Table of contents

The basic principles are briefly explained, showing how cross correlation can be used to identify dynamic characteristics of a wide range of telecommunication, structural and process systems. The main emphasis of the paper is on cross correlation flowmeters, which are developing to a stage where they can successfully solve industrial and environmental measurement problems, ranging from the flow of highly polluted liquids in pipes to the flow of gas from volcanic jets. Cross correlation flowmeters are based on measuring the transit time of a tagging signal (turbulence, clumps of particles, etc.) in the flow between two axially separated sensors. The transit time is measured by a cross correlator. The design of the various subsystems is discussed in some detail and the various sensing techniques required for specific applications are described. Cross correlation flowmeters have become a realistic proposition because of the reducing cost of large scale integrated circuits and microprocessors from which the correlator may be realised, a number of different designs of cross correlator are described and their relative merits discussed.

A technique for determining the optical density to relative exposure calibration, or so-called characteristic curve, for photographic emulsions in the extreme ultra-violet (XUV) using a grazing incidence spectrograph and an XUV source of unknown emission is discussed. The authors use aluminium foils of measured thickness and hence known attenuation to the XUV radiation to produce different relative exposures of spectral lines in a spectrograph with a laser-produced plasma as the XUV source. From the corresponding optical densities of spectral lines resulting on the photographic emulsion used in the spectrograph, the optical density to relative exposure calibration for the emulsion is determined. The relative exposures for different spectral lines are related in order to build-up comprehensive characteristic curves using a novel least-squares fitting technique. Characteristic curves for Kodak-Pathe SC5 and SC7 emulsions determined for wavelengths approximately 30 AA using the method are presented.

When using white light double-beam interference microscopes for the identification of interference order, chromatic effects in the optical system can often cause difficulty in the interpretation of the white light fringes, particularly for high interference orders. This problem is discussed and a simple technique to overcome it is described.

A technique is described for sizing and counting aerosol particles based upon the acoustic signal produced by a particle entrained in a circular orifice flow. A model of the process was found to accurately predict diameters of spherical particles in the experimental range of 25-1500 mu m. A device utilising the described principle is of simple construction and can be reliably calibrated.

A simple tape transport system is described which is used for the collection of short-lived nuclides emerging from a He-jet recoil transport system. It is based on pistons driven by compressed air and is both inexpensive and reliable, and allows accurate and reproducible positioning of the radioactive sources at the counting position.

The work reports a simple device allowing AC conductivity determinations at temperatures as low as 90K and the checking of phase transitions accompanied by a conductivity variation in the range 90-400K. The conductivity Arrhenius plots of RbAg₄I₅, Ag₆I₄WO₄, 4AgI:Ag₂MoO₄ and AgI:Ag₂O.B₂O₃, which are known for their high ionic conductivity at room temperature, are presented as examples for the reliability and usefulness of the device.

A simple but accurate method is presented for the stabilisation and measurement of temperature inside a high pressure vessel up to 500 MPa. This involves special mounting of a Pt resistance thermometer, actually located outside the pressure chamber, but itself completely inside the high pressure region.

A relatively simple and inexpensive system is described which digitises a normal photographic transparency or negative. The system, which is controlled by a microprocessor, uses an oscilloscope as a scanning light source and displays the resulting digitised signal on a small television monitor.

A technique has been developed using a SEM (scanning electron microscope) in an unmodified form for the writing of fine line structures with both alignment and location to +or-0.1 mu m over lengths of hundreds of micrometres. The technique is demonstrated by fabricating small numbers of prototype GaAs MESFETS with gate lengths in the sub-micrometre range.

The technique described has been developed for use with zirconium in a 4 MeV proton beam, but is also applicable to other metallic single crystals or polycrystalline materials. After preliminary thinning to approximately 80 mu m, the specimens are reduced to 65 mu m using 1 mu m passes on a microtome. Finally, chemically polishing is used to remove surface damage, giving specimens of good crystalline perfection for the gauge region with a thickness of 50 mu m (+or-1.5 mu m). Shoulders are attached using a laser welding technique.

A technique and a cuvette for circular dichroism measurements of oriented molecules in a uniaxial system are described, whereby the light beam propagates parallel to the optical axis. Particular care is taken to eliminate linear dichroism and birefringence effects, introduced by the imperfections of the orienting liquid crystal matrix.

A novel method of forming precisely reproducible furnace elements by photolithographic techniques is described. The final furnace element is in sheet form which can be wrapped around an insulating former such as alumina or silica. The artwork can be prepared by computer aided design and as the original design can be dimensionally reduced by optical methods the size of the sheet can be accurately matched to the circumference and length of the supporting tube.

The behaviour characteristics of a commercially available hot-wire anemometer have been examined in the presence of low velocities, lwss than 0.1 m/s for the most part, and in both horizontal and vertical air flows. The orientation of the probe in a horizontal flow has been found to have a definite effect on velocity measurements, and a lower limit to the reliable application of hot-wire anemometry has been evaluated for a particular type of probe. Vertical flow measurements have resulted in the discovery of the magnitude of natural convective velocity, and a possible method for determining the dimensions of the temperature jump distance has been developed indirectly from the description of the shape of the calibration curve.

This paper presents an attempt to link the complex and semi-empirical parameters of longwave holography in a way which allows the reader to survey the total problem and optimise the experimental regime. The individual and composite transfer functions of the CRT and the two-step photographic recording are discussed and examined. Requirements for the electronic amplifier that compensates for the non-linearity of these three components and which allows the linearisation of the entire process are discussed. Dynamic range and linearity test are proposed.

A TEA CO₂ laser has been line narrowed by means of a transversely excited low-pressure gain cell scalable to large apertures. This technique has been developed for enhancing the pumping efficiency of optically pumped lasers at high pump energies and has been successfully applied to the 16 mu m output of CF₄ pumped by the 9R(12) CO₂ line.

An electron spectrometer system is described with some illustrative spectra. The system combines the requirements of scanning Auger microscopy with those of high resolution spectroscopy. The spectrometer is a concentric hemispherical analyser with a four-element input lens and can be operated with a high signal sensitivity, low energy resolution (Ca 7eV window), with 0.1 sr angle or with a high resolution and reduced sensitivity.

A stopped-flow technique employing a mini-computer control arrangement is described for use in electron spin resonance spectroscopy. By observing the time dependence of small segments rather than individual points of a spectrum, complete time-resolved spectra in the range 10 ms to 5 min can be obtained with very efficient use of reagents. An algorithm and a suitable experimental arrangement are described for the application of the technique.

For the interferometric detection of extremely small displacements one of the principal limiting factors can be scattered light, having a certain path difference against the main beam, in combination with the inevitable frequency fluctuations of the light source. This paper presents a method to suppress the effect originating from the co-operation of these two deficiencies. The idea is to blot out the scattered light effect by deliberately phase-modulating the light with appropriate frequency and phase swing. A theoretical treatment is given for the principles of this novel method. The paper discusses possible sources of scattered light in a gravitational wave detector and the application of the method to blot out the effect caused by the scattered light. It furthermore describes a method to measure the different contributions of scattered light and presents first experimental results for their suppression. Suggestions and calculations for further improvements are given.

The construction of a simple, economically attractive, variable-temperature cell which can be adapted to a microhardness tester and its application to the determination of the phase transition points in ferro-electric crystals of Rochelle salt are reported.

A versatile time-resolved multi-channel averager has been built using a microprocessor architecture to provide intelligent data acquisition capability. The averager described provides 1 mu s time resolution, multiple channel widths, automatic background subtraction, and multiple operating modes. A high speed cassette tape system is provided for transporting acquired data to a minicomputer for further analysis, and an automatically scaled CRT display is provided for monitoring data acquisition in real time. Illustrative examples of the use of the instrument for studying pulsed afterglow plasmas are discussed.

A heat loss type of anemometer using a pair of bare transistor chips is described. Response time is a few milliseconds and useful range is 0 to at least 15 m s^-1. Polar response varies +or-10%, necessitating individual calibration at a specific orientation. The instrument is battery operated with a total power consumption of 60 mW. Reproducibility of reading is within +or-1% of windspeed 3 to 15 m s^-1.

The application to microcircuits of the electrooptic effects in nematic liquid crystals-normally employed in visual displays-has been investigated using special test structures and active devices. Two electro-optic phenomena have been observed, and the sensitivity to surface potentials and fields estimated. The functioning of both low-voltage bipolar and higher-voltage MOS microcircuits having overglazed dice has been examined qualitatively, but only with AC or pulsed operation at audio frequencies governed by the voltages present. The technique requires a little acquired skill, and simple equipment.

A simple ion gun, which efficiently operates at the pressure range from 13.33-1.33 mPa (10^-4 to 10^-5 Torr) and in the energy range from 250 to 1000 eV, has been devised for ion scattering spectroscopy applications. Mass analyses show that when the source is operated with 99.99% grade gases (Ar, Ne and He) the ratio of the doubly-charged ion to the singly-charged one for Ne and Ar is 0.02 and 0.16, respectively, and the amount of other impurities which consist of CO⁺ and H₂O⁺ is about 2% of the total ions. Intensity curves of singly-charged ions in each case have a broad maximum at the pressure around 53.32 mPa (4*10^-4 Torr). The energy spread is found to be 0.99 eV for He⁺ ion beam by extrapolation to zero beam energy. An application to ISS study is also presented.

Using a combination of a curved crystal analyser and a position sensitive detector the authors demonstrate how an energy resolution of a few eV in the energy range of 10 keV can be achieved without suffering a prohibitive loss in the observed intensity. An experimental set-up is described in which spectra from Raman, Compton and plasmon scattering can be collected in a matter of hours using monochromatic CuK alpha ₁ radiation from a 1.0 kW X-ray generator. After scattering in either a Be or a graphite target, the X-rays were reflected from the (333) planes of a curved Ge crystal and brought to a focus on a position sensitive proportional counter. The measurements on pyrolitic graphite confirm earlier reports of a striking anisotropy in the spectral distribution of the scattered X-rays, depending upon the direction of the experimental scattering vector relative to the basal planes in this layered crystal. The anisotropy arises from the strong directional dependence of the cross section for plasmon excitation in graphite. Some straightforward improvements to the present apparatus would lead to an increase in the observed intensity by a factor of 40 or more.

An apparatus for measuring the paramagnetic susceptibility of molecular oxygen in the vicinity of the critical point of the gas-liquid phase transition is described. It comprises an electronically compensated mutual inductance bridge, a non-metallic gas cryostat and a pressure cell. This cell consists of a measuring part within the cryostat and a spacially separated regulating part outside. The temperature of the sample can be kept constant within +or-10^-3K for several hours in the range of between 150K and 200K. The pressure can be regulated up to 6 MPa with an accuracy of 2*10^-2 MPa. An amount of volume susceptibility change of 1*10^-5 (SI units) can be detected.

In order to make simultaneous and continuous measurements of three kinds of environmental air pollutants, SO₂, NO and NO₂, with a high sensitivity and stability, a wavelength-modulated derivative spectrometer is used. The construction of the optical system, wavelength-modulator, the multi-pass cell of the spectrometer, and the performance are investigated. The limits of identification for each measuring object are: 15 PPB for SO₂, 13 PPB for NO, and 8 PPB for NO₂; for instantaneous measurement, the values are consistent with those calculated. For the measurement of the integrated value over one hour, the limits of identification are: 5 PPB for SO₂, 3 PPB for NO, and 4 PPB for NO₂. Tight correlations are observed between data obtained by the spectrometer and by two other analysers which are based on the flame-photometric detection, and the chemiluminescence method.

A simple ultrasonic pulse cell with reduced variable pathlength for millilitre liquid samples (frequency range about 15-155 MHz) is described. The liquid cavity made from stainless steel has PTFE seals and gaskets and is resistant against many liquids. Attenuation and velocity measurements have been performed for H₂O, CH₃OH, C₂H₅OH and C₂H₅OC₂H₅ at 25 degrees C. The measurements, using a quartz effective diameter of 9 mm and pathlengths from 7-21 mm, show that diffraction correction terms are apparently not necessary.

A simple attachment to the Weisenberg camera for aligning largely mis-set crystals is described. The attachment can be fabricated in any laboratory workshop. The present method can be used to align a crystal (within about 2 degrees ) in which the misalignment in each arc is large (e.g., 10 degrees -15 degrees ). The theoretical formulae needed to evaluate the corrections to goniometer arcs are also derived. Corrections to both the arcs can be obtained from the measurements made on a single photograph.

Describes a Pyrex waveguide carbon dioxide laser operating at a maximum single line power of about 10 W. Although construction is straightforward, excellent single mode purity is achieved in a far simpler way than most conventional systems.

A simple digital type quartz crystal thickness monitor with high sensitivity and good resolution has been designed and fabricated. In the same design another method using the phase-locked loop technique has been provided for the measurement of thickness of the films which can be compared with the value obtained by the digital frequency counter. Both these methods can simultaneously be used for the accurate measurement of the rate of deposition and the total thickness of the films.

For diffractometer studies of crystalline materials scattering from the furnace or cryostat may be superimposed on the sample scattering. For single crystal studies this does not often present a significant problem, because peaks in the background scattering pattern are usually much broader than the single crystal Bragg peaks, and so subtraction of the background is straightforward. However, with powder specimens it is common to have a diffraction pattern composed of comparable intensity and width peaks from both sample and furnace or cryostat. Frequently, cryostat and furnace designs fail to make use of the fact that if furnace shrouds, cryostat tails, and the like have appropriate radii, then scattering from them will not enter the detector. Certainly in some cases this is impossible to achieve because of the nature of the device required. However, particularly for neutron powder diffractometers where relatively large dimensions are involved, it is possible under many circumstances to avoid detection of much of the furnace/cryostat background scattering. The essential problem of concern is: What is the critical radius of a cylindrical tube, coaxial with a powder diffractometer sample, such that no scattering from the cylindrical tube enters the detector?.

The author of the book 'Flowmeters' (Macmillan, 1979) replies to criticism of 'incorrect or misleading statements' which allegedly appeared in his original work.