Table of contents

Liquid-crystal thermography based on wide-band liquid crystals, a colour-video system and a new vacuum bonded composite laminate is used to provide full-field, highly accurate wall-temperature measurements. In a prototype experiment natural convection heat transfer at an inclined flat plate in the presence of longitudinal vortices is investigated. The local distribution of heat-transfer coefficients is compared with the results of a numerical analysis.

An optical method based on laser scattering and optical triangulation for measurement of surface roughness and micro-displacement measurement is proposed. The technique allows evaluation of surface roughness and micro-displacement of a specimen using just one device. The principle of the method and the basic instrumentation design are described and the validity of the principle is demonstrated by experimental evaluations. Results show that, for specimens with surface roughnesses (R_a ) in the range 0.005 - 0.1 µm, displacements in the range ±300 µm can be readily measured.

We describe an optical method based on laser-induced fluorescence for obtaining instantaneous measurements of density along a line in low-density air seeded with I₂ . The Cordes bands of I₂(D ¹_u⁺ X ¹_g⁺) are excited with a tunable ArF excimer laser. Air densities in the range (0.1 - 6.5) × 10¹⁷cm^-3are measured over 295 - 583 K using the density-dependent emission ratio of two emission bands of I₂ ; the 340 nm bands and the diffuse-structured McLennan bands near 320 nm.

The blades are crucial components of the Virgo super attenuators. The material used for their construction is maraging steel, a low-carbon-content alloy with high ultimate tensile strength and low creep under stress. Young's modulus, the shear modulus, the Poisson ratio and the corresponding elastic energy-loss coefficients have been measured. The measurements have been performed on specimens subjected to the same thermal treatments as those of elements for the Virgo interferometer realized with maraging steel. In addition, anelastic properties of the material subjected to different thermal treatments have been measured. It has been found that, for a maraging-steel structure (one free of plastic deformation), which undergoes an excitation with flexural vibrations, the elastic energy-loss coefficient can vary over a wide range as a function of the thermal treatment of the material and it is dominated by the thermo-elastic effect. The main reason for such a great alteration is supposed to be the dependence of the thermal conductivity on the average sizes of the precipitate particles and their relative separations.

A laser tracking interferometer system developed by us is capable of measuring the coordinates of a target retroreflector. In this system, a self-calibration algorithm is used to determine system parameters such as the arrangement of laser trackers and the initial lengths of interferometers. The self-calibration algorithm is a least-squares method, hence in the algorithm a residue of measurement results is evaluated as a criterion of convergence. The relationship between the measurement error and the arrangement of the laser trackers was experimentally investigated. On the basis of these investigations, a new definition of the residue used in the self-calibration algorithm is proposed.

A robust and stable x-ray collimator has been developed to produce a parallel beam of x-rays by total external reflection from a parabolic mirror. The width of the gold-coated silica mirror varies along its length, which allows it to be bent from a plane surface into a parabolic form by application of unequal bending forces at its ends. A family of parabolas of near constant focal length can be formed by changing the screw-applied bending force, thus allowing the collimator to cater for a range of wavelengths by the turning of a screw. Even with radiation with a wavelength as short as that as Mo K₁( = 0.07 nm), a gain in flux by a factor of 5.5 was achieved. The potential gain increases with wavelength, e.g. for Cu K₁radiation this amounts to over a factor of ten.

Chromaticity based monitoring methodologies have evolved from polychromatic optical fibre based sensing systems, which was first implemented during the 1980s. The evolution has led to a recognition that such a methodology is applicable to monitoring systems more widely. It is shown that the method may be regarded as the manifestation of a particular form of signal representation by Gabor transforms. Examples of generically different practical implementations of the chromatic methodology to a range of different monitoring situations are given.

A nitrogen dioxide point sensor, based on a novel nondispersive gas filter spectroscopic scheme, is described. The detection scheme relies on the fact that the absorption spectrum of nitrogen dioxide in the 400-550 nm region consists of a complicated line structure superimposed on an average broadband absorption. A compensating filter is used to remove the effect of the broadband absorption, making the sensor insensitive both to small particles in the optical path and to potentially interfering gases with broadband absorption features in the relevant wavelength region. Measurements are obtained using a remote optical absorption cell that is linked via multimode fibre optics to the source and detection optics. The incorporation of blue light emitting diodes which spectrally match the nitrogen dioxide absorption allows the employment of electronic (instead of mechanical) switching between optical paths. A sensitivity of better than 1.0 ppm m column density (1 s integration time) has been observed; improvements in electronics and thermal stabilization should increase this sensitivity.

We have carried out photoacoustic measurements of the thermal diffusivity on samples of laboratory produced chemically bleached wood pulps, as well as on samples of several commercially available papers. Our results for bleached pulps indicate that the thermal diffusivity is correlated to each of the chemical bleaching controlling parameters (the kappa number, viscosity and brightness) measured during distinct phases of the bleaching processes. Also, the values of the thermal diffusivities for the commercial papers were found to be adequate for their end uses. It turned out that photoacoustic measurements can be a valuable research laboratory and/or industrial plant tool for comparing and controlling the properties of pulp and paper and for evaluating the effects of processing parameters upon these properties.

Ultrasound has potential to be used as a process monitoring tool alongside other techniques, such as pH, conductivity and dielectric measurements, tomography and optical turbidity. This paper outlines the development of a small volume test cell designed to monitor crystallization from solution in real time using low power ultrasound. The associated software is described and a series of experiments that have been carried out on a crystallizing orange reactive dye (BASF plc) are presented. Ultrasound has been used to monitor the crystallization process and the measurements yield data that separate into two distinct groups. These correspond to whether the dye is stirred or unstirred whilst crystallizing. Optical microscopy shows that well-dispersed crystals or extended networks of closely associated crystals are formed respectively. It was not possible to determine the principal physical constants of the crystallizing material due to its nature, so detailed theoretical modelling of the crystallization could not be achieved. Nevertheless, the phenomenological results indicate that the technique has potential to be incorporated into rugged instrumentation for monitoring crystallization in an industrial process environment.

Hydrogen concentration measurements were developed for a series of experiments in which a molten oxide is mixed with water to study vapour explosion phenomena. The gas mixture to be analysed consisted of hydrogen with water vapour and either helium or argon. Two types of sensor have been developed for these tests. The first is an ultrasonic sensor, which detects variations in the acoustic velocity within a 0.4 mm-diameter palladium wire. The sensor measures hydrogen concentrations in the range 0.1-100%, at atmospheric pressure, over an operating temperature range of 200-400 °C. The response time (for 0-90% of the final response) is about 30 s at 180 °C and 8 s at 380 °C. The second sensor consists of a palladium coil, constructed with 0.05 mm-diameter wire that is wound around a ceramic tube. Measurements of wire resistance were used to detect partial pressure of hydrogen. This sensor operates at 150-300 °C and measures hydrogen concentrations of 1-100%. The response time is short, 1-2 s for a temperature of 300 °C.

Screen-printed lead zirconate titanate (PZT) layers offer possibilities both for sensing and for actuation applications. The reaction between PZT and silicon during the high temperature sintering phase is a problem when combining PZT layers with silicon microelectromechanical systems. In this study we investigate a range of longer, lower temperature firing profiles for thick-film PZT, to reduce this reaction. Methods of measuring the d₃₃piezoelectric coefficient of thick-film PZT layers are reviewed and the test rig used to compare samples is described. Temperatures below 800 °C are found to be insufficient to produce sintering. At other low temperatures, longer firing times are found to be necessary in order to produce consistent results. A temperature of 800 °C for 8 h was found to produce a reduction in the level of reaction, without a serious reduction of the piezoelectric activity.

Ekman and Nurse's load-stepping approach to phase-shifting photoelasticity (1998) is able to determine automatically the isoclinic and isochromatic parameters. A problem associated with this method is that, because of the small load increments used, it is difficult for the user to obtain three accurately equal-stepped loads even with a rather precise loading rig. This deviation between two load increments then has a direct effect on the accuracy of the results. Also, experiment shows that this method does not work well for low stressed regions because the phase differences between loads are too small. In view of this, a modified approach to load stepping is proposed and is called the three-load method. This new method uses the relationships of phase retardations at each point for three different loads to determine the isoclinic angle θ in the range -π/2 < θ < π/2. Then the isochromatic parameter can be determined unambiguously. This method is easy to carry out and basically retains the accuracy of the phase shifting technique except for the change in sign of the parameters in the ambiguous regions.

A scanning facility for studying the thermoelectric behaviour of the metals used in elemental thermocouples (Au, Pt and Pd) is described. The facility effectively measured changes in Seebeck coefficient along a 560 mm length of each of three wires, relative to a fourth, by moving them through a 50 mm long, EMF-producing zone into a uniform-temperature region at 250 °C. The uniform region was stable to within 0.7 mK and EMF measurements were made to 10 nV (equivalent to about 1 mK). Accordingly, the facility is able to detect changes of ~10 ppm in Seebeck coefficient. The precautions necessary to work at this accuracy are detailed and preliminary data on the changes that occur at temperatures up to 1000 °C are reported. For example, the measured Seebeck coefficient of Pd decreased at temperatures in the range 550 to 850 °C, a change opposite in sign to that previously reported.

A narrow band near-UV backlight source with application in a new type of liquid crystal display is described. The light source is a pulse driven, mercury-argon gas, low-pressure discharge lamp. Pulse driving and lamp filling conditions are described for a lamp for which the ratio of the radiant outputs at 365 and 254 nm is enhanced considerably compared with the same lamp when it is operated with a conventional ac ballast. Pulsed operation of the lamp is shown also to increase the absolute radiant output of the group of transitions near 365 nm compared with the respective radiant output power from the same lamp when it is operated with ac with the same total input power.

We report on the use of an active Langmuir probe with three-harmonic compensation to diagnose rf discharge plasmas driven at 13.56 MHz. The plasma generates many harmonics on the fundamental, the first few being strongest. This gives a multi-harmonic rf voltage across the probe sheath that is removed by applying a rf signal to the probe that is matched both in amplitude and in phase for each harmonic. The probe I-V characteristic can then be analysed using dc theory. We show here that only when the rf harmonic amplitude approaches about 2T_e is it necessary to compensate for that harmonic. For the commercial processing rig used this only occurs for the second harmonic at low pressures, < 5×10^-3 mbar. Here the addition of second-harmonic compensation shifts the probe I-V curve, making it markedly more positive than for fundamental-only compensation. Despite this the values obtained for the electron density n_e and temperature T_e changed by less than 10%. For most plasmas in which the harmonics have amplitudes below T_e the use of fundamental-only compensation is adequate for all but the most precise measurements.

Despite the widespread use of the electrochemical quartz crystal microbalance (EQCM), there is still no commercially available instrument of the rotating type. The first reported rotating EQCM (REQCM) was built in the authors' laboratory in 1994 and, in 1997, a second generation instrument was designed to overcome problems with stability and sensitivity. This paper describes the design and construction of a rotating EQCM, detailing how these problems can be minimized. The advantages of this equipment are its high sensitivity ( < 10 ng), the ability to study reactions over relatively short time intervals and the possibility of studying electrochemical reactions which occur simultaneously with the evolution of gas. In this paper, the benefits of the REQCM are illustrated using two simple examples: the deposition of copper from cyanide solutions; and the leaching of copper in cyanide solutions. For deposition reactions, the REQCM effectively extends the electrochemical window, allowing the reaction to be studied simultaneously with evolution of hydrogen. Use of the REQCM is the only technique capable of achieving this. For leaching, use of the REQCM is the quickest, simplest and most accurate method of measuring reaction kinetics and determining whether a reaction is chemically or diffusion controlled.

This paper describes the experimental imaging of a spherical particle diffraction pattern obtained in back, forward and side scattering configurations, using illumination from three different beam shapes. The experimental problems encountered for each of the viewing configurations and the theoretical analysis of the diffraction pattern of the particle on its image plane using the generalized Lorenz-Mie theory are discussed. The images obtained are quantitatively compared with calculated results and implications for particle position estimation are discussed.

A long series of simulations of hairpin-filament guns as used in electron spectrometers was performed for filament-anode distances from 2 to 10 mm and acceleration voltages from 10 to 100 V using Child's law approximation, space-charge effects and rotational symmetry. The role of the Wehnelt electrode is clarified. Two distinct operation modes, the laminar (with positive Wehnelt voltages) and scrambled (with negative Wehnelt voltages) modes, are described and, for each, typical equations for the dependence of the current on the filament-anode distance and anode voltages are given.

This design note describes an experimental device, based on a Setaram C-80 calorimeter and an Anton Paar 512P densimeter, developed in order to measure densities and heat capacities at constant pressure of liquids and of liquids with gas dissolved. Pressure ranges from 0.1 to 70 MPa for the density measurement and from 0.1 to 100 MPa for the heat capacity determination, at temperatures from 303 to 473 K. The specific arrangement incorporated in the apparatus and the method of transfer of samples into the measurement vessels required for the study of these mixtures are also detailed. The functioning of this instrument was tested by measuring the heat capacity of liquid n-hexane, with calibration performed with water. Comparison with literature data obtained by an indirect method indicates that the deviation is less than 0.6%. The results of an investigation of a binary mixture, of n-decane and carbon dioxide, which has two phases under normal conditions, is also given.

A linear resistance-to-time (R -t ) converter consisting of a bridge amplifier and a comparator is described. While possessing a high order of resolution and linearity as a recently reported R -tconverter, the present circuit has the advantage of being simpler, insofar as it employs one op-amp less. Furthermore, the offset period is adjustable by a single element, without this affecting the sensitivity. Experimental results are given in support of the theory.

The laser induced pressure wave propagation method is often used to measure the space charge distribution in solid insulators. This method gives rise to many advantages, so it is widely used both in industrial and in research laboratories. However, it is necessary to take some precautions before treating induced signals in order to minimize calculation errors. Here, some quantitative information about the effects of approximations and the technical problems arising from this method used to study cable insulators are presented. Data from semiconductor/polyethylene samples have been obtained. Some recommendations defining an appropriate experimental protocol of space charge measurement in high voltage cable insulators are given.

In this design note we describe a simple circuit that can control and acquire many commercial CCD sensors by using a simple interface based on the enhanced parallel port (EPP-IEEE1284 protocol). Simplicity, low cost, high speed, immunity to noise and convenient software control are some of the advantages that make the proposed interface ideal for physics experiments and machine vision applications.

Figures 3(a) and (b) of this paper were mistakenly repeated instead of figures 3(c) and (d). The whole figure appears again below.

Figure 3. Effects of the scan length on (a, top left) s_Pa, (b, top right) s_Pb, (c, lower left) s_Pz and (d, lower right) s_Pt.

For the last six years, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of the journal believes that awarding such a prize is an opportunity to say `thank you' to authors for submitting their best material, and serves as a focus for their on-going quality review.

The working party, composed of R J Dewhurst, P P L Regtien and M A Player, considered a large number of papers recommended by Board Members. We would like to thank Board Members for their responses that formed an important part of the assessment process. We drew up a short-list of nine papers from the Board Member responses we received.

We re-examined these papers, with a view to finding an original contributed paper that described new and significant work, and that was presented in a clear and rigorous way. We also considered the referee-assigned quality ratings of the papers, and the number of accesses made to the papers in the Electronic Journal. We specifically excluded review papers, or papers appearing in special issues or special features that were of a review nature.

After lengthy discussions, we present the 1999 Best Paper Award to the following paper:

J Krupka, K Derzakowski, M Tobar, J Hartnett and R G Geyer Complex permittivity of some ultralow loss dielectric crystals at cryogenic temperatures10 387-92 (published May 1999)

The award, comprising a cash honorarium and plaque, will be presented to the author at a suitable venue in the near future.

The paper describes the measurement science and technology required to conduct measurements of permittivity and the dielectric loss tangent in low-loss crystals down to 4 K. It provides a clear description of the techniques used. The quality of the data, together with comparison of values from previous published work, vindicates their measurement claims. The results presented establish a very accurate (with 0.1% tolerance) permittivity versus temperature database for a number of low-loss crystals, e.g. sapphire, YAG, quartz and SrLaAlO₄, in the 10-20 GHz region. Tan δ measurements down to 10^-8 are presented. In addition, the paper contains a solid set of references and draws together a concise set of conclusions as a summary.

We also short-listed a further three papers for the award:

T Schmitz and J Ziegert A new sensor for the micrometer-level measurement of three-dimensional, dynamic contours10 51-62 (published February 1999)

M Höbel and K Haffner An on-line monitoring system for oil-film, pressure and temperature distributions in large-scale hydro-generator bearings10 393-402 (published May 1999)

S Yokoyama, J Ohnishi, S Iwasaki, K Seta, H Matsumoto and N Suzuki Real-time and high-resolution absolute-distance measurement using a two-wavelength superheterodyne interferometer10 1233-9 (published December 1999)