Table of contents

The word 'mechatronics' provides a focus for the integration of electronic hardware and computer software with mechanical engineering in a product or process. Sensors and sensing systems are integral to the functioning of mechatronic systems as providers of the process and procedural data on which their operation is based. In particular, development of digital control systems has been supported by increases in performance, reducing real costs, of the associated electronic processing, which has led to development of dedicated controller architectures based on use of application-specific integrated circuits. In the area of sensor development, the driving force is the silicon-based technology that can provide both the signal processing element in the form of the integrated circuit but increasingly also the sensing component, often on the same chip. Additionally, development of the techniques of micromachining has enabled production of complex structures on a chip, some of which, when combined with on-chip sensing and processing, may be considered to be mechatronic in their own right. The paper therefore reviews the role and importance of sensors and measurement systems within mechatronics and illustrates this with examples drawn from manufacturing, vehicle systems and domestic products.

Four 1 kg stainless steel weights were used to carry out comparisons to investigate the efficiency of different procedures for cleaning precision mass standards. Not only were mass comparisons carried out on a high-resolution 1 kg comparison balance but also the surface layers of 1 kg mass standards were directly determined for the first time using an automatic ellipsometer. Both measuring techniques show that ultrasonic cleaning in ethanol is the most efficient procedure for cleaning polished stainless steel surfaces. Furthermore, it was possible to prove that ellipsometry as an optical technique of surface analysis is well suited for non-contact, highly sensitive and absolute determination of the surface cleanliness of mass standards.

A simple design for evaluating the X-Y distribution of electric fields is presented. The apparatus is optical fibre-coupled and allows measurements without physical contact. The details of the device, some applications and its potential use in various fields are discussed.

The high-performance and concurrency features of transputers and a mixed-grain approach to parallelism are exploited to provide an existing differential scanning calorimeter with real-time computational capabilities which can be easily increased by addition of transputer-based modules. The effectiveness of our design is tested by investigating the behaviour of aqueous solutions of a biomolecule, whose time-dependent heat capacity is evaluated and visualized while the experiment is in progress. The reported hardware/software details can be profitably used to update different existing instrumentation.

A new pyrometric method was used to measure the evolution of the surface temperature of a metallic target at the end of a powerful laser pulse. The method uses the property of a metallic surface to polarize the reflected and emitted lights in different ways. Surface temperatures in the range 2000-5000 K were measured through the strongly radiative plasma.

A sensitivity analysis of the two-colour pyrometry technique for calculation of soot temperature T and volume fraction f_v is presented. Two different combustion environments are exemplified for high (f_v approximately=10^-5) and low (f_v approximately=10^-7) soot concentration regimes. The calculations are carried out taking into account particle shape, different expressions for monochromatic emissivity, optical property variations, size distribution of soot particles and a finite light-detection bandwidth. The results indicate which spectral range, for the choice of the ( lambda ₁, lambda ₂) wavelengths employed in the emission measurements, and computing algorithm, for the reckoning of the T values, can be appropriated to guarantee a lower a priori uncertainty in the T and f_v calculated values. Results stress the evidence that T and f_v values are critically sensitive to the complex refractive index, m=n-ik, and that they are irrelevantly influenced by the probability distribution of particle size. The critical theoretical influence of the type of fuel, characterized by a different soot hydrogen/carbon ratio, upon the inferred f_v values is assessed. Determinations of temperature values with ( lambda ₁, lambda ₂) measurement wavelengths above 1.2 mu m is demonstrated to be invalidated by an uncertainty contribution of at least 20 K in the regime f_v approximately=10^-5 and 100 K in the regime f_v approximately=10^-7.

A highly automated torque magnetometer has been designed, mainly for measuring standard sized rock samples. By employing two hinges of crossed leaf-springs it was possible to integrate a stepper motor in the sample holder for the rotation of the specimen in the external magnetic field. The dynamic range of the instrument covers the torque signals of most rock types. Additionally the instrument is able to measure the magnetocrystalline anisotropy of monocrystals.

A technique for simultaneous independent measurement of temperature and magnetic field in a Faraday-effect magnetometer is presented. The technique is based on interferometric phase measurement of temperature combined with magnetic-field-induced visibility modulation of the interferometric fringes. The technique is demonstrated using a paramagnetic FR-5 glass sensing element in a Michelson and a low-finesse Fabry-Perot configuration. The optical configuration is shown to be capable of remote operation using fibre-optic links. The measurement of temperature is shown to enable compensation of the scale factor for the temperature-dependent Verdet constant. Unlike in all previously reported techniques, the temperature is measured over exactly the same optical path as that subject to the magnetic field.

This paper describes the development and operation of two dual-probe interference systems for detection of surface acoustic waves. Both systems operate by comparing the surface displacement under each probe, thus enabling the surface wave velocity to be determined. In the so-called direct interference system the two probe beams are made to interfere with each other whereas in the indirect interference system each probe beam is made to interfere with a common reference. The relative merits of each system are compared in detail and experimental results showing operation of the systems are presented.

The first application of a thinned back-illuminated ion-implanted and laser annealed CCD as a detector for extreme ultraviolet spectroscopy is described. The observed stigmatic spectra are in the 40-70 nm region and are produced by the excitation of some noble gases in an open hollow cathode source installed in a normal incidence toroidal grating spectrograph. The results are compared with spectra obtained by other detector systems applied to the same instrumentation, showing that the CCD offers a much greater detection capability than a system using a converting scintillator and a comparable one with respect to a photon counting detector.

The design and construction of an X-Y position-sensitive detector based on a delay-line anode assembly mounted behind a multichannel plate electron multiplier are described. The dead-time is less than 60 ns for all particle pairs, and can easily be reduced further.

An instrument which measures the amount of light scattered by cloud water droplets and subsequently calculates the extinction per metre (i.e. the atmospheric visibility) of the cloud is presented. The instrument has proven capable of measuring visual range in or out of cloud, is capable of measuring extinctions down to 0.0003 m^-1 and has operated continuously in the field for periods in excess of a year without servicing, providing remote continuous on-line monitoring of cloud conditions on a ten minute averaged basis. This forms an integral part of a larger project to calculate the annual sulphate and nitrate deposition at elevated sites. The primary objective of the instrument is to measure the extinction due to water droplets; however, it can be adapted to provide the approximate liquid water content appropriate to the extinction it measures. Apart from being a valuable research tool, it is also suitable as an early warning device in situations where detection of ground level cloud (i.e. fog) is important, e.g. on motorways, and may be used to activate other instruments which need to operate only under certain conditions.

The beam 'diameter' or 'spot size' and the spatial distribution of power density at the focal point of the high-power laser beams used in laser materials processing applications are fundamental process parameters. The ability to measure these process parameters accurately is essential for effective control of these laser materials processes. In this two part article, the theory and application of a rotating-wire type laser beam analyser (LBA) device for measurement of both the spatial distribution of power density and beam 'diameter' of a converging/diverging (focused) high-power laser beam are presented. In this article, theoretical analyses using geometrical optics are presented for the determination of the sampling path through the beam, the spatial resolution of the LBA, and the transformation relationship between the output voltage versus time signal produced by the LBA detector and the desired power density versus spatial position data. The analyses showed that operation and correct interpretation of measured results from the LBA are strongly dependent upon the relative position of the LBA measurement plane and the laser beam focal plane. This work shows that the LBA can be used to measure the spatial intensity distribution of unattenuated, focused laser beams from high-power lasers.

The theory and application of a rotating-wire type laser beam analyser (LBA) device for measurement of both the spatial distribution of power density and beam 'diameter' of a converging/diverging (focused) high-power laser beam are presented. In part 1 of this article, geometrical optics were used to analyse the theory of operation of the LBA. These analyses showed that operation and correct interpretation of measured results from the LBA are strongly dependent upon the relative position of the LBA measurement plane and the laser beam focal plane. In this article the results of LBA measurements of the laser power density distribution from a 250 W mean power, pulsed Nd:YAG laser welder are presented and compared with the derived theory of operation of the LBA. The sample area path of the LBA through the laser beam was determined experimentally and was found to agree with the theoretically predicted path. Also, the theoretically predicted effects of sample area dimensions relative to the measured beam diameter on distortion of the measured power density distribution were confirmed experimentally. Finally, LBA measurements made near the focal point of beams from the high-power pulsed Nd:YAG laser were shown to agree with measured beam 'diameter' and power density distributions obtained using the Kapton film burn pattern technique. It is shown that with careful operation and interpretation of measured results, the LBA can be used to measure accurately the spatial distribution of power density and the beam 'diameter' of unattenuated, focused laser beams from high-power lasers.

A simple, rugged, absolute calorimeter is described, based on an inversion of Fitch's method for thermal conductivity determination. This calorimeter operates in the range of 0-10 W with linearity of 0.15% over this power range. The minimum detectable power change is 10 mW. The response time of the calorimeter depends on the configuration adopted to absorb the input power, and can lie in the range from 48 to 405 s, depending on the diameter of the calorimeter absorbing region. Results obtained from acoustic power measurements at 1 MHz are demonstrated. Its use is not confined to ultrasound power measurements.

This paper presents a method of void fraction measurement based on a technique of pulse width modulation in response to the changing electrical impedance of a gas-liquid mixture flowing through vertical narrow tubes. The calibration of time-averaged pulse width against void fraction, prepared for an air-water flow, shows that their characteristics are different in different flow regimes. Further calibrations obtained with superficial liquid velocities (U_LS=1.16, 0.65 and 0.16 m s^-1) in slug and churn flow show their sensitivity to U_LS. No such effect is observed in bubble and annular flow regimes. These effects of flow regimes and U_LS could be specified in terms of the number and position of the peaks of the probability distribution function (PDF) of pulse width data. For a given system, these recorded PDF data help in determining the calibrations uniquely in all unknown flow regimes and void fractions ranging from 0 to 100%.

A relatively simple He-Ne laser anemometer arrangement has been developed for detection of Reynolds stresses, namely those shear stresses that play a dominant role in turbulent fluid dynamics. After a brief discussion of some common anemometer systems, which are provided also for two-component measurements, the detection method is described in more detail. Its efficiency is demonstrated in a highly turbulent shear flow (free-mixing layer) of water as well as of a polymer solution, showing strong drag reduction. Results are given not only about the Reynolds stress distribution but also about the temporal structure, namely the cross correlation of two turbulent fluctuations across the mixing layer.

This paper describes an integrated experimental procedure for obtaining accurate measurements with both single normal (SN) and X hot-film probes in water flows. The first part of the paper describes techniques developed to overcome the common problems of temperature variations and contamination in a recirculating test facility, leading to long-term calibration stability. The second part of the paper describes the development of fast, reliable and accurate computer-based calibration methods for both SN and X probes. The final section of the paper describes comparative measurements between an SN and an X probe in vertical upward water pipe flow, demonstrating the validity of the methods developed.

Experimental techniques to study shocked substances are described. They include specimen loading by an oblique damping shock wave and impulsive X-raying. The method makes it possible to obtain a dynamical picture with an oblique shock wave, a moving free surface, the back boundary of a spall layer, and so on. The values of parameters and spall damage may then be calculated.

The operation of a leaky zirconia oxygen pump-gauge is discussed in which the pump was driven so as to generate a sinusoidal EMF at the gauge of predetermined frequency and amplitude. A theoretical equation for the current is derived and checked for conformance with sensor characteristics. In general there was good agreement with theory; there was some discrepancy with variation in total gas pressure. It is shown that the output current I₀ at zero gauge EMF was independent of the degree of leakage while the current I_pi/2 at the gauge EMF maximum was directly proportional to the degree of leakage, so providing a direct and independent measure of leakage with aging.

Distortions of nuclear energy spectra at high counting rates have been efficiently reduced by two different signal processing methods: pile-up suppression by pulse shortening and pile-up rejection by detection and rejection of the piled-up pulses. By combining these methods new circuits have been developed increasing the limit for the quality gamma ray spectrometry from available, up to now, 100000 s^-1 to the range of up to 500000 s^-1.

In the measurement of dielectric properties the HP 4192A low frequency analyser has been increasingly used. Under certain conditions, at low frequencies, this instrument can give misleading results for the real component epsilon ' of permittivity.

A novel high-voltage pulse generator, which can provide a rapid high-voltage, low-energy pulse followed by a high-energy capacitive discharge, is described. The generator simulates a high-voltage, high-energy pulsed power source without resorting to high-voltage, high-energy capacitors., The pulse-forming network is capable of generating a high-voltage pulse of up to 350 kV, and the capacitor bank can provide a high-current pulse of several tens of kilo-amperes.