Table of contents

Water vapour concentrations are measured using the optical absorption of a Zeeman-split emission line of an argon discharge lamp. When a longitudinal magnetic field of the proper magnitude is used to split the emission line, two components of opposite circular polarization are produced: one coincident, and one off-resonance with respect to a water vapour absorption line at . Differential absorption is directly measured by alternately selecting the polarization of the light which is allowed to propagate down the optical path into a multipass absorption cell. Water vapour concentration measurements were obtained over a range of over three orders of magnitude (-3.0%). The monitor was also shown to act directly as a mixing ratio (mole fraction) sensor (within ) over a pressure range of 0.3-1.2 atm.

Electrical capacitance tomography (ECT) provides information on the flow regime and concentration distribution in process vessels and pipelines containing two-phase mixtures. This is achieved by arranging sensors around the pipe or vessel to be imaged. The sensor output signals depend on the position of the phases within the sensing zone. A computer is then used to reconstruct an image of the pipe cross section from the sensor measurements. It is necessary to calibrate the ECT system by filling the sensing zone consecutively with the low permittivity material, then the high permittivity material. When the high permittivity material is introduced into a low permittivity background within the sensing zone, the capacitance between sensors will increase. This paper demonstrates that this calibration procedure coupled with the existing image reconstruction software is inappropriate for imaging liquid-liquid dispersions containing low fractions (below 0.3) of water in kerosene. An alternative calibration procedure is proposed which yields substantially improved images.

This paper gives first of all the definition of the work function of an electronic as well as an ionic conductor. FET-type gas sensors known from the literature are considered in view of this basic theory and the parameter of the work function which is responsible for the sensing properties is noticed. This appears not always to be possible for the various types of gas sensors, in this case the gas FET, the SGFET and the IGFET. In contrast to this ambiguity, the sensing parameters of the recently developed MOSFET, meant for application in an electrolyte, can clearly be identified. As an example an oxygen sensor based on the developed MOSFET is described.

In agriculture, a large variability of objects in a range of sizes and shapes is found, leading to problems in size grading. For example, for a low-cost product such as potatoes, the predominantly used mechanical size-determining systems have errors of up to 30% and can cause damage, but they are cheap and have a throughput up to 20 tonnes per hour. Alternatives which can guarantee an improvement in accuracy and a financial gain for the companies are required. In this paper methods for the determination of volume and axis measurements using a simple ring sensor system are described. A modified co-ordinate system and the segmentation of the area between the ring and the object are used. The volume determination is independent of the direction of presentation of the objects. For the determination of axes, the objects must be presented in the longitudinal direction to allow the use of simple 2D algorithms. The accuracy of the system depends both on the number of transmitters and receivers placed on the ring and on its diameter. A small ring sensor system was developed, which can scan 3D objects in real time (36 000 potatoes, 3.6 tonnes per hour) with an accuracy of better than 5% for a volume larger than 100 .

The use of resonant sensors with high mechanical Q factors is based on a vibrating element acting as a harmonic oscillator. The existence and consequence of non-linearity, for some special resonant structures and above critical values, are not often taken into account. For experiments in which the mechanical deflection gives basically the physical information, a lack of knowledge of possible non-linearity may have dramatic consequences for the exploitation of the results. Different free-standing silicon resonators have been micromachined and an experimental device to test the dynamical properties of these structures has been designed. The resonant structures were electrostatically excited in flexural mode. The results have revealed a spectacular non-linear behaviour of the thin films at ambient temperature. It is well established that this anharmonic behaviour is linked to the mechanical properties of these resonators rather than to the electrostatic excitation. The experiments have revealed three different types of non-linear behaviour. These experimental results are presented and analysed starting from the non-linear differential equation.

A practical model for evaluating the calibration uncertainty of force-measuring devices is presented. The method suggests that the calibration uncertainty components of force-measuring device arise from the calibration system, force-measuring device, interaction between the calibration system and force-measuring device, and the resolution of the indicator. The basic mathematical models for uncertainty evaluation arising from the resolution of the indicator and rotation effect are proposed. The present model has been incorporated in the uncertainty evaluation of the force measurements. Some experimental results are presented to demonstrate and support the present model.

A sensor multiplexing scheme for the simultaneous monitoring of dynamic strain and temperature is presented. The scheme combines low-coherence and wavelength-division signal processing with a serial array of fibre-Fabry-Pérot (FFP) interferometric sensors defined by in-fibre grating mirrors of matched Bragg wavelength. Heterodyne measurements of signal phase from a 39 cm long FFP interferometer result in a dynamic strain resolution of about at acoustic frequencies. Temperature measurements via the induced changes in Bragg wavelength have a sensitivity of about . The cross-talk between the strain and temperature channels is within the system noise.

We present a simple method for directional discrimination in laser Doppler anemometry (LDA) without using frequency shifting components. The measuring volume is imaged onto a twinned pair of receiving fibres, each of semi-circular cross section, which permit the separate detection of the leading and trailing part of the burst signal, thus revealing the sign of the velocity component without the need for frequency shifting elements. Besides being very straightforward and inexpensive, this method is particularly apt for fibre coupled LDA measuring devices.

The low-frequency limit normally imposed by a confined water tank in underwater acoustic transducers is prominently reduced by applying Prony's model to the sampled transient data. A new concept to improve the calibration accuracy of transducers with an uneven transmitting response is presented, i.e. that variation of transmitting characteristics of transducers with frequency can be compensated by using devised minimum phase signals. Its effectiveness is demonstrated in the experiments.

The virtual current of an electromagnetic flow meter in partially filled pipes is obtained by an alternating method. Some typical distributions of the weight function under a uniform magnetic field are given. Changes of the non-uniformity of the weight function versus the fluid's depth as well as the electrode's angular position are calculated and discussed.

The directional sensitivity of a new liquid crystal technique for aerodynamic skin friction measurement has been assessed. Experiments were performed using a turntable device installed in a laminar flow duct. Nematic liquid crystal was deposited onto the centre of the turntable. Various initial liquid crystal layer orientations (turntable angles) and magnitudes of applied skin friction were investigated. The dynamic and steady state response was measured using the transmission of polarized monochromatic light. Steady state predictions based on a simple director model are shown to be in reasonable agreement with the experimental results. The current results demonstrate the potential of the nematic technique in skin friction vector measurement applications.

We present a new top-loading vacuum insulated thermostat/cryostat for temperature-modulated differential scanning calorimetry (TMDSC) and DSC measurements covering an outstanding temperature range. TMDSC measurements are now possible down to 60 K. As a consequence of its construction features, contamination by moisture is completely eliminated. In particular, the important time domain technique can be applied without any time limit, thus allowing precise measurements even in the immediate vicinity of phase transitions. Experimental results are presented to show the performance of the modified TMDSC system.

The -method is used to study time dependent processes through measurements of dynamic heat capacity. The -sensor is a thin metal strip which is evaporated onto a substrate. The sample is probed by periodic diffusive thermal waves of frequency emitted from the strip. The heater temperature measured at frequency yields the dynamic heat capacity. The validity of a one-dimensional heat flow model, assuming an infinitely thin heater, is here studied using a finite element modelling (FEM) technique as well as experiments. To obtain results within 1% of the theory, FEM shows that the ratio between the heater width and the heat wave penetration depth (, where D is the thermal diffusivity) must be greater than 30, which sets a low-frequency limit for the model. At high frequencies, the finite thickness of the heater causes a deviation from the model. For a thickness of , the deviation is at 200 Hz, reaching 5% at 5 kHz. A small -component intrinsic to the electronics together with a thermal resistance between heater and sample can explain deviations from , at high frequencies, where is predicted by the model but experiments generally show smaller values.

An application of quartz crystal resonator measurements for characterization of polymer materials is presented. It exploits the non-gravimetric response of these resonators, namely the dependence of the electrical response of polymer-coated quartz crystal resonators on the polymer's shear modulus. The possibility and an acoustic limit for this method for determination of shear moduli are discussed. It is shown that this application of quartz crystal resonators is in contrast to the well known mass detection according to gravimetric working conditions. An error analysis for the gravimetric frequency interpretation for polymer-coated crystals is presented.

We have studied the relationship between the acoustic properties of a near-field acoustic sensor and the properties of a liquid. An acoustic stepped horn is driven by two piezoelectric elements. The generated acoustic waves cause the solid horn to resonate and an acoustic load at the tip modifies these oscillation modes. This leads to a change in electric impedance at the piezoelectric elements. This sensitivity to acoustic load allows a study of semi-infinite liquids. We found a relation between the resonance frequency and the liquid density and a relation between the electric impedance and the viscosity.

A high-voltage trigger generator has been developed to trigger an in-line plasma closing transfer switch. The trigger generator is capable of producing 70 kV voltage pulses, having a rise time and duration of 10 and 60 ns respectively. It uses a stacked Blumlein cable generator fired using a triggered corona stabilized (TCS) switch and is fully controllable in frequency from single shot up to 10 kHz in a burst mode. The device is very compact, portable and is operated via a fibre optic link from a solid state pulse generator. The trigger generator can also be used as a fast high-voltage, high peak power and high-frequency driving device.

The objective of this design note is to discuss and define the total uncertainty in temperature calibrations by comparison, by analysing most of the likely error sources. As a result of the proposed and developed uncertainty analysis, further reductions of uncertainties could be realized if/when better equipment becomes available. The analysis is performed as a case study using state-of-the-art calibration equipment described in the design note. This equipment is located in the authors' own secondary temperature calibration laboratory. Accreditation for this laboratory has been granted through The Dutch Council of Accreditation (RVA) for calibrations in the temperature range -55 to C. In temperature calibrations by comparison the four main groups of uncertainties are the reproducibility, uncertainty of a reference thermometer, uncertainty of a calibration bath or a furnace and uncertainty of a measuring device. Special care is taken, using a thorough evaluation procedure, to ensure that the uncertainty contribution of the calibration bath or furnace is as low as possible. This is necessary because the total uncertainty assigned to an instrument under calibration is larger than the largest individual uncertainty contribution. In temperature calibrations the largest uncertainty is most likely to be the uncertainty of the calibration bath or a furnace. Therefore this uncertainty typically represents the lowest limit for further reduction of the total uncertainty of the calibration process. The analysis performed allows optimal use of temperature calibration equipment for calibration of thermometers by comparison. In this way most practical calibration needs are satisfied in a more economical way than by using substantially more expensive fixed point calibrations.

For different applications of the pulsed-laser deposition (PLD) technique and for particular PLD chambers, different multi-target carousels are required. Here we describe three designs of a multi-target carousel for PLD which present separately the advantages of sufficient target cooling, reduced probability of jamming in operation and an adjustable target-to-flange distance. These carousels can be applied in various simple and small PLD systems where commercial products are not suitable, as well as in laser-molecular-beam-epitaxy (L-MBE) systems. They are of simple structure, low cost and may be constructed in a normal workshop.

A simple quartz furnace for Mössbauer measurements is described. The construction allows long time operation at temperatures up to 1500 K.