Showing papers in "Measurement Science and Technology in 1993"
IBM1
TL;DR: In this article, the state of the art in high-resolution displacement measuring interferometry is reviewed, and several approaches to improve this situation are described, including multi-wavelength inter-ferometry.
Abstract: The present state of high-resolution displacement measuring interferometry is reviewed. Factors which determine the accuracy, linearity and repeatability of nanometre-scale measurements are emphasized. Many aspects of interferometry are discussed, including general metrology and alignment errors, as well as path length errors. Optical mixing and the nonlinear relation between phase and displacement are considered, as well as the influence of diffraction on accuracy. Environmental stability is a major factor in the repeatability and accuracy of measurement. It is difficult to obtain a measurement accuracy of 10-7 when working in air. Several approaches to improving this situation are described, including multiwavelength interferometry. Recent measurements of the short- and long-term frequency stability of lasers are summarized. Optical feedback is a subtle, but important source of frequency destabilization, and methods of detection and isolation are reviewed. Calibration of phase measuring electronics used for subfringe interpolation is included. Progress in 'in situ' identification of error sources and methods of validating accuracy are emphasized.
496 citations
TL;DR: An introduction to the tin dioxide (SnO2) ceramic gas sensor and its electrical characterization is presented, followed by details of some methods of active material preparation and problems of sensitivity, selectivity and their modification are then considered as discussed by the authors.
Abstract: An introduction to the tin dioxide (SnO2) ceramic gas sensor and its electrical characterization is presented, followed by details of some methods of active material preparation. Problems of sensitivity, selectivity and their modification are then considered. The basic measurand is the conductance of the sensor, which means that the active material must always bridge a pair of electrodes; it must also be heated to several hundred degrees Celsius above ambient for successful operation. Descriptions of basic design approaches to the relevant electronic circuits are presented.
214 citations
TL;DR: A statistical method for automatic quality control of measurement data with distributions close to Gaussian is presented and, using the best one of these, the method is tested using artificial and real turbulence data.
Abstract: A statistical method for automatic quality control of measurement data with distributions close to Gaussian is presented. For each data point a prediction is made, based on the mean, variance and point-to-point correlation of the time series. The predicted value is compared with the actual value and if the difference between the two is 'large' then that data point is either marked as an outlier or replaced by the forecast value. Four different prediction methods are tested and, using the best one of these, the method is tested using artificial and real turbulence data.
164 citations
TL;DR: The theory of measurement uncertainty outlined in this article forms the mathematical foundation of the results of international discussions of many years and is universally applicable to most measurement data evaluation tasks including complex nonlinear adjustments and, in particular, in cases where the well-established least-squares or maximum-likelihood techniques fail, as in strongly underdetermined few-channel particle energy spectrum unfolding problems.
Abstract: The theory of measurement uncertainty outlined forms the mathematical foundation of the results of international discussions of many years. In contrast to the usual approaches in the literature, it is based entirely on Bayesian statistics and on the principle of maximum entropy. Individual and mutual uncertainties of measurement results are expressed and treated by a covariance matrix in conformity with international recommendations. The theory is universally applicable to most measurement data evaluation tasks including complex nonlinear adjustments and, in particular, in cases where the well-established least-squares or maximum-likelihood techniques fail, as in strongly underdetermined few-channel particle energy spectrum unfolding problems.
157 citations
TL;DR: An electronic nose is described, which consists of a gas sensor array combined with a pattern recognition routine, and it is shown how a net based on unsupervised training could be used to predict storage time for ground beef.
Abstract: An electronic nose is described, which consists of a gas sensor array combined with a pattern recognition routine. The sensor array used consists of ten metal-oxide-semiconductor field effect transistors with gates of catalytically active metals. It also contains four commercially available chemical sensors based on tin dioxide, so-called Taguchi sensors. In some studies, a carbon dioxide monitor based on infrared absorption is also used. Samples of ground beef and pork, stored in a refrigerator, have been studied. Gas samples from the meat were then led to the sensor array, and the resulting patterns of sensor signals were treated with pattern recognition software based on an artificial neural network as well as with an algorithm based on an abductory induction mechanism. When using all sensors for learning, the two nets could predict both type of meat and storage time quite well. Omitting the carbon dioxide monitor, both nets could predict type of meat, but storage time not so well. Finally, it is also shown how a net based on unsupervised training could be used to predict storage time for ground beef.
154 citations
TL;DR: A microstrip quarter wavelength ( lambda g/4) resonator in conjunction with a small probe is used to resolve objects with characteristic dimensions as small as a thousandth of the wavelength as discussed by the authors.
Abstract: A microstrip quarter wavelength ( lambda g/4) resonator in conjunction with a small probe is used to resolve objects with characteristic dimensions as small as a thousandth of the wavelength ( lambda g/1000). The characteristic length for the decay of the evanescent waves at the tip of the probe was measured to be approximately 100-150 mu m at a microwave frequency of 1 GHz ( lambda free approximately=30 cm). The authors applied this technique to map microwave conductivity of metallic lines on glass and printed circuit boards and to investigate conductivity variations across a silicon wafer. It was possible to detect holes in printed circuit boards that were covered with solder and were not detectable otherwise.
138 citations
TL;DR: In this article, a high sensitivity thermoluminescence (TL) spectrometer capable of producing 3D isometric plots of TL intensity against wavelength and temperature is described.
Abstract: A high sensitivity thermoluminescence (TL) spectrometer capable of producing 3D isometric plots of TL intensity against wavelength and temperature is described. The use of multichannel detectors (imaging photomultiplier tubes) with matched gratings gives optimum detection efficiency for TL signals over a wide spectral range (200-800 nm), and at heating rates normally used for standard TL applications. Spectra have been recorded from dosimeter phosphors and minerals at low dose levels; several examples are given.
135 citations
TL;DR: The linearly increasing stress test (list) as discussed by the authors is a load-controlled version of the CERT test, with the essential difference that the list test is load controlled whereas the Cert test is displacement-controlled.
Abstract: This paper presents a new testing apparatus for stress corrosion research. In this linearly increasing stress test (LIST) method, plain un-notched specimens are simultaneously exposed to an environment and subjected to an applied stress increasing linearly at a controlled rate. Experiments are repeated at various applied stress rates and the parameters measured include SCC initiation stress (the stress at which stress corrosion cracks start to propagate), fracture stress and average crack velocity. The LIST test is similar to the constant extension rate test (CERT) test, with the essential difference that the LIST test is load-controlled whereas the CERT test is displacement-controlled. The LIST test is particularly aimed at service conditions of loaded parts and structures; that is, service conditions described as load-controlled. This paper describes the design, construction and operation of the test apparatus and some typical results are given to illustrate its performance. Experiments have been conducted using as-quenched 3.5Ni-Cr-Mo-V turbine rotor steel specimens in aerated distilled water at 90 degrees C at stress rates varying from 0.00034 MPa s-1 to 2.08 MPa s-1.
99 citations
TL;DR: In this article, a third-order correlation system has been developed, which enables the contrast ratio of high-intensity ultra-short laser pulses to be measured on a single shot with a dynamic range of better than 108.
Abstract: A third-order correlation system has been developed, which enables the contrast ratio of high-intensity ultra-short laser pulses to be measured on a single shot, with a dynamic range of better than 108.
82 citations
TL;DR: All regimes tested in this work have been successfully reconstructed with the new algorithm, and the reconstructions are compared with images produced by the well-known linear back projection algorithm.
Abstract: In this work a new reconstruction algorithm for use with oil/gas pipe flow imaging has been developed. Accurate images of representative oil/gas distributions (that is, flow regimes) occurring in flow pipes has been obtained. A capacitance sensor system has been used. In the algorithm the oil/gas distribution has been represented by a set of parameters describing the oil/gas interface. A finite-element-based mathematical simulator of the multi-electrode capacitance sensor system has been developed. The simulator is capable of calculating the capacitances for a set of input parameters (namely for a given oil/gas distribution). The reconstruction algorithm calculates the image by finding the parameters that give fewest discrepancies between calculated and measured capacitances, using an optimization routine. All regimes tested in this work have been successfully reconstructed with the new algorithm, and the reconstructions are compared with images produced by the well-known linear back projection algorithm. The new algorithm has been tested using data from a capacitance imaging system; however, it can in principle be used with other imaging techniques.
69 citations
TL;DR: In this article, the electrical conductivity and capacitive reactance of milk and cream samples, of fat content ranging from 0.15 to 51% w/w, were reported over the frequency range 5 Hz to 200 kHz.
Abstract: The electrical conductivity and capacitive reactance of milk and cream samples, of fat content ranging from 0.15 to 51% w/w, are reported over the frequency range 5 Hz to 200 kHz. Measurements made at 100 kHz, where electrode polarization effects are negligible, indicate that the conductivity of milk and cream increases as a near 1.7 power law of the fat-free weight fraction present. With careful temperature control and the use of a reference skimmed milk sample to correct for variations in non-fat solids and ionic composition between batch samples, for skimmed milk (0.15% w/w fat) the fat content can be determined to within +or-0.08% w/w, whilst for double cream (51% w/w fat) the maximum uncertainty is 0.8% w/w fat. Previous work in the literature has been restricted to a smaller range of fat contents, using measurements where the influence of electrode polarization effects could not be completely eliminated.
TL;DR: A Tian-Calvet heat-flux microcalorimeter system for measurement of adsorption and reaction on solid surfaces has been described in this paper, where the transducers surround quartz calorimeter cells connected to a high-vacuum, volumetric adaption system.
Abstract: A Tian-Calvet heat-flux microcalorimeter system is described for measurement of heats of adsorption and reaction on solid surfaces. Heat-flux signals are measured in transducer assemblies consisting of several hundred Seebeck-effect thermoelements connected in series and arranged in a thimble configuration. These transducers surround quartz calorimeter cells connected to a high-vacuum, volumetric adsorption system. The sensitivity of the calorimeter can be calibrated with a Joule-effect device or by measurement of heats of adsorption for known processes. Microcalorimetric measurements have been conducted at temperatures from 300 to 473 K, and operation at temperatures from about 200 to 573 K is possible. Calorimeter cells are described that facilitate sample handling under controlled atmosphere conditions, allowing studies of freshly treated materials and samples that have been exposed to catalytic reaction conditions.
TL;DR: In this article, the authors present an instrument employing an auto-balancing technique via a negative feedback that zeros the static value and the very slow fluctuations of both the transducers and the stray capacitances, allowing high signal amplification and thus high sensitivity.
Abstract: Capacitance transducers are used in different applications such as measurement of vibrations, displacement, pressure, fluid density and so on. Depending on the application, transducers can have both floating electrodes, or in some cases, one earthed. Shielding techniques introduce parasitic capacitances, the compensation of which requires methods ranging from measuring configurations for floating capacitances up to more complicated techniques when one of the two transducer electrodes is earthed. The authors present an instrument employing an auto-balancing technique via a negative feedback that zeroes the static value and the very slow fluctuations of both the transducer and the stray capacitances, allowing high signal amplification and thus high sensitivity. The measuring circuit is composed essentially of a phase-sensitive detector and an integrating feedback path. A sensitivity of 1 mV fF-1 and a measurement range up to 10 pF is obtained, while an equivalent capacitance noise of 0.5 fF has been measured in the presence of a three-decade bandwidth.
TL;DR: A high-speed, high-resolution, digital computer-based interrogation system for particle image velocimetry (PIV) has been developed that utilizes advanced parallel array processing technology to achieve computational speeds comparable to those of current supercomputers.
Abstract: A high-speed, high-resolution, digital computer-based interrogation system for particle image velocimetry (PIV) has been developed. It utilizes advanced parallel array processing technology to achieve computational speeds comparable to those of current supercomputers, and high-resolution image acquisition equipment to achieve the data input rates necessary for high-speed analysis of PIV images. Advanced cross correlation techniques are incorporated into the algorithm, which take advantage of the high-speed capabilities and improve the quality of the measurements. The architecture, algorithms, and performance characteristics of the system are described.
TL;DR: In this article, a method is described that allows the ultrasonic absorption coefficient alpha of liquids to be precisely measured between about 1 and 100 MHz, which is achieved by careful construction and adjustment of the specimen cell, by semi empirical consideration of diffraction effects within the sample, and by precise calibration of the set-up by a specially designed below cut-off piston attenuator.
Abstract: A method is described that allows the ultrasonic absorption coefficient alpha of liquids to be precisely measured between about 1 and 100 MHz. The automatic measuring procedure can be performed easily and comparatively fast. At high alpha values the accuracy of the method is clearly superior to the more time-consuming resonator technique, which is applied in this frequency range. This accuracy is achieved by careful construction and adjustment of the specimen cell, by semi empirical consideration of diffraction effects within the sample, and by precise calibration of the set-up by a specially designed below cut-off piston attenuator. The short measuring time is enabled by the particular mode of operation also described in this paper.
TL;DR: In this article, it was shown that rotating the two orthogonal linearly polarized inputs of a heterodyne interferometer relative to the polarizing beam splitter axes produces second harmonic errors in an ideal interferometry.
Abstract: We show, using a Jones matrix analysis, that rotating the two orthogonal linearly polarized inputs of a heterodyne interferometer relative to the polarizing beam splitter axes, produces second harmonic errors in an otherwise ideal interferometer. The error undergoes two cycles as the optical pathlength difference changes from 0 to 2pi. This behaviour is distinct from previously reported periodic errors resulting from polarization leakage and frequency mixing. It is found that as the angular misalignment increases, the amplitude of the periodic errors also increases, and may reach substantial values.
TL;DR: In this article, an active compensation technique for improving the performance of a mu-metal magnetically shielded room is presented, which is based on measuring the magnetic field inside the room by a SQUID magnetometer.
Abstract: New results on an active compensation technique for improving the performance of a mu -metal magnetically shielded room are presented. This technique is based on measuring the magnetic field inside the room by a SQUID magnetometer. The output of this sensor is used to feed a current through a coil surrounding the room, thus compensating the field detected inside the room. After previous experiments on a single walled room, we applied the technique to a room with two mu -metal walls. At low frequencies a shielding improvement of more than 40 dB was obtained. Furthermore, the contribution of the intrinsic noise of the compensation electronics to the noise present in the room was considered. Also the possibility of using a normal conducting coil outside the room as the sensor in the compensation loop was tested. In the paper, the compensation set-ups are described and experiments are presented and discussed.
TL;DR: In this paper, the spatial profiles of molecular beams formed by both single and multicapillary sources have been investigated for He, Ne, Ar, Kr, H2 and N2, at distances from the source exit and driving pressures typical of those used in atomic collision experiments (1-5 mm and 0.02-10 Torr respectively).
Abstract: The spatial profiles of molecular beams formed by both single and multicapillary sources have been investigated for He, Ne, Ar, Kr, H2 and N2. The profile measurements were undertaken at distances from the source exit and driving pressures which are typical of those used in atomic collision experiments (1-5 mm and 0.02-10 Torr respectively). The experimental results indicate the clear superiority of a capillary array source over a single tube source, of similar overall dimensions, in producing a well collimated molecular beam over a wide range of driving pressures and distances from the capillary exit. They also indicate that there is a measurable dependence of the beam profile on gas species, particularly at the higher pressures studied. The significance of this result for the relative flow, cross section normalization technique is discussed.
TL;DR: In this paper, a novel optical fiber sensor has been developed for on-line monitoring of oil quality within industrial equipment, which is based on chromatic modulation because of the inherent self-referencing demonstrated by this technique.
Abstract: A novel optical fibre sensor has been developed for on-line monitoring of oil quality within industrial equipment. The monitoring is based on chromatic modulation because of the inherent self-referencing demonstrated by this technique. The sensor is shown to exhibit long-term stability and is capable of operating up to a temperature of 120 degrees C. Several industrial oils have been examined using the sensor, and typical modulation depths of 20% were obtained with resolution in the range of 0.1%. This is sufficient to record some interesting physical and chemical changes related to the reaction kinetics of oil degradation. The sensor is also capable of detecting oil leaks within a system since it can distinguish between the chromaticities of oil and air.
TL;DR: In this article, second-order space focusing in two-field time-of-flight mass spectrometers is studied and the design equations for second order space focusing are given.
Abstract: Design equations are given for second-order space focusing in two-field time-of-flight mass spectrometers. Simulations and experimental tests confirm that, for diffuse sources and high-energy fragments, second-order designs give superior resolution and linearity of flight time deviations to initial ion velocities.
TL;DR: In this article, a fiber optic force microscope scan head is used to scan the cantilever relative to a fixed sample, which enables the fibre-to-cantilever distance to be altered by moving the fibre relative to the fixed cantilevers.
Abstract: The authors have built a fibre optic force microscope scan head which scans the cantilever relative to a fixed sample. The design enables the fibre-to-cantilever distance to be altered by moving the fibre relative to the fixed cantilever. This design feature is particularly important when using the variable deflection mode and for acquiring force versus distance curves. The interferometer system reaches a resolution of 0.01 nm (peak-to-peak).
TL;DR: In this paper, the design of a single-beam gamma densitometer operated in the count mode is briefly described, which is suitable for two-phase flow void fraction measurement in small diameter tubes.
Abstract: The design of a single-beam gamma densitometer operated in the count mode is briefly described. The design is simple and reasonably compact and is suitable for two-phase flow void fraction measurement in small diameter tubes. The influence of the various parameters and test conditions on the gamma densitometer has also been thoroughly examined. The void fraction results were calibrated against the readings from a set of quick-closing valves. The test results show that the performance of the gamma densitometer is good, and that the measurement algebraic error is within +or-5% (the rms deviation is less than 7%). It also shows that a good average void fraction could be obtained by measuring the volumetric void fraction for the small pipe size. The typical design of such a gamma densitometer is summarized.
TL;DR: In this article, an interferometric method for the investigation of phase objects which employs a Mach-Zehnder arrangement with objects being located outside is presented, which functions as a differential interferometer with the practical advantage that the sensitivity and the carrier fringe system can be chosen arbitrarily and independently.
Abstract: The authors present an interferometric method for the investigation of phase objects which employs a Mach-Zehnder arrangement with objects being located outside. It functions as a differential interferometer with the practical advantage that the sensitivity and the carrier fringe system can be chosen arbitrarily and independently. The computerized evaluation is well adapted to the experimental set-up, which helps to achieve high accuracy of the results. For the case of radially symmetrical objects a numerical method is presented for calculating the refractive index distribution from data measured with the above mentioned type of differential interferometer. The results of a demonstration experiment are shown and further applications of this differential interferometer are discussed.
TL;DR: In this paper, an indigenously developed electronic circuit for identifying all the flow regime transitions in a vertical upward gas-liquid two-phase flow is reported, which basically converts the void fraction signal of the two phase mixture into a series of square pulses of varying width.
Abstract: A new method using an indigenously developed electronic circuit for identifying all the flow regime transitions in a vertical upward gas-liquid two-phase flow is reported. The circuit basically converts the void fraction signal of the two-phase mixture into a series of square pulses of varying width. The probability density function of the pulse width spectra is analysed for detection of bubble-to-slug flow transition. Slug-to-churn flow transition is detected on the basis of liquid slug length measurements. Churn to annular flow transition is identified on the basis of the number of liquid bridging. Experimental analysis shows that, in bubble flow through narrow tubes, bubbles bigger than a critical size cannot exist without forming Taylor bubbles. The technique has potential to minimize substantially the adverse effects of electrode polarization, stray impedance and varying conductance of the liquid medium. The sampling time and sampling frequency can be varied independently. The circuit can be used for measurement of both conducting and dielectric fluids.
TL;DR: In this article, an electronic speckle pattern interferometer (ESPI) using stroboscopic illumination from a diode laser, and its application in vibration measurement, are described.
Abstract: An electronic speckle pattern interferometer (ESPI) using stroboscopic illumination from a diode laser, and its application in vibration measurement, are described. Diode lasers are readily frequency (FM) and power modulated (AM) via control of their injection current; they are inexpensive and compatible with the single-mode optical fibres used in the described system. However, their modest peak power output demands the use of high-duty-cycle pulses, so that it was necessary to synchronize the illumination with the turning points of the vibration. This was achieved by operating the ESPI system in conjunction with a laser vibrometer. Injection-current-induced FM of diode lasers is non-uniform for modulation frequencies less than about 10 MHz, and to achieve successful stroboscopic illumination an electronic equalization stage was included to shape the current pulse, and hence compensate for the non-uniform FM.
TL;DR: The device's propenies of force detection, spatial resolution, object slip detection and a method for reducing the sensork uoss sensitivity to other influences are described.
Abstract: The requirement for a low cost, lightweight and robust force sensor for dextrous artificial hands or robot manipulators has produced a variety of different solutions. This paper describes one sensor, based on the transverse Hall effect. The device's propenies of force detection, spatial resolution, object slip detection and a method for reducing the sensork uoss sensitivity to other influences are described.
TL;DR: In this article, a stylus instrument is modified with a feedback system that allows control of the force from freely suspended to 10 mN and of the damping ratio from 0.02 to larger than one.
Abstract: This paper reports on the modification of a stylus instrument for studying dynamic effects in surface finish measurements. A feedback system allows control of the force from freely suspended to 10 mN and of the damping ratio from 0.02 to larger than one. Specimens of mild steel and copper have been traced repeatedly with damping ratios of 0.02 and 0.59 over the traverse speeds of 0.05-1 mm s-1. From these profiles it is observed that more consistent profile shapes and surface finish parameters are obtained within an optimal damping range. The performance of the system is investigated over a large range of damping ratios by freely suspending the system while applying a force proportional to a previously measured profile. The closest correspondence between the stylus output and the original profile, taken to represent optimal fidelity, occurs with damping ratios in the range of 0.5-0.7. Dynamic forces at the stylus are evaluated by direct measurement using a load cell and by indirect estimation through friction measurements. To compensate the additional mass due to the force actuator and damping sensor, it is demonstrated that the state feedback control can be used to vary the natural resonant frequency and the damping ratio independently.
TL;DR: In this paper, the performance and mechanical properties of an inverted pendulum as a vibration isolator were investigated for an interferometric gravitational wave detector and the advantages of such a system for vibration isolation was demonstrated through modelling of the isolator's response.
Abstract: The authors report the performance and mechanical properties of an inverted pendulum as a vibration isolator. The advantages of such a system for vibration isolation in an interferometric gravitational wave detector is demonstrated through modelling of the isolator's response. An experimental investigation using a prototype inverted pendulum was also performed where the behaviour of the stability, resonant frequency and Q factor with varying load mass was examined. The pendulum was also used as a seismometer to examine low-frequency seismic activity.
TL;DR: In this article, a photoelastic modulator in series with a Babinet-Soleil compensator (phase shift gamma ) and an analyser (adjustable orientation beta ) is used to measure the Kerr rotation, theta K and ellipticity in K of magnetic thin films.
Abstract: Kerr rotation, theta K and ellipticity in K of magnetic thin films are measured using an optical set-up including a photoelastic modulator in series with a Babinet-Soleil compensator (phase shift gamma ) and an analyser (adjustable orientation beta ). According to Jones matrix analysis two equivalent calibration procedures of the theta K and in K values are proposed. In one method these may be determined by controlled tuning of beta and gamma respectively in the conventional compensation mode. On the other hand, in a novel two-angle method, they directly emerge from intensity ratios recorded at two distinct settings of beta and gamma respectively. Exemplary data on alloyed films of MnBi(Al,Si) are presented.
TL;DR: In this paper, a new driver circuit for the electrochemical quartz crystal microbalance (EQMB) is described, which permits monitoring of in situ changes of the resonant frequency and of the quartz crystal equivalent resistance R'.
Abstract: The frequency change of an electrochemical quartz crystal microbalance (EQMB) is a function of both the rigid and the viscous masses coupled to its surface. The viscoelastic properties of the contacting medium define the mechanical loss of the vibrating quartz, which is characterized by the resistance R' in the equivalent electrical circuit. A new driver circuit for the EQMB is described. It permits monitoring of in situ changes of the resonant frequency fs and of the quartz crystal equivalent resistance R'. Thus this set-up allows one to distinguish between the rigid and viscous masses. Results obtained in different media with a prototype are discussed.