Table of contents

Instrumentation associated with large boilers is reviewed, particular emphasis being given to new work reported at a recent conference. Research, testing and operational functions are all covered. Some particularly novel instruments described are aimed at monitoring pulverised fuel flow and particle size, water level, the carbon content of ash and the percentage of voids in a two-phase mixture. Other measurements discussed include the following: coal level; flue gas analysis; water purity and corrosivity; steam, water and air leaks, and water flow.

The determination of fluid flow velocities with conventional equipment is sometimes impossible owing to extreme environmental conditions or unacceptable disturbance of the flow pattern and increase in flow resistance. Transit time analysis of fluctuations in water temperature, pressure, radioactivity, etc., using suitable detecting elements can then still often be applied. In the downcomer region of the reactor system of the 50 MWe Dodewaard boiling water reactor with natural circulation, 30 pairs of fast response thermocouples are used to detect temperature fluctuations in the turbulent flowing water. After amplification and filtering, the signals of each thermocouple pair are fed into a multipoint polarity coincidence correlator to form the cross correlation function C₁₂ (kΔτ). From this function the mean transit time τ₁ of the temperature fluctuations to cover the distance l between the thermocouples is easily found. Then the local velocity follows from the simple relation V_H2O = 1/τ₁. The applied method has proved very useful in the determination of local fluid velocities in the range 0·15-1·50 m s⁻¹. From these local measurements radial and axial velocity profiles and total recirculation flow can be derived.

The generation of independent random binary digits with an extremely small difference between the probabilities for 0 and 1 is discussed and shown to be practicable by means of a scale-of-2 counter counting randomly timed input pulses for a fixed time interval. It is shown that such digits can be used to form other random numbers with appreciable advantages of speed and accuracy, in comparison with the direct generation of similar numbers by means of a scale-of-n counter, where n>4. The use of ternary digits, generated with a scale-of-3 counter, would give a slight further theoretical advantage, but would be less convenient to implement than binary.

Axial potential distributions in electrostatic slit-aperture lenses, consisting of plane and parallel electrodes, are derived using the method of conformal transformation. An improved iterative scheme is given which, for the first time, enables solutions to be obtained for multi-electrode configurations in which the aperture widths are larger than the electrode separations. No special conditions relating one aperture width to another, or relating one electrode spacing to another, were assumed. As an example, the axial potential distribution in the electron bombardment source used in AEI mass spectrometers was calculated; for this an analogue consisting of five apertured planes and an apertureless plane was used. Electrodes of finite thickness were each represented by two planes of infinitesimal thickness. The same problem required computer time greater by at least a factor of ten when solved by the method of numerical relaxation.

For computer display systems that involve the representation of information in diagrammatic form, the fixed parts of the diagram may be stored on film and optically projected on to the screen of a rear port cathode-ray tube. The variable information is written on the fixed diagram by the electron beam moving under computer control. This arrangement leads to a low cost configuration in terms of computer loading and storage, whilst the display itself may be projected in colour to provide a bright, flicker-free image. For linearized optical and electronic formats the major deficiency is the lack of registration between these two images, and where a large number of film slides need to be changed frequently automatic registration is desirable. This paper describes an opto-electronic servosystem which aligns the electronic format to the optical format for origin errors every time a slide is changed.

A method has been developed to grow sets of thin single crystals with selected orientations from a common seed crystal for infrared spectroscopic investigation. The crystals are grown between NaCl or KBr windows from the melt under accurately controlled temperature conditions.

Monochromating properties of x-ray monochromators can be described completely by the characteristic filter function ψ, for the determination of which it is necessary to know the important physical characteristics of the monochromating unit (the distribution of the emissivity in the focus and the reflection curve of the crystal) and the geometry of the experimental arrangement. The analytical form of this function is given for Johann's monochromators with approximate focusing, and the properties of these monochromators are demonstrated on a series of computations of the transmitted wavelength distribution for lower and higher Bragg angles θ. The general results of computations are summarized in several rules for the choice of parameters of monochromating units.

The reverse breakdown voltage of an avalanche photodiode detector depends on the temperature of the diode. To operate at maximum signal sensitivity the diode must be biased just below this avalanche breakdown voltage. The diode output noise rises sharply at breakdown, so the bias voltage requires critical adjustment to obtain the maximum signal-to-noise ratio. The paper describes how the diode output noise can be used to adjust the applied bias voltage automatically, to compensate for changes in diode temperature.

Numerical ion trajectory calculations in a simplified model of a Daly type conversion detector have been performed to check how the impact point of an ion on the converter depends on the geometry of the conversion chamber, the point of entrance into the detector and the initial energy (0-10 keV) of the considered ion. A relation has been deduced between the initial ion energy and the position of the converter for a central point of impact.

With the chosen model dimensions the converter has to be adjustable over 10 mm, in order to meet this `central impact' condition for ions with initial energies up to 10 keV. Consequently, the influence on the detection efficiency by inhomogeneities in the converter surface, the scintillator material and the cathode of the photomultiplifier has been eliminated.

With the aid of the numerical results a conversion detector has been built with an adjustable converter, suitable for nonsimultaneous detection of 0-10 keV positive ions, and an experimental verification has been carried out. For the chosen configuration a good agreement exists between numerical and experimental results. The calculated ion trajectories therefore describe the real ion motion in the conversion chamber rather well.

A set of accurately known calibration points for He (I) photoelectron spectroscopy is tabulated. The set covers the range of ionization potential from 7·02 to 21·19 eV, or of electron energy from 14·20 to 0·03 eV, at intervals less than 1 eV over most of the range. It is shown, by using these points, that a commercial electrostatic deflection analyser instrument is linear in electron energy at electron energies above 6 eV, but that at lower energy there is a progressively increasing deviation from linearity.

Mechanical alignment errors in a vacuum ultraviolet scanning reflectometer using a planar reflecting specimen are briefly discussed. A reflectometer is described which possesses the degrees of freedom necessary to eliminate mechanical alignment errors. Estimates are given of the size of the alignment errors which remain after visual alignment of the instrument, and it is concluded that the largest residual error results from the inaccuracy in obtaining an absolute value for the angle of incidence.

Mass transfer analogue techniques can provide a quick and inexpensive method of determining convective heat transfer coefficients. One method involves coating the surfaces under investigation with a thin layer of naphthalene and observing the rate of sublimation into an airstream passing over the surfaces. The success of this method is dependent upon the naphthalene coating being of suitable quality and uniform thickness. A spraying technique for applying the naphthalene has been developed and has achieved consistently reliable results for both external and internal surfaces.

The resistance-displacement characteristic of a magnetoresistor moving in a magnetic field is examined. The factors affecting the linearity of the characteristic are studied, and curves are shown which provide design information for sensitive displacement transducers using magnetoresistors and rectangular section pole-pieces.

The stabilization of a device with a negative resistance is described. The device is maintained at constant power by the multiplying unit and servo-system. The power signal is obtained from a Hall effect crystal whose input current depends on the device voltage, and whose magnetic flux depends on the device current. Experimental characteristics obtained using the stabilizer are given.

A high temperature spherical adiabatic calorimeter for the determination of specific heats and enthalpies of transformation of iron alloys in the temperature range 650-1750 K is described. The design criteria and construction of the calorimeter are detailed, and an automatic-programming and data-logging system is outlined. The results of determinations of the enthalpy of the α-γ transformation of iron are reported, and these show the reproducibility and absolute accuracy of the calorimeter and its associated equipment to be ± 1·2% and ± 1·5% respectively for an enthalpy of transformation of 923J per g atom at 1184 K.

A small electron energy analyser has been built. It is a three-electrode retarding-field type electrostatic analyser with an outside diameter of 2·0 mm and a length of 14 mm. It is self-orientating parallel to a dc axial magnetic field, in order to study electron energy distribution function in a beam-plasma system.

A vacuum microbalance system is described in which samples were heated by focused radiation. The heat source was a 1 kW projector lamp and an ellipsoidal mirror. Small specimens of good conductors could be heated rapidly and then continuously weighed at controlled temperatures of up to 1000°C, while the rest of the vacuum system remained cool. Thermomolecular spurious mass effects were no more serious than with conventional heating methods. The apparatus has been used for studies of metal oxidation.

A vacuum cell is described for use in the reference beam of a double beam infrared spectrometer. The cell is so constructed that the light absorbed by a disk of absorbent can be subtracted from the total spectrum of disk and adsorbate by the insertion of either a wedge or a disk of the adsorbent into the reference beam. This, in suitable cases, leaves the spectrum of the adsorbed species without the background spectrum of the absorbent. Typical spectra obtained using the cell are shown.

A miniature furnace suitable for routine collection of x-ray data up to 1000°C from single crystals on the Hilger and Watts linear diffractometer, without restricting the normally allowed region of reciprocal space on the diffractometer, is described. The crystal is heated primarily by radiation from a surrounding current-heated, stationary platinum coil wound on a silica bracket. The coil is split at its middle to provide a 4 mm gap for crystal mounting and x-irradiation. The crystal, mounted on a standard goniometer head, can be rotated and centred freely, as in the room temperature case. There is no need for any radiation shields or water-cooling arrangement. Investigations up to 1500°C are possible with slight modifications of the furnace.

Two alternative designs of a sheet metal adapter are described which make possible rapid loading of cut films into the plate holders provided for use in Siemens Elmiskop electron microscopes.

The design and operation of a conductivity probe for the measurement of concentrations is reported. Consideration is given to the measurement of both constant and fluctuating concentrations, as well as to the probe response time.

A highly stable alignment device using self-aligning bearings coupled with piezoelectric expansion columns has been developed and applied to a Fabry-Perot etalon. The accuracy of alignment was greater than ± 10⁻⁷ rad.

A cryostat for simultaneous measuring of thermal conductivity, electrical resistivity and thermoelectric power of metals and alloys in the presence of low temperature tensile deformation is described.

The detailed way of assembling capacitors for the absolute determination of permittivity of liquids is described. Sources of errors and precautions to be taken are discussed. The following results of measurements of the permittivity of various commercial benzenes (referred to air of about 30% humidity) at 20°C were obtained: Sample I: ₂₀=2·2841 ± 0·0001; sample II: ₂₀=2·2858 ± 0·0002; sample III: ₂₀=2·2857 ± 0·0002; sample IV: ₂₀=2·2879 ± 0·0002. The temperature dependence has been also investigated.

A method is described for the preparation of contacts for electrical measurements on very small samples (several mm²) of ultra-rapidly quenched metastable alloys of iron in aluminium. A new type of sample holder is described which is useful for electrical resistance measurements of these small samples over a wide temperature range. Sample holders are constructed so that they can be stacked for mounting within a cryostat. The materials used enable these holders to withstand temperatures up to and above 700 K.

The design and performance of two powder dispensers for feeding mineral, non-metallic or metallic powders into reactive gaseous environments is described.