Table of contents

Over the last few years, developments in electronics have simplified the design and costs of robot control systems to the point where small-scale robotic devices can be considered for use in the laboratory for the automation of experiments. This review article describes the basic features of small-scale robots and indicates the problems and limitations of current devices. The design of robotic systems and the developments which may be expected are discussed.

A reactor nozzle is described in which the nozzle tip is at the highest temperature of the system.

A re-entrant resonator for in vivo ESR spectroscopy is presented. The sample region is a cylinder 36 mm in diameter and 100 mm in height, the overall dimensions of the resonator are 11*11*5 cm³, where the smallest dimension is along the direction of the external DC field. The resonant frequency is 883 MHz and the unloaded Q_u factor of the empty resonator is 1050; when the cavity is loaded by 49 cm³ of water this value goes down to about 300. Under these conditions it is still possible to couple the cavity to the bridge and to perform ESR experiments.

Deals with a new liquid conductivity measuring system, comprising a novel conductivity cell and an 'in-circuit' resistance measuring arrangement. The conductivity cell is an absolute device in which the conductivity is related to the measured value of conductance and a single length measurement. It does not require calibration with a standard solution. The results obtained with a prototype model are encouraging and support the theory presented.

A digital correlator has been built which calculates the full correlation function of a statistically stationary random signal.

A practical method is described for detecting broken steel cables in flat elastomer belts. Cables are permanently magnetised by a preconditioning technique which results in externally fringing fields at a cable break. These fields are detected using passive monitoring coils above and below the surface of the moving belt. Voltages induced in coils by the motion of the fields are used to analyse the type and extent of failure in these important mechanical handling belts.

Design procedures and examples are given for a room-sized cubic coil system to shield an elongated experimental region which extends from the centre outwards towards a side of the cube. Depending on design specifications, the experimental region can be extended in both directions. For a basic cube of 3*3*3 m³ with an experimental region of 0.4*0.4*1.3 m³, an off-centre uniformity of ( mod B mod _max- mod B mod _min)/( mod B mod _max+ mod B mod _min)<+or-2-3% can be achieved for all three components of the external field. For shorter regions an improved uniformity is possible with different designs.

A diode array spectrometer is described using an entrance slit, a holographic grating and a photodiode array as the only optical elements. The optimised design of these parts leads to a compact instrument (2f=116 mm) with a large aperture (f/2.3) highly suited for spectral measurements on small areas (diameter 0.1 mm) within a few ms. In addition an adequate ceramic-based mechanical set-up, an electronic data processing system and some major applications are discussed.

The performance of a double, chevron-mounted, microchannel plate ion detector of an atom-probe instrument has been studied using 3-25 keV He⁺, Ne⁺ and Ar⁺ ions. Pulse height distributions were recorded and the results indicate that the gain of the detector is strongly dependent on the ion energy. This energy dependence was found to be related to the secondary electron yield in the ion-channel-wall collision. However, the detection efficiency in atom-probe operation need not be affected by variations in mass and energy if an appropriate noise discrimination level is enforced and provided the ion energy exceeds approximately 5 keV.

A wide variety of experiments in semiconductor physics involve the analysis of transient phenomena resulting from the return of a system to electrical equilibrium. The essential data are the amplitude and the time constant of the transient. Deep level transient spectroscopy (DLTS) is a capacitance method for the study of deep impurities and defects in semiconductors. The DLTS apparatus described produces a sampled data record of the entire transient which may be analysed using linear regression by the method of least squares approximation. The system was applied to the investigation of deep traps in gradient freeze grown GaAs.

The authors have designed and developed a wavelength control circuit for fine control of the wavelength of a commercial N₂-laser-pumped dye laser system. Using this they were able to lock the dye laser wavelength to an atomic absorption line for long durations.

Presents a theoretical analysis of a hexapole magnet used for state selection and focusing of the F=1, m_F=0 hyperfine state in hydrogen masers. The analysis determines the relative importance of the magnet properties and the geometry of the beam system in providing state selection and focusing. This in turn shows how the system may be optimised for minimum hydrogen flow at a given level of maser oscillation, thereby improving frequency stability (via reduction of the spin exchange interaction) and increasing operating time for a given volume of hydrogen gas.

Some types of flowmeter are based on the measurement of the frequency of vortex shedding produced behind an obstacle immersed in the flow. One can then define a constant Strouhal number, independent of the degree of obstruction of the fluid vein, the fluid stream, the obstacle angle and the velocity. This result is shown to be valid for an inclined obstacle. Within the range of Reynolds number used (1500-15000, with water) and for a given value of d/D (obstacle height/channel depth), the experiments have shown that the vortex frequency n increases linearly with the flow rate. This result is also valid for air.

The use of light-emitting diodes as dynamic pressure transducers is described. An equation describing the pressure dependence of the forward bias of the light-emitting diodes is derived. The determination of the pressure coefficients of the diodes with a hydrodynamic shock tube is also described. Experimental results for 12 light-emitting diodes are given.

An optical displacement transducer, based on commercially available photodetectors, has been developed. The linearity and frequency response are analysed and the results presented show a useful dynamic range of 500 mu m at a frequency up to 50 kHz. Immunity from gross misalignment is noted. Practical designs are illustrated with an application to amplitude monitoring of ultrasonic transducers.

A VG Scientific HB501 scanning transmission electron microscope has been fitted with a novel system for recording microdiffraction patterns from extremely small volumes of matter (less than 500 atoms) at near-unity detection quantum efficiency and high resolution (0.25 mrad). Electrons are incident upon a 35 mm photographic film which is separated from the ultra-high vacuum of the specimen chamber by a 7.4 mu m thick window of Kapton polyimide foil. Results show that the new system is a considerable improvement on previously available detection techniques.

Optical pulse width modulation has been used to produce two high-frequency electrically isolated analogue data links offering low noise and distortion at modest cost.

The safety of commercial nuclear power plants is of importance to designers, builders and operators of such large and complex plants. The emphasis on safety has led to the requirement for highly reliable fail-safe systems for their control and protection. The authors describe one such system, the individual sub-assembly temperature monitoring system (ISAT) which is being developed for the commercial demonstration fast reactor (CDFR). The system incorporates recent advances in solid-state electronics and in particular microprocessors to implement time-shared data acquisition techniques to obtain and process data from around 1400 fast response thermocouples whilst meeting the required levels for reliability and availability.

In a previous article (Kunski and Vanier 1982, to be referred to as KV) the authors reported the results of measurements of the magnetic shielding characteristics of concentric cylindrical enclosures made of Moly Permalloy, such as are used in hydrogen masers (Kleppner et al 1965, Vanier 1982). The arrangement studied was a system of five shields spaced by 25.4 mm with the outside shield having external dimensions 762 mm length and 305 mm radius. In this comment, the authors report on the characteristics of these shields when used on the maser itself.