Table of contents

From 1948 on Lincoln G. Smith developed mass spectrometers based on time and frequency measurements. With his last machine he obtained an accuracy of the order of 1 to 10⁹. After his untimely death in 1972 his unique instrument was moved to Delft, where its development is carried on.

The pyroelectric effect has been known for many years. However it is only in the last few years that a lot of applications have been found. These occur both in technology (i.e. infrared detection, imaging, thermometry, refrigeration, power conversion, memories, biology, geology, etc....) and science (atomic structure of crystals, anharmonicity of lattice vibrations etc....).

During a recent investigation of electrostriction in yttrium iron garnet it was observed that different experimental configurations and samples produced a variety of spurious effects, which are the subject of this paper. Although somewhat inconclusive the results indicate that measurements of electrostriction require great caution if genuine results are to be obtained.

Many analytical laboratories are now using gas chromatographs with automatic injection systems to increase the instruments working time from about 8 to 24 h a day. All such automatic systems must use a computing integrator to report results from the chromatograms and we have used the Basic programming capability of our integrator to provide a safety system not provided with the instrument.

The new nicrosil-nisil thermocouple combination appears to have much greater stability than the commonly used nickel-chromium, nickel-aluminium (type K) thermocouple. Its general acceptance in industrial applications is hindered in part by the cost of replacing existing instrumentation designed for use with the type K thermocouple. This note points out that some measuring instruments of this type may be modified very simply to work with signals from nicrosil-nisil thermocouples.

Using high order reflections, double-crystal rocking curves less than 0.1 s of arc wide are achieved. To use them for double-crystal topography (Bonse and Kappler 1958, Bonse 1958, 1961) it is necessary to stabilise the operating; point on the flank of the rocking curve against variation Delta theta caused by temperature drifts. An automatic control was developed which maintains the relative orientation of reference crystal and sample about the theta axis constant for exposure times of up to several days with an accuracy of better than 10^-2 s of arc. The controller comprises two stages. Coarse adjustment is accomplished by a stepping motor and fine control by a piezoelectric transducer.

The production and use of a simple electronic amplification system (incorporating an automatic arming facility) for use in shock-speed timing in conjunction with a thin film shock-sensor in a shock tunnel located in an electrically noisy environment is described.

A fully digital phase sensitive detector which utilises a microprocessor card is presented. This unit can replace a sophisticated lock-in amplifier in most applications. The instrument stores the signal in a 1024 channel memory, thus permitting further numerical processing of the data. The programs for data processing can be implemented by the use to suit each particular experimental situation. The noise bandwidth of the instrument has been theoretically evaluated, and compared with that of a conventional phase detector, a degradation of the S/N ratio of 1.6 was obtained. The prototype has been used for the detection of the signal in a wide line NMR spectrometer substantially confirming the theoretical results. The instrument operates from 1 Hz to 32.25 kHz.

An inexpensive and relatively simple correlator based on the principle of measuring the time of arrival of photopulses has been built for application to photon statistics. In this device solid state memories replace the commonly employed multichannel analyser for the purpose of storing the time interval distribution. This cuts the overall cost and makes possible the realisation of a compact, real-time, 256-channel instrument with a resolution time of about 200 ns (using bipolar memories). The growth of the correlation function can be monitored on a common CRT through the use of DACS. Some results concerning the direct measurement of the second order field correlation function for a non-Gaussian light source are reported.

For pt.I see ibid., vol.12, p.1091-9 (1979). An analysis is presented of the errors in total reflection time domain spectroscopy and expressions derived which allow estimates to be calculated for the random errors in the results of each experiment. A simulation method is also described which allows estimates to be made of the level of the unwanted reflection errors. In addition, the aliasing and leakage errors inherent in the use of the discrete Fourier transform are analysed. Although aliasing was found not to be a serious problem in practice, it was concluded that leakage could be if the proper precautions were not taken.

A non-invasive method of monitoring gas flow in pressurised metal pipelines is described. The electrical resistance of a heated section of pipe as a function of gas flow is monitored using low-cost circuitry. The instrument provides accurate timing of pulsed gas flows and may be calibrated to measure flow rate and volume. The system has general applications in monitoring fluid flow in metal pipes of various shapes carrying hazardous and volatile fluids.

A new non-contact and automatic method of measuring surface strain has been developed. It makes use of the speckle displacement that is detected by cross correlating the signals from a photodiode array. According to a theory the difference between the speckle displacements for a pair of symmetrically incident laser beams is proportional to the surface strain parallel to the plane of incidence and independent of the translational and rotational components. This relation is verified by experiments using a metal specimen subject to uniaxial strain that is measured by a resistance gauge. The gauge length of the present method is given by the laser spot size and the sensitivity is of the order of the array pitch divided by sensor distance. They are 1 mm and 20 microstrain, respectively, in the experiments.

A differential heterodyne Mach-Zehnder interferometer using a digital phase tracking scheme is described. The tracking device is a prototype for the new fibre optic hydrophone and is capable of maintaining the interferometer at a maximum sensitivity in the presence of large random drifts up to 200 pi rad s^-1.

A knowledge of accurate data on thermal conductivity of liquids and gases is essential for optimal design of many engineering units. Only a few compounds have been studied and the investigations have been limited to temperatures below the normal boiling points. This paper discusses an improved transient hot-wire technique based on the perturbation of an ideal vertical line source with a ramp in power which signifies: (i) minimal free convection, radiation and Knudsen contributions to the apparent thermal conductivity, (ii) enhanced sensitivity to greater utilisation of the overall resistance change of the wire, and (iii) decreased capital cost relative to previous instruments due to use of a microcomputer. Based on a detailed mathematical model of this technique, an instrument has been designed and constructed. Thermal conductivity measurements on liquid toluene, a proposed standard, have proved the viability of the proposed technique. Results are in excellent agreement with the measurements of other investigators. The precision and accuracy of the results are estimated to be better than 0.8 and 1.1% respectively.

Earlier work on a substitution method for the accurate measurement of the low frequency dielectric constant of a solid has been extended to allow for the effect of stray capacitance. This predicts a simple trend, of the apparent dielectric constant of the solid with the dielectric constant of the substitution liquid, which has been verified experimentally. Applying the method to a sample of pure fused quartz yields a value of 3.80751+or-0.00003 at a frequency of 1592 Hz and a temperature of 25.O degrees C, compared with 3.8073+or-0.0004 using the earlier technique.

A precise two-dimensional positioning device has been developed for use in conjunction with a resonant scattering spectrometer to study the spatial distribution of solar oscillations. The principle of operation and constructional details are discussed and the experimental performance is evaluated by analysing the results obtained from sequentially scanning four quadrants of the solar disc.

A method is presented for obtaining the temporal evolution of the plasma potential, which is assumed to be given by the floating potential of a simple emissive probe. The construction of the probe is also described. The method avoids the slow time response of the usual technique where the floating potential is measured across a high resistance. During each sweep of the probe voltage, the changing of the sign of the probe current, which is sampled at a specific time, gives rise to a negative pulse, driving the pen-lift of an X-Y recorder. Since the real floating potential is measured where the probe current is zero, the disturbance of the plasma is kept as low as possible.

Describes an instrument, the 'vibrating-electrode field meter', which allows sensitive measurement of electrostatic field intensities at temperatures up to 1000 degrees C and at pressures up to 0.6 MPa. The operation of the vibrating-electrode field meter is based on the movement of a conducting electrode in an electrostatic field. The sensitivity ranges from 10 V m^-1 to 30 kV m^-1.

Transmission lines discharged through spark gaps are used for a number of pulsed lasers. This paper analyses the power requirement of a N₂ laser for two modes of operation of spark gap, namely, triggered and untriggered mode. The analysis clearly shows the advantage of using a spark gap triggered at appropriate time.

This paper describes a solar-cell characteristics plotter with its associated sample holder. The plotter has facilities for both manual and auto-plotting with built-in current limit against damage of the solar cell under test. Either current or power output can be plotted as a function of terminal voltage and there is provision for marking the maximum power point on the curve. The sample holder allows the temperature of the solar cell to be varied over a range from approximately -188 to 250 degrees C and permits investigation of other properties of materials used in the making of the solar cell, e.g. the antireflection layer. If temperature variation is not required the holder can be water cooled to prevent overheating of the solar cell during test. The plotter can also be used for the investigation of other semiconductor devices, and is ideal for use in small research and development laboratories.

A very simple CW X-ray source has been constructed for use in laser-plasma experiments to free various X-ray diagnostic alignment procedures from the need for laser shots. It has been used both as a continuum and a K alpha source. A rough guide to the bremsstrahlung and K alpha emission for different target materials and accelerating potentials is given.

A new experimental method has been developed for measuring the kinetics of reaction of metals with oxygen. The apparatus utilises two high temperature electrochemical cells which are controlled by an electronic circuit which maintains a constant partial pressure of oxygen and, at the same time, measures the instantaneous rate of consumption of oxygen during the metal-gas reaction. The cells incorporate a calcia-stabilised zirconia electrolyte. The method was evaluated by measuring the kinetics of reaction of iron with oxygen. The results obtained are in good agreement with previously published results, but the new method is shown to be much more sensitive to transient kinetic effects.

For most purposes the requirements for an ideal ultrasonic probe are high efficiency, compact pulse shape and reproducibility in construction. For many practical applications the requirements of high efficiency (giving good signal-to-noise ratio) are paramount and the other ideals are sacrificed to a greater or lesser extent to achieve this. However, for research and for some practical applications like thickness gauging, it would often be convenient to work with less efficient probes provided that these were short-pulsed and could be manufactured in a reproducible manner. This paper describes one route to the construction of such a probe.

In many spectroscopic and interferometric applications, the plate separation of a Fabry-Perot etalon has to be repeatably stepped or scanned over at least one free spectral range. A convenient technique for adjusting the plate separation of an etalon is by means of piezoelectric transducers which may be stabilised by a capacitance micrometer servo-loop. Several optically-contacted etalons have been constructed where the capacitive elements are integral features of the three spacers which also incorporate the piezoelectric transducers. Due to the optical contacting used throughout the device, the etalon is stable against mechanical shock and vibration for most laboratory and field applications. For space-flight applications, however, the spacers have been bonded using cyanoacrylate adhesives.

The long wavelength of a CO₂ laser produces significant speckle pattern effects with practical sized beams and detectors where a diffuser is used to scatter the light on to the detector. The authors found the percentage standard deviation of the signal from shot to shot to be described typically by 36/N where N is the Fresnel number defined by the beam and detector sizes. The polar diagram for normal incidence of a single rough surface such as sand blasted gold shows a strong central peak whilst in-depth diffusers such as stacked salt granules or flowers of sulphur are much more nearly Lambertian-salt being virtually perfect. Various absorbing paints and graphite are also assessed.

When a hard probe of relatively low thermal conductivity is pressed against a number of softer materials of much higher conductivity, the thermal contact resistance should depend only on the radius of contact. Thus, the authors have applied a device, that consists of a heated copper-constantan thermocouple with a ruby tip, to several high conductivity metals and alloys and may have shown that the resultant thermoelectric EMF is directly related to the diagonal length of the indentation produced by a conventional pyramid hardness tester under a given load. They have also found that the probe can be used in studying the hardness of a material that is a poorer conductor of heat but it is then necessary to apply a correction factor.

This article describes an apparatus for DTA and a simple cell suitable for use with a differential scanning calorimeter for high pressure studies. Following the description of the high pressure vessels, the advantages and disadvantages of both apparatus are discussed.