Table of contents

The distribution of intelligence within a complex data acquisition and control system can result in significant improvements to the performance of that system, whilst also providing facilities that are difficult or impossible to attain using conventional techniques. The application and advantages of such distributed intelligence are reviewed and the capabilities of appropriate hardware are compared and evaluated. The importance of supporting software and development facilities is discussed. The authors' aim is to encourage novel applications that will benefit from relatively cheap, yet powerful, intelligent systems.

The authors describe a device that can resolve the average pressure exerted on a solid wall due to interactions with particles independently of the pressure exerted by fluid forces. The device has been used to measure the average particle pressures exerted on the walls of a gas-fluidized bed.

A simple designing method for linearizing circuits, based on one resistor, is presented. The errors caused by this circuit are calculated, considering the temperature range and the thermistor parameters. These errors are used as a basis for comparing the quality of active linearizing circuits. In many cases, complex circuits have similar errors to single resistor linearizing circuits. It is shown that the exponential approximation is one of the most important error sources. The authors propose to use more precise models. The relationship between the parameters of the exponential model and those of other models is discussed.

An experimental set-up for heat flux conduction calorimetry with improved applications in liquid mixture studies by continuous titration is presented. The experimental system is controlled by a personal computer. Sophisticated signal processing determines the partial excess enthalpies H_i^E or relative apparent molar enthalpies phi L_i over the entire range of concentration, including the high dilution domain (0.001<or=x_i<or=0.999).

The authors present experimental results concerning inductance variation of 'C'-type magnetic circuits for proximity sensors, as a function of different parameters: position and geometry of coils, magnetic circuit material, thickness of target, frequency of measuring signal, thermal hysteresis of magnetic circuits and some auxiliary construction elements (protective box, coating resins).

For testing high-voltage rectifiers and capacitor charging systems a power frequency source has been developed using readily available components in a series resonant circuit. The inductors are modified ignition transformers as used for oil or gas burners. The appropriate number of transformers is selected for the output required and tuned to resonate at 50 Hz with a separate bank of capacitors. Sustained voltages up to 100 kV RMS have been generated. Compared with single new transformers the cost is about 20% for 50 kV and 30% for 100 kV assemblies. The costs are those items which cannot readily be constructed in a nonspecialised laboratory workshop. The equipment is easily carried and assembled by one person. With rectifiers the system has been used successfully to supply up to 10 mA for charging capacitors to 50 kV. Extension to higher voltages is possible, the limit being set by the stray capacitance of the assembly.

A simple system that permits the surface separation to be varied smoothly and accurately in a surface force apparatus is described. It is based on the deflection of the force-measuring spring in a magnetic field gradient created by a current passing through two coils. The resulting displacement of the surface is highly linear with applied current and free of hysteresis over separations of 10 mu m or more. This allows the accurate measurement of the force between two surfaces by monitoring the difference between expected and observed spring deflection (using, for example, multiple-beam interferometry).

An NMR spectrometer is described which is capable of handling a wide range of experiments on abundant spins in condensed phases under low- and medium-resolution conditions. The control and RF units are interfaced to two separate magnet/probe systems. One is designed for relaxation or wideline experiments at temperatures within 50 K of ambient temperature whereas the other involves a cryogenic probe for studying samples at temperatures down to approximately 20 K. The spectrometer offers versatile pulse programming, flexible data manipulation and sophisticated statistical analysis. It is particularly well suited to observing ¹H lineshape and relaxation phenomena in samples which have a spin system that is heterogeneous in terms of molecular mobility, and to the determination of NMR parameters of molecules isolated in inert matrices at cryogenic temperatures. Some representative proton relaxation data are reported for samples of polypropylene. These show that the spectrometer system has adequate reproducibility and sensitivity.

The authors report a computer-controlled laser microfluorometer that is applicable to imaging cytometry. To obtain high sensitivity the system is equipped with a laser and an intensified photodiode array detector. The authors have observed spectra of low-level fluorescence emitted from micron-size regions in cellular specimens. For living cells of onion and carrot loaded with acridine orange and indo-1, respectively, fluorescence spectra with large signal-to-noise ratios were obtained at an exposure time of 0.1 s at a resolution of 1.4 nm and in the spectral range of 350-670 nm. The total acquisition time was about 15 s for a one-spot spectrum with 1024 spectral data. By scanning the illuminating micro-spot fluorescence images with a resolution of less than 2 mu m were obtained at a specified wavelength from the detected signal.

The authors are concerned with the interpretation of the instantaneous signals from an X hot-wire probe used for velocity component measurements. A detailed calibration study was carried out to identify the correct velocity and yaw response of a typical plated X hot-wire probe. The calibration data identified an accurate calibration relationship for the X hot-wire probe, and enabled the development of a related look-up inversion method. This provided a reference for the assessment of the accuracy of common signal analysis methods. Using a step-by-step approach, the errors caused by the assumptions of constant values for the offset and exponent in a power law relationship were first identified. Then, the errors relating to the introduction of the concept of an effective velocity V_eff and analysis in terms of V_eff² were determined and finally the errors in the sum and difference method based on V_eff. The authors demonstrate that these errors cannot be neglected, even at low turbulence intensity, if accurate flow measurements are required.

The response of inclined hot wires operated in the constant wire temperature mode to fluid temperature variations was explored experimentally over a range of incident angles from 5 degrees to 85 degrees . Results showed that the square of the output voltage varied linearly with fluid temperature as reported previously for wires normal to the flow. The slope of the plots of voltage squared against temperature was found to be a function of the effective velocity only, thus allowing implementation of a simple, instantaneous temperature compensation technique. An additional benefit of the method is that it can detect faulty wires.

The authors have determined the characteristic quantities (the electron temperature and the electron density) of an argon plasma in a cascade arc (diameter of 2 and 4 mm) for a pressure range of 1*10⁵-8*10⁵ Pa and a current range of 20-70 A. The absolute continuum intensity was also determined in the wavelength ranges from 250-320 nm and 380-800 nm for pressures of 2, 4 and 6 bar and 20, 40 and 60 A in the case of a 2 mm arc. The plasma is close to local thermal equilibrium (LTE). Using the mentioned quantities, prediction of the absolute intensity as a function of the wavelength is possible from 140 nm to the infrared within 10%. The use of the arc as a light source in photon induced chemical vapour deposition, spectroscopic ellipsometry and infrared absorption spectroscopy is discussed.

A procedure for extracting angle of incidence information from photographs of LEED patterns obtained with a conventional LEED optic is described. The method is sufficiently general to be able to deal both with a misalignment of the LEED optic with respect to the electron gun and with a sample positioned away from the centre of curvature of the LEED optic.

A new method of NMR imaging suitable for solids is introduced which takes advantage of the spatial selectivity of a specially constructed receiver coil. The probe consists of a homogeneous transmitter coil which is larger than the sample, and an inhomogeneous receiver coil which is only sensitive to a thin slice of the sample. An image is recorded as a function of the position of the sample in the receiver coil while applying a pulse cycle which eliminates all line broadening mechanisms. Since the spins experience no spatially dependent fields or interactions, the entire sample reacts uniformly to this experiment, and the only limitation to the obtained resolution is the spatial selectivity of the receiver coil. This approach is a candidate for slice selection as well as the 1D imaging for which it is demonstrated. Two- and three-dimensional extensions are discussed.

The values of Young's modulus and internal stress in boron doped silicon microresonators fabricated by anisotropic etching techniques are reported. An array of resonators has been fabricated on a (100) orientation substrate and their resonant frequencies measured. Using the measured data, and equations relating the resonant frequencies to mechanical properties, the Young's modulus of the boron doped silicon is calculated to be 1.33*10¹¹ Pa whilst the built-in stress is calculated to be 1.12*10⁸ Pa.

A simple AC susceptibility technique in a diamond anvil cell has been successfully used to detect the superconducting transition of high-T_c superconductors under hydrostatic pressure of up to 14 GPa. The system uses two radically balanced detection coils mounted inside the cell. Measurements have been performed on YBa₂Cu₃O_7-x for which T_c is found to decrease linearly with pressure above 2 GPa with a slope of -2.5 K GPa^-1 for single crystals and -1.1 K GPa^-1 for polycrystalline samples.

A technique for detecting superconductivity in small samples of high temperature superconductor is described. The sample is placed within the inductor of a Colpitts oscillator. The precise quantity of feedback is finely adjusted to maintain oscillation at a set amplitude. The presence of superconductivity is detected through a small but sudden change in frequency and an increase in the gain required to maintain oscillations. The value of critical shielding current may also be estimated in these experiments. The various modes of application of the technique are illustrated by typical experimental results.

The authors report the results of critical current density measurements in sintered YBa₂Cu₃O_7-y samples using different methods and interpretive models. Their aim is to describe the problems encountered when measuring intergranular critical current density, especially at low magnetic field values. These problems are due to the fact that J_c is strongly dependent on the magnetic field and the measuring methods in common use generally imply a non-uniform magnetic field value inside the sample. Under these conditions, measurements of J_c do not reflect a real value but a mean value which is heavily dependent on the form and dimensions of the sample. This makes it impossible to compare directly readings made on different samples. The authors suggest to interpret magnetization readings with a numerical simulation based on the 'critical state' model. They also offer an analysis of the signal induced in the sample as the best inductive method of measuring J_c irrespective of the shape or dimensions of the sample, within limits that they specify. They also consider the effects of clusters and the problems they cause in measuring J_c in samples where they are present.

A differential photopyroelectric (P²E) spectrometer using thin pyroelectric PVDF film, with real-time spectrum normalization measurement capability has been developed and characterized. The spectrometer is able to perform measurements as a function of wavelength (limited by the Xe lamp spectrum: 280-1960 nm) and modulation frequency (0.1-600 Hz). The authors describe the abilities and advantages of the photopyroelectric spectrometer over other photothermal spectroscopic instrumentation, and draw attention to different sources of possible experimental errors. Several experiments have been performed as a function of wavelength and/or modulation frequency in order to calibrate, characterize and optimize the working conditions of the photopyroelectric spectrometer. Some further measurements on c-Si have been performed in order to show the instrumentation capabilities. The present differential photopyroelectric spectroscopic technique seems to be very promising toward the characterization of semiconductor thin films and devices.

The basic architecture of a general purpose program that allows the simultaneous collection and analysis of data on a single-task personal computer is described.

An inexpensive sample holder for resistivity and Hall factor measurements is described. Its simple design prevents thermo-EMFS and makes its construction feasible in a short time.

An essentially all-metal cryostat employing a standard design Dewar and a couple of Araldite joints, for the deposition of thin films with substrates at liquid helium temperatures and for in situ studies, is described. Contrary to general opinion regarding the unsuitability of Araldite joints for vacuum systems, this system remains leak-tight even after numerous runs. The apparatus is especially useful for studying the electrical properties of amorphous multiple films-one deposited over the other, which are easily oxidized or contaminated on exposure to air.

A new design is presented for a multi-concentric coil structure capable of producing an axial magnetic field with an increasing magnitude which varies in a near-linear manner over almost the entire length of the complete solenoid arrangement. A design code has been developed and a complete solenoid conformation has been built from the specifications derived from this program. The measured profiles have shown good agreement with those predicted theoretically.