Table of contents

A simple and inexpensive local enclosure to prevent access to a useful X-ray beam during camera use is described. The design can be adapted for use with any precession camera.

Various types of interfering signals are outlined and measures which can be adapted in order to suppress their effects are described. It is shown that by balancing the whole system including the signal source, the leads and the instrument, as well as twisting and correct screening of signal leads, the susceptibility to external electric, magnetic or electromagnetic fields and coupling to interfering sources can be substantially reduced. A crucial question is finding and constructing a design which avoids ground loops. They are a serious problem in a measuring system. For optimum efficiency, the user of an instrument should take care in matching his arrangement of sensors, leads, instrument and grounding with the design concept of reducing interference susceptibility.

A simple and versatile DC current-regulated power supply that reduces power dissipation across the series pass element by means of a preregulator using thyristors is described. This reduces the total number of power transistors to be used and thereby improves the performance and reliability. The power supply is developed for energising the quadrupole magnet of the focusing system of an electrostatic accelerator. Some of the results obtained during performance testing of the power supply are also presented.

A method is described for the determination of relative efficiencies of an M-306 Bendix multiplier for neutrals and ions. In these measurements, helium ions and neutrals having energies 2-5 keV are used; the beam of neutral particles is obtained by a charge transfer technique. The relative efficiency of the Bendix multiplier for the neutrals with respect to the ions is determined by measuring the neutral and ion pulse rates, while the absolute efficiency is determined from the measurements of ion pulse rate with a Daly detector. The Bendix multiplier appears to have lower efficiency for the neutrals.

The time behaviour of the gas density of an intense pulsed molecular beam is analysed by absorbing room-temperature black-body radiation. This analysis is simpler than the normal method, which consists of absorbing tunable radiation.

A circuit is described that stabilises the centre frequency of a frequency-modulated synthesiser in the VHF-UHF bands. It has been designed especially for high index modulation as used for instance in NMR on oriented nuclei. The circuit improves the long-term stability of the centre frequency by a factor of 100.

With conventional prism beam steering devices, the beam deviation is usually related to the prism movements in a very nonlinear way. Also, the sensitivity is fixed by the wedge angles of the prisms. A new type of device is described with a more linear response than the old types. It has very high resolution which can be varied over several orders of magnitude using the same optical and mechanical components.

A simple inexpensive carbon dioxide waveguide laser with fixed alignment obtained in the construction stage is described. The alignment was still maintained over a two and a half year period. Output power of 1.5 W was obtained routinely with a mixture 3:1:0.5 for helium-carbon dioxide-nitrogen in a 150 mm length laser structure.

Doped potassium bromide discs containing approximately 1% of tetramethyl ammonium halides or metal chromates are shown to be useful as band-stop absorption filters for use with CO₂ lasers.

A simple method of glass protection against the darkening caused by sodium vapour by the use of a Na₂B₄O₇ layer is described. The coating effectively limits the rate of the darkening of glass in temperatures up to 650K.

The construction and operation of a high-temperature oven, particularly designed for use in conventional vibrating sample magnetometers (VSM), is described. The oven may be used in the temperature range 300-1150K. The location of the temperature sensor enables a fast and accurate measurement of the sample temperature. The oven can be heated from room temperature to 1050K in less than fifteen minutes with a temperature difference between temperature sensor and sample of less than one kelvin at the final temperature. The fast cooling rate of the oven permits a quick interchange of samples.

An oven system has been developed which can maintain the temperature of a specimen to an accuracy of <0.1 degrees C in the range of 20-400 degrees C, over time periods in excess of 24 hours, without being affected by room temperature changes of up to 10 degrees C. Entry and exit ports are provided to enable the sample to be irradiated by laser irradiation.

A dilatometer specially designed for a study of the sintering of silicon nitride is described. Densification kinetics could be measured at temperatures up to 2300K. Thermodynamic considerations dictated that the specimens be maintained in a N₂ gas pressure of up to 2 MPa. Hot-pressed boron nitride was the only material found suitable for the high-temperature parts of the dilatometer. The pressure vessels contained an RF furnace with graphite susceptor thermally insulated with zirconia granules and housed in a vitreous silica tube. This simple arrangement allowed high heating rates and a minimum of maintenance. The dilatometer is readily adaptable to high-temperature properties measurements where inert gas overpressures are desirable.

A micrometer drive with >20 mm of travel, stepper motor drive and resolution of the order of 1 mu m is described. While commercial units are available with similar specifications, they generally cost $1500 or more. The unit described is very simple, consisting of a commercial, good-quality nonrotating micrometer head, a high-resolution stepper motor, a frame and an electronic drive card. It can be made easily for under $100 (1983 prices). Backlash and nonlinearity are small.

There is no need to determine the high-voltage characteristics of high-voltage insulation systems used in high-powered electrical machines in order to evaluate the relevance of 0.1 Hz measurements to those taken at power frequency and to investigate their value for diagnostic purposes. A computer-controlled system for the generation of test voltages and the measurement of loss tangent and capacitance in the range 1 mHz to 1 kHz and 100 V to 22 kV RMS is described. The high voltage generator is basically a class B amplifier with an output rating of 30 kV (peak) and 100 mA (peak). The measurement system is based on the analysis of the out-of-balance signal of a modified capacitance bridge. The accuracy of the system is discussed and measurements from samples of high-voltage conductor bar insulation used in turbo-generators are presented.

The authors describe the successful development of a variable-frequency test generator suitable for testing rotating electrical plant with voltages up to 31 kV (peak) (22 kV RMS) over a frequency range DC to 1 kHz subject to the current limit of 100 mA (peak). The design, which is based on a high-voltage class A/B amplifier in a totem-pole configuration with nonlinear control, uses a fibre optic system to provide electrical isolation and is capable of supplying a range of waveforms subject only to rating limitation. This makes the generator a valuable research tool permitting many types of investigation including the effect of distortion on measurements obtained from the standard 0.1 Hz generators.

A circuit suited to inelastic electron tunnelling spectroscopy is described in detail. It combines resonant tuning with some high-impedance elements. It has proved to be robust against stray pick-up yet also to give a good signal-to-noise performance. A high-frequency, 100 kHz, version of the circuit is shown to be better than 10 kHz or 1 kHz equivalents. The quality of the spectra is not significantly degraded when the circuit is interfaced to a desktop-computer-controlled data acquisition system.

Coated ceramic electrodes for establishing the uniform electric fields in the reactor and drift regions of an ion mobility spectrometer (IMS) or plasma chromatograph (PC) are described. Spectral results for ceramic and conventional stacked metal ring constructions are presented and compared with theory.

From the measured magnetic field distributions at constant excitation, the objective focal properties for two experimental single pole piece electron lenses of equal dimensions, one with a spherical pole and the other with a cylindrical pole are computed at different diameters of the axial bore in the pole piece. The electron optical properties of the two objective lenses including their spherical and chromatic aberration coefficients are compared. The effect of the pole piece shape, its axial bore size and its orientation with respect to the incoming electron beam on the objective focal properties are discussed in detail. The results should be useful in the design and operation of single pole piece objective lenses for the transmission and scanning transmission electron microscope.

Semiconductor preionisation of CO₂ TEA laser discharges has enabled sealed lives of up to 2*10⁷ pulses to be achieved with the high CO₂ concentrations ( approximately 50%) needed for maximum peak power output per unit discharge volume. Operation was at pulse repetition frequencies up to 100 Hz and O₂ levels were kept below 0.3% using unheated tin oxide-precious metal catalysts.

An optical method is described which allows a phase measurement to determine the thickness of thin films with rough surfaces. It uses a Michelson interferometer modified to include a specimen with the laser beam grazingly incident on the surface of this specimen. The resolving power is typically a few hundred nanometres, which corresponds to the diameter of 'microcrystals' usually found in the layers of special interest here (layers similar to 'Electrofax'). The method described can be used generally and also for smooth-surfaced films which are transparent to the measuring light but which have opaque microcrystals embedded in their bulk.

The trend for electronic devices and systems to become smaller has led to an increased interest in the problems associated with the miniaturisation of mechanical objects. Because of this miniaturisation certain errors become important and an attempt is made to evaluate the nature and extent of these errors for a very simple geometric feature of engineering components.

A brief review of the sensor systems used in seam tracking for arc welding robots is represented. The authors present a new approach to the problem which makes use of the welding arc as the light source to illuminate the weld seam. Single-line images perpendicular to the direction of movement of the arc gun are analysed for grey-level distribution. Various forms of data processing are assessed as a means of extracting the seam position. Averaging, cross correlation and matched filtering are shown to be equivalent for the special case of butt welds. It is shown that the seam position can be extracted from groups of single-line images using these different filtering techniques.

The construction and operation of the transducer and its associated pickup and circuitry is described. Calibration data are presented and discussed. Features of the transducer are its small size, lack of slip-rings or internal electronic circuitry and the ability to interchange flexures to set the full-scale torque of the device.

An apparatus for isothermal annealing and study of crystallisation temperatures and activation energies in amorphous semiconductors is described. The temperature treatment is performed in a high-vacuum chamber with an ambient argon gas maintained during the annealing time. When studying the crystallisation process, the semiconductor conductance is measured by means of the constant voltage method. An x-t recorder then monitors the variation in the semiconductor conductance. An electric line controller facilitates automatic turn off of the process. If desired, fast cooling of the sample holder is possible by means of tap water. Samples of amorphous ZnTe have been crystallised. The activation energy obtained was 2.8 eV and the room-temperature time for onset of crystallisation was found to be approximately 5*10¹⁸ years.

The sensitivity of a Gardon-type sensor for convective heat flux measurements has been estimated analytically assuming uniform heat transfer coefficient over the foil surface. The linear range is characterised by a constant sensitivity factor of 0.25, and is attained, irrespective of sensor dimensions or environment, so long as the Biot number is less than 0.16. Calibration experiments have been performed on a heated aluminium sphere using four sensors of radius to thickness ratio 13.3 to 33.2 with foil thicknesses 0.05 and 0.075 mm. The sensor, essentially a constantan foil mounted on a copper tube, works as a differential thermocouple. Addition of a constantan wire to the copper base further enables measurement of local temperature.

Platinum resistance thermometers are widely used in temperature measurements not only for calibration purposes but also in industrial applications. A new automatic instrument is described which can determine the actual value of the resistance of a platinum resistance thermometer in less than 0.52 s with a resolution of 8 PPM. The self-heating index can also be determined and the instrument is able to multiplex up to eight different platinum resistances. The temperature is calculated by using the interpolation formulae defined by the International Practical Temperature Scale of 1968 (IPTS-68).

A correlation method is described for analysis of electrical impedances. The impedance is investigated as part of a four-terminal network, allowing general system analysis techniques to be applied. With a pseudorandom noise signal as input the measured cross-correlation function corresponds, under certain conditions, to the impulse response of the four-terminal network and contains the information about the network components via the time constants of the four-terminal network. The method has been applied to electrical two-terminal networks and to a liquid capacitor filled with a solution of poly- gamma -benzyl-L-glutamate in 1,2-dichloroethane. The latter application demonstrates that information on the dynamic behaviour of a chemical system and its changes with time can be obtained directly.

Techniques of absolute and differential helium pycnometry combining good sensitivity with simplicity of experimental equipment and procedure are described. These techniques are suitable for measuring the density of (or the adsorbability of He in) powdered or porous solids. Their application is illustrated on pellets prepared by compaction of finely powdered ('colloidal') graphite.

The authors deal with flowmeters based on the measure of the vortex-shedding frequencies of the flow product behind an obstacle immersed in the flow. This measurement is very precise when it is carried out by counting the impulses exercised by the vortices on a flat plate placed in the wake of the obstacle. One can then define a constant Strouhal number, independent of the degree of obstruction of the fluid vein d/D, the obstacle angle theta and the water velocity. The overall performance of the device in both permanent and nonpermanent flow regimes is studied; the instrument functions as a digital measuring device.

This communication describes a method of referencing out adventitious intensity variations in an optical fibre intensity-modulated sensor by measuring the transmitted light intensity at two wavelengths, one of which carries the signal information and the other being used to normalise the intensity.