Table of contents

The Bayesian statistical theory of measurement uncertainty, recently developed to form a mathematical foundation of international recommendations, is applied to the problem of deciding whether or not two measurement results y₁ and y₂ of the same measurand conform with one another, taking into account the uncertainties associated with the measurement results. Four conformity criteria proposed within the framework of the theory are discussed and compared with three commonly used criteria based on conventional statistics and the least-squares method. All the criteria turn out to be essentially equivalent to one another. They all yield the conformity condition mod y₁-y₂ mod <or= beta s but with different suitable numbers beta in the range from 1 to 3. s is a standard deviation expressing the uncertainty corresponding to the difference y₁-y₂.

We present a data-acquisition system for a high-power pulsed Nd:glass laser oscillator-amplifier chain. This system includes a number of laser energy monitoring units at various stages of the laser chain, a data-acquisition unit and a control program to control its operation. Each unit in this system is modular and versatile. The system is also capable of working in the presence of high electromagnetic interference, as is found in operation of high-power pulsed Nd:glass laser systems. Any component of this system can be modified independently of the others if the system requirements are changed. The system is ideally suited for lasers with low repetition rate of operation.

A smart sensor is a device whose response takes into account and corrects for environment variables. This study shows that such a device can be produced. The major influential variables studied were temperature and humidity. The sensor was a sensitive coil inserted in an LC oscillator circuit. Oscillator operation was improved to obtain sufficient stability. Data were acquired on a testbench. Although the measurements were distorted by many phenomena (noise, dilation and so on) it was quite possible to design a displacement measurement smart sensor, based on several theoretical models. They predict a frequency response versus distance and temperature. The experimental results were in good agreement with the models.

A new method for measuring the self-heating and response time of resistance thermometers is presented that can be applied to thermometers installed in situations where the temperature may be fluctuating and/or drifting with time. A technique developed for mass comparisons is used to analyse a sequence of ten indicated temperature measurements recorded with sensing currents I₁ and I₂ in the sequence (I₁I₂)₅. Self-heating values are obtained with sub-millikelvin accuracy using standard equipment from self-heating changes of less than 1 degrees C. The response time of the installed resistance thermometer is obtained by repeating this sequence of measurements as a function of the delay between changing the sensing current and measuring the indicated temperature.

The application of phase shifting interferometry to the study of thin soap films is presented. A precision optical cell for film production is described, and the measuring sequence is detailed. Representative results on a known surfactant are also given.

In optical microscopy, as in many fields, it is sometimes necessary to observe and study phenomena that occur over very narrow temperature ranges. For this purpose a temperature controller and heating stage have been developed for use in optical microscopy with an average temperature stability within +or-2 mK. The temperature can be varied from sub-ambient temperatures up to 373 K. The temperature controller is also interfaced to a personal computer via a 16-bit digital to analogue converter which allows remote control and the heating stage to be heated and cooled at predetermined rates.

Two modifications of trochoidal electron analysers are proposed. The first uses the non-uniform electric field at the half-plane electrode edge. The optimum conditions of electron transmission are determined from the equations of motion. The analytic expressions for similarity laws are derived in a drift approximation. The second modification uses a geometry close to that of a conventional trochoidal monochromator. Two half-planes with a narrow strip in a gap between them are used instead of one solid plane electrode. In this case, the optimum conditions are found numerically and plotted graphically. In comparison with the non-uniform field analysers developed previously, the analysers being proposed possess an important advantage, namely the simple shape of their electrodes, their improved performances appearing quite similar.

This paper describes a control system developed for acquisition of sequences of multi-exposed images, the goal being acquisition of quantitative information from flow visualizations obtained by laser tomography. The basic equipment consist of a camera equipped with a light intensifier and an electronic shutter. The video signal of the camera is digitized by an IBM personal-computer-compatible frame-grabber. The control system is designed to synchronize the activity of the different equipments of the process: camera, shutter, frame-grabber and flow generator. Different parameters can be defined: number of images to be acquired, number of expositions, each exposure and shut-down time, delay between flow generation and image acquisition. These process parameters are transmitted through a serial line by a program developed in the Windows environment. For one frame, exposure and shut-down times can be defined with a precision of 1 mu s. These different times are generated by a sequencer obtained with programmable logical devices. The system is not specific to fluid mechanics; it can be used for quite a lot of problems that show rapid changes.

A digital double-exposure speckle system is developed for in situ measurements of in-plane displacements or deformations. A fast Fourier transform algorithm with an inexpensive computer is applied to obtain fringe patterns of Young's type: some applications of the method to stone samples under mechanical stresses, for determining the extent of movements in the vicinity of pre-deteriorated areas, like cracks, are reported.

An investigation of the degradation of the line spread function due to electron scattering in a micro-channel plate intensifier employing a semi-transparent photocathode and proximity focusing is reported. Data obtained using the Anglo-Australian Telescope (AAT) are used to measure emission line broadening and infilling of absorption features in astronomical spectra, due to scattering in the micro-channel plate intensifier. A comparison with a magnetically focused four-stage cascade intensifier is made. Values are obtained with the two intensifiers for equivalent width and residual infilling of a totally saturated absorption feature. The micro-channel plate intensifier is found to scatter into the wings of emission lines a larger fraction of the input signal than the cascade intensifier, amounting to 6.5% of the total signal. A model of the line spread function degradation observed in the micro-channel plate intensifier, based on electron scattering in the input proximity focused lens, is also presented. The modified line spread function obtained from this model is found to be a remarkably good fit to the data obtained at the AAT, and the values for infilling of absorption line features calculated from the model are close to those observed in the spectra. Finally, suggestions are made as to how the design of future micro-channel plate intensifiers can be modified to reduce scattering from the input micro-channel plate.

We report on the design and performance of a hollow-cathode discharge continuous wave He-Cd⁺ laser module, which is capable of simultaneously delivering stable, milliwatt power output at the three primary spectral lines blue, green and red. A mixture of these lines can result in a wide band of colours, including white light. The laser can be formed from one or more laser modules. A module consists of two anodes with a hollow cathode located between them. Two long, narrow cylinders (50 mm long, 4 mm in diameter) separated by a wider cylinder (10 mm long, 10 mm in diameter) are made in the hollow cathode. The narrow cylinders serve as hollow cathodes, while the wider cylinder efficiently stabilizes the discharges in the narrow cathode cylinders, making them spatially similar. Owing to this particular cathode design the laser module, with a 10 cm active length, stably and effectively lased at seven wavelengths in blue ( lambda =441.6 nm, 3 mW), green ( lambda =533.7 nm, 0.3 mW; lambda =537.8 nm, 0.4 mW), red ( lambda =635.5 and 636.0 nm, total 0.2 mW), and infrared ( lambda =723.8 and 728.4 nm, total 0.1 mW). The optimum He pressure, Cd vapour pressure and cathode current were 8 mbar, 0.01 mbar (corresponding to a cathode temperature of 533 K), and 260 mA, respectively. The short- and long-term laser output power variations were less than 1% (peak-to-peak). The laser has exhibited stable operation for 300 h without discharge deterioration. The above allows us to claim that the presented hollow-cathode discharge continuous wave He-Cd⁺ laser module should be useful as a simple, short, long-lived, multicolour laser source, operating at milliwatt output power levels. However, for higher output power level demands (tens of milliwatts) three or four laser modules must be used.

An optical diffraction method has been applied to determine the diameter of metal wires. A simple technique using position-sensitive detectors has been developed to inspect the diameter of metal wires with the possibility of being employed on the production line, in which the wires may drift randomly with some adverse factors such as vibration and air movement.

The experimental set-up for investigation of the rotational and vibrational state distribution of desorbing hydrogen molecules is described. Resonance enhanced multiphoton ionization is applied for this purpose. In a (2+1) process hydrogen molecules are excited into the E, F state and subsequently ionized. Detection of the ions is accomplished by the use of a time-of-flight spectrometer. Performance of the set-up is demonstrated on hydrogen molecules desorbing from nickel using a permeation source. Quantitative determination of the quantum state distribution is attained by comparing the data to the resonance enhanced multiphoton ionization spectra of a Knudsen source. The experiments revealed rotational cooling of the desorbing molecules but no significant change in the vibrational state distribution.

In this paper, the authors have developed a phase-domain model to analyse a nonlinear fibre-optic gyroscope system theoretically, and use it to obtain the optimally designed system with a second-order controller. From computer simulations and experimental results, one can design a fibre-optic gyroscope system with optimal performance specifications, such as steady state accuracy, percentage overshoot and rise time; ensure that the optimal second-order system is superior to the optimal first-order system in both steady state error and dynamic responses; realize a highly stable second-order fibre-optic gyroscope system with fast response and less overshooting; and optimize it without trial and error efforts.

The use of sound from laser-induced, dielectric-breakdown-generated transient plasma as a signal for testing ultrasonic air transducer reception response was studied. The test signal takes the form of an acoustic impulse that is caused by the rapidly expanding plasma. The ultrasonic air transducer's receiving response and relative sensitivity can be quickly characterized using this method. The advantages that this method offers are speed and the fact that no calibrated wideband signal source is needed. Therefore it would be suited for fast, on-line mass testing of air ultrasonic transducers.

The traditional hot-probe method, which is developed from the transient hot-wire method, can only be applied to determine thermal conductivity. This kind of method is based on the idealized 'one-dimensional radial heat flow' model. As a matter of fact, the finite length influence of a hot probe on measurement is remarkable when the hot probe is not sufficiently long. The corrected term of finite length for a hot probe is nonlinearly dependent on the thermal diffusivity of the measured sample and the length of the hot probe. In this work the long/short hot-probe method (LSHPM) is developed which can simultaneously determine the thermal conductivity, thermal diffusivity and specific heat of the measured sample. The basic principle of the LSHPM is analysed, the measurement procedure is described, and the relative differences of the measurement results are compared with the values recommended by the Thermophysical Properties Research Center, which are 0.7%, 1.3% and 2.0% for thermal conductivity, thermal diffusivity and specific heat respectively.

The Gaussian beam defect is now a well documented deficiency of conventional phase Doppler anemometers and leads to significant errors in particle size estimation when the particle size takes on dimensions of the same order as the measurement volume. In the present paper, an alternative operation mode of conventional, two-component phase Doppler anemometry systems is proposed, which removes these errors for many applications. The new approach is analysed theoretically and its improved performance is verified experimentally. Furthermore, the effect of a slit aperture on the trajectory-dependent size measurement has been experimentally investigated.

A compact scanning probe microscope for operation in air and liquid is described. The probe techniques implemented are scanning tunnelling microscopy and scanning ion conductance microscopy. The software, electronics, mechanical construction and some representative measurements are presented. The compact and concentric microscope head is built around a commercial piezoelectric inchworm motor. The scanner is a standard piezo tube. An analogue feedback system is used for taking images, while digital control of the probe-sample distance is used for other experiments, such as measurements of current-voltage characteristics. A Macintosh personal computer is used for control and presentation of data. A simple method to make scanning tunnelling microscope tips suitable for electrochemical use is described. The microscope has a high resonance frequency (9.6 kHz), low noise (0.01 nm Hz^{- 1}2 / at 10 Hz), low thermal drift (less than 0.1 nm min^-1), and high acoustical noise suppression. The current-distance-dependency of the scanning ion conductance microscope was found to be linear.

A simple apparatus for measuring electrical conductivity under pressures up to 1500 bar was developed in order to study the electrical behaviour of microemulsions as a function of pressure. Details of the construction of the cell are indicated. The first results obtained on the phenomenon of percolation as a function of pressure are presented.

We propose an appropriate calculation method, giving both the complex permittivity epsilon * and permeability mu * of a liquid sample, from transmission/reflection measurements obtained from a network analyser working on a coaxial line between 0.1 and 20 GHz. A 20 mm long specific coaxial cell has been constructed using two polytetrafluoroethylene joints to ensure air tightness. Its small length allows rejection towards the upper frequencies of the measurement anomalies given by the Nicolson-Ross equations. Positions and thickness of the joints are taken into account by the calculus. The whole system has been tested with the empty cell and then on several alcohols and ferrofluids. The results on alcohols are in excellent agreement with all previous results; measurement on one of the magnetic fluids (Fe₂MnO₄ in CCl₄) has shown a Neel relaxation and also a gyromagnetic resonance.

Among experimental designs used to study microwave heating from a fundamental point of view, a simple robust and low-cost device is proposed to measure the permittivity of a test sample during irradiation. It works at 2450 MHz and its basic component is a six-port implemented in a rectangular waveguide. Before using the six-port as a reflectometer, without moving mechanical parts, the diode detectors of the six-port and the six-port itself are calibrated together with a sliding short circuit. The calibration takes into account all the unwanted reflections inside the device. The device was used with an applicator made for rod-shaped samples. To check it, measurements were made on water, lucoflex and polytetrafluoroethylene. An example of the type of results that can be obtained is given for moistened sand.

We present a software package developed on the LabVIEW platform which controls a synchrotron radiation experimental station for surface science experiments and allows users efficient use of the equipment. In contrast to other programming environments, LabVIEW offers programmers an effective way of integrating the functions of several real instruments in a virtual instrument. By means of GPIB and serial communication, our software controls most of the instruments attached to the experimental station. We developed programs (sub-virtual instruments) that allow interaction with the instruments by means of realistic-looking and -acting control virtual tools (knobs and buttons), which the user can 'handle' on the computer screen using the mouse. These 'virtual panels' allow simultaneous control of all the devices involved in a specific experiment, performing sequences of operations in an automated way. We present here the general principles of operation of the program, highlighting the advantages that this approach provides.

This paper presents a cheap thin film thickness monitor control unit for piezoelectric crystal heads. The output of the unit is a TTL compatible crystal frequency signal.

We describe an ultraviolet photon detector realized for parallel acquisition of eight inverse photoemission spectra in the isochromatic mode, at photon energies from 10 to 25 eV. This simple and reliable device is obtained by combining an array of eight channeltrons corresponding to the various photon energies of the spectral and a single Csl-coated photocathode.

A simple low-cost system having a modified pulling arrangement and a temperature controller for growing single crystals is described. The design and technical details of the system together with those of the temperature controller are described. The system is found particularly suitable for growing optically high-quality single crystals of materials of layered structure.

A new technique for quiet gradient coil design in magnetic resonance imaging is proposed. Preliminary results on a test coil show acoustic noise attenuation behaviour consistent with theory. Active acoustic screening will significantly reduce the dangers to patients of high-level exposure to noise in medical resonance imaging scanners.