resonant frequencies were compared with experimental results.
TL;DR: In this article, the authors measured the whole field temperature distribution of a laminar, axisymmetric, propane-air, fuel-lean flame using an advanced digital interferometric technique, namely digital phase-shifting holographic interferometry.
Abstract: Instead of using conventional interferometry, the whole field temperature distribution of a laminar, axisymmetric, propane-air, fuel-lean flame is measured by using an advanced digital interferometric technique, namely digital phase-shifting holographic interferometry. The measurement technique effectively improves the accuracy of conventional interferometric measurement as it circumvents the limitation of fringe counting interpolation. The results obtained by this technique are compared with those measured by conventional holographic interferometry (using interpolation) in order to evaluate the effect of interpolation on measurement accuracy. A modified dual reference beam holographic recording system is set up for this experiment and fast Fourier transformation is used for Abel inversion. The structure of the test flame is analysed by holographic visualization and measured temperature distribution. In addition, the interferometric temperature distributions are compared with thermocouple measurements. Errors introduced in the measurement are analysed and discussed.