Table of contents

The article begins by pointing out the requirements placed on the dynamics of measurement due to advanced computing techniques and automation engineering. This is followed by a survey of basic terms such as root mean square deviation and other error definitions, their correlations and interpretations with the aid of modern geometry in Euclidean and non-Euclidean spaces. Relations between data storage and measuring errors are shown by use of the findings of the information theory. Furthermore, methods for the analysis and synthesis, i.e. optimisation of measuring systems are discussed.

Reviews methods for obtaining pressures up to 30 GPa, now that the temperature range in which physical properties can be measured under high pressure has been extended down to 0.03K.

A spectrophotometer system for absorption and reflection measurements between 6 and 10 eV is described. The easily producible hydrogen DC discharge spectrum consisting of a many-line part and a continuum is used as the light source. It is processed by simple electronics to produce the wanted signal. A light guide with quartz fibres gives the reference signal. Measurement temperatures, between 4 and 450K are possible if an appropriate cryostat of double-Dewar construction is used.

A Krytron, triggered by focusing the output from a mode-locked Nd:YAG oscillator on to its grid, is used to discharge a Blumlein into a Pockels cell switch to isolate a single pulse from a mode-locked train.

A high-impedance, high-Q probe for measuring the electric fields present in a plasma is described. This probe can be used for the absolute calibration of wave amplitude measurements.

A double-discharge, Pyrex waveguide laser has been built in order to perform infrared spectroscopy studies in the region of lambda =10 mu m. This simple device provides at least 60 laser emission lines with widths from about 200 to about 700 MHz with a typical power output of 150 mW on each of two beams from an angled coupler on the P₂₀ line of the lambda =10.6 mu m band.

By the use of two microphones in antiphase as transducers, the signal from the sound caused by wind flowing through a tube was separated from the signal caused by the turbulent pressure fluctuations. The turbulence signal was found to provide a satisfactory measure of the wind in which the tube was placed.

A pulse generator is described for the production of calibrated electrical pulses of rectangular shape, with currents selected between 0 and 40 A and durations between 500 and 0.7 ms. Combination of this generator with a suitable integrating voltmeter permits accurate measurements of various electrical properties of conductors even of very low resistivities of the order 10^-8 Omega m, such as synthetic metals based on graphite.

An electrometer was designed to measure absolute currents in the range 10^-9 to 10^-5 A to an accuracy of better than 1.0% of setting plus 0.02% of full scale, and to monitor current deviations down to 0.02% over periods of several hours at constant temperature. Auto-zeroing was included in the circuitry to improve stability and to facilitate use of the electrometer. The electrometer is intended particularly to monitor the stability of the beam current in analytical electron beam instruments. Circuit diagrams are presented together with details on the principle of operation, construction, setting up of the electrometer and performance tests.

A digital electronic system is described which drives a piezoelectrically scanned Fabry-Perot interferometer. The basis of this system is a voltage ramp generated by a digital-to-analogue converter (DAC). A correction to compensate for the nonlinear characteristics of the piezoelectric ceramics is given. Use is made of the digital nature of the ramp to perform several functions useful in modern Brillouin scattering. These are: protection of the detector against the high light levels experienced in multipassed interferometry, ability to change scanning speed before and during data collection, protecting acquired data against laser 'mode-hopping' and the scanning of two Fabry-Perot interferometers in series.

Describes a gamma-ray thermometer and strain gauge which can be used to make measurements remotely. Laboratory calibrations indicate that temperatures can be measured with +or-1K precision over a linear range of 80K, and strains with a precision of +or-14*10^-6 over a range of 2*10^-3. A system capable of measuring vibrating strain with about the same precision is also described. Possible improvements are discussed.

The discharge pulse rates at different magnitude levels are often used as criteria for monitoring the partial-discharge aging of insulation systems. Use of suggested corrections for errors in cumulative probability counting leads to better use of available counters.

The analysis of the desirable features of a vibrating-capacitor probe for adsorption studies and the disturbing effects which hinder their realisation has led to the construction of a set-up which combines low noise and drift, good reproducibility even after movement of the sample, and a low time constant. It is particularly suited for kinetic measurements in adsorption studies for which it is practical to provide direct differentiation of the output; it can also be used for accurate measurements of absolute contact potential differences.

Linear birefringence and linear dichroism are a result of preferential orientation of non-spherical molecules or colloidal particles in liquids or dispersions. A novel apparatus is described for measuring simultaneously the birefringence and dichroism induced in liquids or colloidal dispersions by a magnetic field. The apparatus uses phase modulation and a phase-sensitive detector, the modulator being a phase plate rotated at a steady speed in the light path. Theory shows that a birefringent dichroic dispersion produces in-quadrature photovoltaic signals as measured by the photocurrent of a photomultiplier. These signals are separately measurable using phase-sensitive detection. Results are given for the nominally transparent liquid benzene and several dilute but turbid, colloidal, mineral aqueous dispersions. The latter show clearly the existence of both permanent and anisotropic induced magnetic moments in the colloidal particles, with complete particle alignment being reached at magnetic fields of about 1 T.

By use of an air bearing a spinning-plate magnetometer has been made in which the rotor can run virtually indefinitely without wear and at very constant speed. The voltage output of the probe is proportional to magnetic field strength over six orders of magnitude and can measure steady or slowly varying fields from about 10^-2 T down to less than 10^-8 T.

An instrument using a resonator-terminated acoustic transmission line has been developed for absolute internal friction measurements in the 10 kHz-1 MHz range. It can be used for material studies at temperatures of up to 2000 degrees C and, in the form of a robust probe, for industrial monitoring.

By observing the change in amplitude of a spin echo caused by the motion of nuclear spins in a magnetic field gradient fluid velocities in convective and pressure-driven flow have been measured. In these experiments the smallest velocity detected was 10 mu m s^-1.

A molecular beam epitaxy (MBE) apparatus is described in which some improvements over earlier systems have been achieved. An isolation valve permits the introduction of samples without disturbing the ultra-high vacuum system. The beam fluxes are controlled by a quadrupole mass spectrometer; by this means beams of gallium and arsenic can be kept constant to within 1 and 3% respectively.

A spectrometer, based on interference filters and capable of examining a varying light source, is described; it is designed to scan the wavelength range 340-640 nm in 125 ms. The information is stored over successive scans and an integrated spectrum is obtained, corrected for the variation of response of the instrument. The spectrometer has sufficient sensitivity for use with weak thermoluminescence (TL) emission; the TL spectrum recorded from the 160 degrees C peak of a 5 mg sample of CaSO₄:Mn that had received a dose of 10^-2 J kg^-1 gave a signal-to-noise ratio of 90:1. Examples of the use of the instrument in the application of TL to archaeological dating, where such measurements have not prev iously been possible, are presented.

Equipment is described in which cleaving processing and experimental measurements on alkali halide crystals can be carried out in UHV, all adjustments being made by remote control outside the vacuum chamber. This equipment has been used for measurement of surface charge and potential by the Kelvin vibrating-electrode method, and is described as such, but it is capable of modification for general-purpose, remote-control experiments.

A waveguide system is described which enables the complex permittivity of medium- and high-loss liquids to be measured at 70 GHz. The design and constructional details of two waveguide cells are given together with a brief description of the methods of analysing the data. Results of measurements on various liquids are included.

An intense neutron pulse with a wide frequency spectrum was required for pulse propagation experiments. The neutron beam emanating from the thermal column of the Universities Research Reactor (URR) was modulated by an improved rotary chopper of 86 cm diameter, operating at 2000 rev min^-1 and containing boron and cadmium absorbers. The cross-sectional area of the pulsed beam was 26 cm². The pulses has a 3 dB cut-off frequency of about 1000 Hz and a signal-to-background ratio of about 400.

A circuit is described which provides a simple power supply for ionising and running 125 W high-pressure mercury-argon arc discharge lamps (e.g. type MBL/U) on stabilised direct current. An improvement of 10-20 dB, at 300 mu m, in the total noise of an infrared interferometer is reported, relative to AC operation. The reasons for the improvement are examined.

A simple, smooth diaphragm drive for scanning Michelson interferometers in the visible spectral region has been developed and tested in two different systems.

Describes the methods used to prepare uncontaminated PbTe films on mica substrates by molecular beam deposition from a single source boat and the techniques used to make in situ electrical measurements on the films down to 100K. The as-grown carrier concentration was found to be determined by source conditions and controllable n-type carrier concentrations between 10²² and 5*10²⁴ m^-3 could be obtained. Measurements on films having the lowest carrier concentration indicated that they contained a low residual doping level (<10²¹ m^-3). Room-temperature Hall mobilities improved as the runs progressed and a maximum value of 0.195 m² V^-1 s^-1 was obtained. Films with carrier concentrations greater than 5*10²³ m^-3 had field effect mobilities of approximately 0.08 m² V^-1 s^-1. Exposure of the films to low pressures of oxygen after growth enabled the n-type doping to be reduced to any level down to intrinsic carrier concentrations.

The basis of an improved operation condition for combined electron microscopy and electron energy analysis is outlined. A 30% improvement in accuracy of measurement of point-to-point differences in composition is achieved.

Techniques are described for obtaining simultaneous spatial and spectral resolution of X-rays emitted by high-temperature plasmas formed when fine wires are exploded. Good spatial and moderate spectral resolutions are obtained with a pinhole camera containing multiple films. Small pinches emitting predominantly soft radiation and larger 'flare' regions emitting harder radiation were found with this technique. Intermediate spatial and good spectral resolution results from the use of crystal spectrographs in various geometries. Such combinations show that the pinches have high temperatures (up to 2 keV) while the flares are about one-tenth as hot. Examples of data taken from tungsten exploded-wire plasmas are given for each arrangement. The spatially resolving spectrographs described are also applicable to the study of other X-ray sources.