Table of contents

NATA operates Australia's national laboratory accreditation system covering 10 fields of testing. Instrument laboratories fall into a number of these fields which include both calibration and testing. Inter-laboratory testing in the measurement areas has included voltage and resistance measurements, and calibration of thermometers and standard lamps. The authors discuss NATA's role in the Australian measurement system with particular emphasis on laboratories accredited in the various areas of applied physics, the benefits of laboratory accreditation and the requirements for using digital instruments as reference standards.

Holography offers unique advantages over conventional photography or traditional photogrammetric techniques in the recording of three-dimensional objects over a large depth of field. However, there are several fundamental problems in recording and replay that must be understood and overcome. The authors discuss the techniques of in-line and off-axis holography, and the problems that are encountered in practice. They present a review of several applications in particulate recording, bubble chamber holography, fuel-rod 'hologrammetry', endoscopy etc. The emphasis is on precision three-dimensional coordinate measurements from holographic images.

A novel mechanically scanned and non-contacting surface profiling instrument has been developed in which a fine wire probe is raster scanned over the surface of the sample under examination. Measurement of the modulated capacitance between the probe and the vibrated sample is used to maintain the probe just above the surface. In the prototype instrument described, an in-plane resolution better than 2 mu m is achieved by the use of an etched tungsten wire probe, while the perpendicular resolution is 6 nm. Both insulating and conducting samples may be scanned and the technique makes it possible to measure electrical properties of the surface under the probe as well as the surface microtopography.

A phase-shifting PLL frequency offsetter has been developed for use in the comparison of near-equal frequencies by phase-time recordings. The input frequency is shifted by means of a phase-shifting phase-locked loop. Time-linear phase shifting is simply obtained by inserting an RC link in the loop. Continuous operation is obtained by polarity switching of the capacitor and the phase detector at suitable phase values. An experimental circuit working around 114 kHz is presented, providing offset frequencies in the range 1 mHz to 10 Hz. The circuit uses eight analogue ICs. The output frequency stability depends on the input frequency stability, the fractional frequency offset and the stability of the analogue circuit, and is, for the circuit presented, a few parts in 10¹⁰ at an offset frequency of 0.01 Hz if the input frequency is based on a Cs or Rb source. The method can be used for frequencies up to the MHz range.

A new system of measuring and evaluation has been developed which is suitable for recording both arc motion and structure in any device, even through opaque walls. Experiments on a large scale can be performed with economy in time and expense. The system consists of optoelectronic sensory equipment, a transient recorder, a process control computer and a terminal or plotter.

A microcomputer-controlled apparatus for the simultaneous measurement of the conductivity and the Seebeck coefficient of thin solid films is described. The investigated temperature range lies from room temperature to 1100 degrees C. The apparatus was tested on thin films of oxides produced in argon gas by RF sputtering. It is shown that the noise in the measured quantities is small enough to allow a further discrimination between the various models of electron transport. The overall noise in the thermopower is 1.5%, whereas it is 3*10^-3 for the conductivity. It is found that noise is essentially an electronic noise and so could be improved.

Design details of a new Langmuir-Blodgett trough are presented. It uses a diamond-shaped barrier which flexes at the corners to alter the area, giving high cleanliness and a constant perimeter. The amplitude of surface waves is of the order of 1 mu m (mostly due to background noise), and the uncertainty in the area of the diamond-shaped barrier is less than 1.5%. Trough performance was evaluated using eicosanoic and tricosanoic acid, both on subphases containing cadmium ions. Good stability of the surface monolayers and sharp phase transitions indicate that high levels of cleanliness are possible. Isotherms show excellent reproducibility. Surface flow patterns during deposition are satisfactory, and film quality is high, as judged from microscopic examination and preliminary optical and electrical studies.

A simple design for a high-performance DC resistance thermometer bridge is presented. The bridge takes advantage of low-drift, low-offset operational amplifiers to obtain the low noise levels and flexibility previously available only from AC bridges. The characteristics of the bridge's performance are discussed and spectral measurements with the circuit are considered.

A time domain reflectometry (TDR) set-up is described which has been designed to measure the ionic conductivity within the range of 0.01 Omega ^-1 m^-1 to 100 Omega ^-1 m^-1 and the permittivity of ionically conducting solid materials at frequencies between 10 MHz and 10 GHz. With the TDR set-up one can measure these properties at temperatures up to 1300K by employing the lumped-capacitance method. A new theoretical approach for this lumped-capacitance method along with an error discussion is presented. The applicability of TDR to ionic conductors is demonstrated by results obtained for a SrF₂ single crystal doped with 32 mol.% CeF₃. The measured conductivity of the crystal at low temperatures (300 K) shows a dispersion with the frequency, whereas at temperatures around 1000 K frequency-independent ionic conductivity is observed. From an Arrhenius plot of this frequency-independent ionic conductivity the activation energy has been obtained.

Describes the theory, design and performance of a linear coil used to measure distributed current pulses. The linear-wound coil acts as a delay line. Its response to transient signals is studied for a generic excitation and for various terminating impedances. The probe rise time is less than 1 ns, the attenuation is about 5.3 mV A^-1 and it can record currents up to tens of kA.

The increasingly arduous demands of operating environment and quality targets in electric arc welding applications have led to the need for instrumentation to permit the detailed assessment of the performance of welding power units. The construction and repair of undersea oil and gas pipelines is one such demanding application. An instrument is described which allows the detailed statistical monitoring of arc voltage, together with other status variables. The instrument provides the high resolution required in recording short-lived arc transient phenomena, but with relatively modest data-store needs. It is based upon a proprietary microcomputer with added interface hardware and purpose-designed software; both aspects are described in overall terms, together with a discussion of the performance of the system. A case study is also included to illustrate the use of the instrument as part of a comprehensive testing facility for the evaluation of welding regimes and systems under hyperbaric conditions up to 40 bar (4 MPa).

An interferometric-based optical processing system for signal enhancement purposes is described. The technique utilises characteristic optical coherence properties of the signal. The results of the study have indicated a good correlation between theoretical predictions and experimental measurements. An improvement in the signal-to-clutter intensity ratio of 1.6*10⁷ for laser/white light discrimination has been achieved. Also, for a non-laser signal with a spectral bandwidth of +or-7 nm (FWHM), a gain of 1.4*10³ has been obtained. These results were achieved without the use of sophisticated electronic signal recovery techniques.

A double-beam acousto-optic time-integrating correlator is described that is a modification of a recently reported acousto-optic interferometer. The instrument uses a pair of Kosters double-image prisms and two tellurium dioxide Bragg cells to produce the correlation function of pulsed radio signals.

A method for monitoring laser beam powers is described, based on piezoelectric detection of the photoacoustic effect in an absorbing material. The response of the device is comparable with that of power meters based on gas-microphone detection of the photoacoustic effect.

A method is proposed for processing IC waveforms acquired using the stroboscopic waveform mode. The waveforms are modelled using first-order exponentials and least-squares regression is used to fit the model to the measured waveform. The method is particularly suited to an automated EBT system. An error analysis is included which highlights the relationship between the signal-to-noise ratio of the signal being measured and the phase-shift increment and pulse duration of the beam-blanking unit.

A technique is described which uses an electron spectrometer fitted with a position-sensitive multidetector to measure the electron energy-loss spectra of atoms and molecules as a function of electron impact energy. This gives information about resonances in the excitation functions of excited states. The technique has been used to make measurements of differential cross sections for the excitation of vibrational levels of the ground state of nitrogen. The ² Pi _g shape resonance at about 2 eV has been studied and absolute cross sections for this process have been deduced.

A new apparatus which uses laser-induced fluorescence to determine the nuclear as well as the valence electron spin polarisation of desorbing ²³Na atoms is presented. Thus the limitation of previous NMR experiments on chemisorbed alkali-metal atoms to the detection of desorbing ions and hence to hot surfaces with a high workfunction ( Phi >or=5 eV) are overcome. The experiments can now be extended to hot surfaces with a low workfunction. The new possibility of determining the valence electron spin polarisation of desorbing atoms extends the method to the investigation of the physisorption of Na atoms. Electron spin resonance experiments on adsorbed Na atoms are also now feasible. The method is demonstrated with two examples: an NMR experiment on a W(112) surface and the study of a physisorption-chemisorption transition of Na atoms due to coadsorption of hydrocarbons on a metal surface.

Microprocessor control of an iodine-stabilised ion laser is described. This control is achieved using an STD-bus based Z-80 processor and standard STD input/output cards to interface with the various laser transducers and detectors. Automatic control functions include laser wavelength selection and optimisation, laser current and intensity control, and high resolution frequency scanning with recognition of, and stabilisation to, selected saturated iodine features. Automatic switching between iodine-stabilised Kr⁺ ion laser wavelengths at 568 nm and 531 nm is specifically described.

An all-solid-state pulser for the excitation of repetitively pulsed gas lasers is described which uses thyristor switching followed by a ferrite core pulse transformer and a four-stage pulse compression system using DC biased ferrite magnetic switches. An analysis of energy losses in the complex high voltage circuit is made, and an energy conversion efficiency of 73% overall is shown to be obtained, using commercially available ferrite materials. Interfacing of the circuit to the TEA CO₂ laser is discussed.

Describes a study of the accuracy and suitability of hot-wire velocity calibration relations for implementation on a micro/minicomputer. The investigation has covered simple and extended power laws, polynomial fits of three types and spline fits. The main part of the investigation was related to a typical moderate velocity range of 3-30 m s^-1, with complementary data being presented for a large velocity range, 4-90 m s^-1, and at low velocities, 1-6 m s^-1. By careful attention to measurement errors, the suitability or limitations of the various calibration relationships have been identified. Optimisation for both accuracy and computational convenience identified no simple method as being the best, but three methods: simple power law or a fourth-order polynomial in E or a third-order polynomial in E², were shown to give similar results.

Information on the integrated gas consumption is required whenever liquid or solid gas sources are used in order to indicate when a source has to be renewed. The authors present a simple, inexpensive electronic integrator in conjunction with thermal mass-flow meters or controllers which can be used where visual control is not possible or desirable.