Table of contents

The assessment of instrument reliability using mathematical models based on field data or laboratory test results is discussed. Techniques are described for the prediction of the reliability of an instrument for which no failure information is available, and a distinction is drawn between total failure and calibration faults. The factors influencing the reliability required of an instrument are discussed. By the application of some simple design principles and use of redundancy and diversity where necessary, it is shown how an instrument or instrument system can be designed to a specified reliability target.

A compact double-channel nitrogen laser which permits the simultaneous pumping of two dye lasers, or a dye laser oscillator and a dye amplifier, is described. The characteristics of each emitted pulse are typically 200 kW and 5 ns.

Thickness measurements of thin films are often made with surface profile monitors. The preparation and optical measurement of a set of standards that will allow the calibration of a surface profile monitor to an accuracy of +or-1% are described. With these standards, it has been found that the use of calibration standards provided by the manufacturers of such monitors can lead to errors in thickness measurements of over 5%.

The optical apparatus described permits the measurement of the reflection coefficient R of an investigated sample at incident angles in the range from 8 to 90 degrees . The system is constructed from four plane mirrors and a spherical one. The light path in the apparatus is relatively compact. With aluminium mirrors the transmission of the apparatus is approximately 80%.

The design and operation are described of a multiple optical cell and supporting apparatus for making precise absorbance measurements of dilute aqueous solutions over the temperature range 25-374 degrees C. The advantage of the apparatus is that measurements on a series of solutions equilibrated together at high temperature can be made within 5 min.

The design is described of a linear expansion test rig which is invariant in length over a range of ambient temperatures. Results are given of a thermal and moisture expansion tests on a range of building materials.

By consideration of the heaters in a spherical calorimeter as delta-function sources, it is shown how the time constant to equilibrium, and hence the parasitic heat losses can be diminished.

The equations of motion for torsion pendulums for various model solids are briefly described. It is shown that the formulae for internal friction derived by Iwasaki et al. (1977) are only valid for the Voigt solids. Their criticism of the analysis of the composite torsion pendulum by Collette et al. (1961) is shown to be in appropriate; the original analysis by Collette is essentially correct. An alternative treatment of the Collette pendulum is presented.

The circuitry of the external photomultiplier incorporated in a Vacuum Generators hemicylindrical energy analyser has been modified to achieve a flatter background in the low-energy region of the derivative spectrum. Two methods are described which enhance the detectability of Auger electrons with energies below about 150 eV.

The object of this application of light pipes was to observe the motion, distribution, and evaporation rates of fuel droplets under conditions encountered in the early stages (before combustion) chambers were simulated in a pressurised chamber of nitrogen. Pressure and temperature were 1700 kN m^-2 and 720K. The technique is compared with other photographic methods.

An inexpensive, very simple, flexible microprocessor-based system has been designed for spectrophotometric data acquisition and paper-tape punch unit control. The interface circuit has been implemented with off-the-shelf components and a low cost development system has been used for software and interface development and testing 'in the field'. The system cam be easily adapted to similar instrumentation.

A miniature SQUID with two inductive loops and having application in a compact measurement system is described. This SQUID is used for total field measurement, is preset and provides a reliable, robust unit able to survive repeated thermal cycling over a long period.

When nuclear magnetic resonance techniques are applied to the imaging of structures deep inside the human body, it becomes important to consider the degrading effects of the surrounding body tissues on the signal-to-noise ratio of the received resonance signal. The passage of the NMR signal through the surrounding conductive tissue casues an appreciable loss of signal strength at high frequencies. Also, the presence of a large resistive medium, such as a portion of the body, inside the receiving coil causes a significant amount of thermal noise to be detected. The levels of the signal-to-noise ratio and the corresponding spatial resolution are quantitatively discussed in this paper. Expressions are obtained which enable the resolution to be estimated for a variety of medical imaging systems.

An electronic device is described which will maintain stress constant to within +or-0.1% during creep tests. The device is used in conjunction with conventional dead-load creep apparatus and, in common with all constant-stress methods, requires that the deformation of the test specimen occurs uniformly and at constant volume. The device is not strain-limited and will maintain stress constant even to the large strains characteristic of deformation in superplastic materials. Its performance compares favourably with the best cam lever machines currently available, with the advantages that the absolute value of the stress on a specimen may be calculated throughout the course of a creep test. Unlike cam lever machines, it can be used to test specimens of widely different gauge lengths with equal facility. Creep tests on 20%Cr/25%Ni/Nb-stabilised austenitic steel are described to illustrate the use of the device.

The design, operation and details of construction of a fully shielded microwave-integrated-circuit holder suitable for use with thin-film superconducting microstrip circuitry including couplers, filters, impedance transformers and devices such as Josephson junctions are described. Several simple microwave coupling schemes for use with Josephson junction 2e/h frequency-to-voltage transducers illustrate the flexibility of the microstrip approach for coupling to thin-film Josephson junctions and semiconductor devices at cryogenic temperatures.

The case where every particle which passes through the ellipsoidal probe volume produces one and only one velocity measurement is examined. The implications of this simplification are considered in detail. It is shown that it is usually possible to arrange the system parameters so as to justify this assumption, especially if frequency shifting is used for highly turbulent flows. The method of bias correction described applies to a one-dimensional LDA which does not measure particle residence times. This method involves fitting a theoretical biased probability density function of velocity to the experimental velocity histogram, and the mean and root mean square velocities are obtained by the maximum likelihood estimation procedure. This method requires estimates of two other properties of the turbulent velocity field, but it is shown that the results are not very sensitive to the values of these estimates.

A dynamic force balance has been developed for the measurement of the instantaneous lift and drag components of an insect flying fixed in a wind tunnel. The force balance is a simple taut 'string' with fixed ends; in this work a live insect is mounted near the string midpoint. The miniscule wire displacements due to imposed forces are optically detected and interpreted as forces by an electromagnetic calibration procedure. The system response is strongly frequency-dependent, but this posed no serious problem for the measurement of periodic forces such as lift and drag fluctuations due to wing beat.

An analysis is given of the possible advantages of a photoelectron spectrometer based upon the properties of the axially symmetric inhomogeneous magnetic field of a superconducting solenoid. The consequences of electron motion along the solenoid axis are discussed and it is shown that this can lead to a novel high-resolution method of electron energy analysis together with the possibility of photoelectron microscopy.

The instrument has a high sensitivity and a resolution of 25 meV. It is also shown that the range of analysed energy is about 1.5 eV. A further improvement of this instrument is still possible. To make sure that the interpretation of results is correct, calibration measurements were performed and compared with the theoretical electron energy distribution. High-emitting regions of a tungsten emitter with well known emission properties were used for calibration of the spectrometer.

X-ray powder diffraction patterns from four samples can be simultaneously recorded using a Guinier-de Wolff Camera. There are several advantages in using a four-sample camera, such as ease of direct sample comparison and the possibility of incorporating a calibrating substance independent of the unknowns. This paper describes a computer-controlled system which automatically scans the X-ray film, processes the diffraction data and lists the position and intensity of each maximum in the four samples. The reproducibility and accuracy of automated scans on NaCl and hydroxyapatite, Ca₅(PO₄)₃(OH), corrected for camera position and film shrinkage, are presented and discussed.

Describes a method for measuring the nuclear spin-lattice relaxation time T₁ by the free precession technique, which offers certain practical advantages, particularly in the measurement of relative values of T₁. The method is a simple modification of the original signal-growth technique of Carr and Purcell. Instead of measuring the time constant for the signal growth or the time required for the signal to go to zero (t_n), the method is based on measuring the signal heights at only two points on the growth curve-one below and the other above t_n. From theoretical considerations, it is shown that it is possible to determine this null point, and hence the relative values of T₁, with the desired accuracy by the correct choice of these two points. It is also shown that this method can be adapted to measure absolute values of T₁ with comparable accuracy. Some experimental results are presented to demonstrate the method.

An access control system is described using speech samples for an automatic verification of a claimed identity. A hardware speech analysis processor extracts spectral information from the utterance and compares these features with a reference stored under the claimed identity using a suitable pattern recognition algorithm implemented on a minicomputer. This reference can be reduced in storage size per speaker such that magnetic identity cards can be used as memory to be carried around by the user. Thus the number of users is not limited by the system and no large memory is required in the minicomputer. The results of first experiments are reported.

Optimum properties of particle inertial impactors for a two-dimensional ideal fluid are derived using conformal mapping techniques and improved numerical methods. Results of sequential calculations of one-dimensional contour integrals are matched with analytical expressions for fluid properties near the stagnation point. Particle trajectories are numerically simulated for a range of jet-to-plate spacings and fluid deflecting plate angles. These results are compared with the calculations of Davies and Aylward for a deflecting plate angle beta =90 degrees . It is found that an unconventional angle beta not=90 degrees exists for a given jet-to-plate spacing which maximises the slope of the particle efficiency curves. Although the conclusions are derived for an ideal fluid (Re= infinity ), similar results should apply for impactors operating at finite Reynolds numbers.

The time variation of the deflection of a narrow probe laser beam which is traversed by the shock wave is compared with the theoretical deflection for a model refractive index profile obtained by computer ray tracing. The technique has been applied to the measurement of the pressure in a shock wave generated by the impact of a focused carbon dioxide laser pulse on a water surface. The spatial resolution of the technique is controlled by the diffraction limits of the probe laser beam. In experiments on a 1 mm radius shock wave, peak refractive index changes of 0.2%, corresponding to a pressure of 1.84*10⁷ Pa, have been recorded. The derived acoustic energy in the shock is 13 mu J.

The response of non-cylindrical hot-film anemometers to electric sine waves is analysed according to the Bellhouse-Schulz model and the results are related to the anemometer response to sinusoidal velocity and ambient temperature fluctuations.

An instrument is described which has been designed and fabricated to measure the coercivity, retentivity and saturation magnetisation of cylindrical samples of conducting soft magnetic materials at power frequencies of 50 Hz. These measurements can be carried out even for very thin wires having diameters of about 0.1 mm. The demagnetisation factor and ratio of the sample and pick-up cross-sectional areas are used as parameters, whereas the effects of eddy currents are taken into account geometrically. The tests show that the three magnetic quantities determined with this arrangement are reproducible to within 3%. The possibility of adapting the arrangement for temperature dependence and phase transition studies is also discussed. The instrument is also capable of detecting the presence of different magnetic phases in the sample, whose number has been confirmed through Mossbauer spectroscopy in some typical cases.

An image-moire method using a simple experimental set-up is suggested to determine refractive indices of transparent materials accurate to five parts in the third decimal place.

The electrostatic field distribution established between two coaxial cones is determined numerically. The dispersing and focusing properties and angular aberration terms of this electrostatic velocity analysing field distribution are calculated and expressed in a general analyser equation. The properties of this new analyser are compared with those of the parallel plate and hemispherical analysers.

For pt.I see ibid., vol.13, no.1, p.114 (1980). Describes the construction of an electron electrostatic analyser using the electric field configuration established between two cones maintained at different potentials. The calculated operational characteristics of the electron spectrometer are confirmed by measuring the differential cross section for elastic scattering of electrons from argon atoms at 50 eV incident energy and by observing the helium resonance at 19.34 eV at scattering angles of 23, 60 and 90 degrees .