High Rate Measurements Research Articles

Fiber-Optic Sensor Interrogation Based on a Widely Tunable Monolithic Laser Diode

Fiber-optic sensors have experienced great interest in research and development since their invention. Dedicated measurement systems are essential for utilization and development of these sensors. Instruments based on tunable lasers are established devices for the demodulation of such sensors. We introduce and demonstrate a tunable laser measurement system based on a widely tunable monolithic laser diode (TML). It is capable of demodulating different types of fiber-optic sensors, although we focus on the interrogation of fiber Bragg grating (FBG) sensors. The rapid tuning of the laser's wavelength is critical for achieving high measurement rates. However, the high tuning rate is demanding and requires careful characterization. We present a method for this and show, to our knowledge for the first time, data on the rapid tuning through the whole spectrum of this type of laser diode. We propose a modified centroid algorithm that can cope with nonequidistantly sampled spectra caused by the laser's functional principle. Finally, we demonstrate the dynamic performance of the new measurement system in an application: An FBG-based acceleration sensor is demodulated at a 5-kHz sample rate during a vibrational test showing the potential of the approach.

Processes controlling rapid temperature variations on rock surfaces

AbstractIn arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0·375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C min−1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C min−1 and the average percentage time spent above 2°C min−1 was ∼70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C min−1. Simultaneous measurements of two thermocouples 5·5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ∼10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.

Relativistic cyclotron radiation detection of tritium decay electrons as a new technique for measuring the neutrino mass

The shape of the beta-decay energy distribution is sensitive to the mass of the electron neutrino. Attempts to measure the endpoint shape of tritium decay have so far seen no distortion from the zero-mass form, thus placing an upper limit of m{sub {nu}}{sub {beta}}<2.3 eV. Here, we show that a new type of electron energy spectroscopy could improve future measurements of this spectrum and therefore of the neutrino mass. We propose to detect the coherent cyclotron radiation emitted by an energetic electron in a magnetic field. For mildly relativistic electrons, like those in tritium decay, the relativistic shift of the cyclotron frequency allows us to extract the electron energy from the emitted radiation. We present calculations for the energy resolution, noise limits, high-rate measurement capability, and systematic errors expected in such an experiment.

Laser Doppler sensor employing a single fan-shaped interference fringe system for distance and shape measurement of laterally moving objects

For monitoring the position and shape of fast moving and, especially, rotating objects such as turbo machine rotors, contactless and compact sensors with a high measurement rate as well as high precision are required. We present for the first time, to the best of our knowledge, a novel laser Doppler sensor employing a single fan-shaped interference fringe system, which allows measuring for the position and shape of fast moving solid bodies with known tangential velocity. It is shown theoretically as well as experimentally that this sensor offers concurrently high position resolution and high temporal resolution in contrast to conventional measurement techniques, since its measurement uncertainty is, in principle, independent of the object velocity. Moreover, it can be built very compact, because it features low complexity. To prove its operational capability and its potential for practical applications, radial and axial shape measurements of rotating bodies are demonstrated in comparison with triangulation. An average position resolution of about 2 microm could be achieved.

Measurement uncertainty and temporal resolution of Doppler global velocimetry using laser frequency modulation

A Doppler global velocimetry (DGV) measurement technique with a sinusoidal laser frequency modulation is presented for measuring velocity fields in fluid flows. A cesium absorption cell is used for the conversion of the Doppler shift frequency into a change in light intensity, which can be measured by a fiber coupled avalanche photo diode array. Because of a harmonic analysis of the detector element signals, no errors due to detector offset drifts occur and no reference detector array is necessary for measuring the scattered light power. Hence, large errors such as image misalignment errors and beam split errors are eliminated. Furthermore, the measurement system is also capable of achieving high measurement rates up to the modulation frequency (100 kHz) and thus opens new perspectives to multiple point investigations of instationary flows, e.g., for turbulence analysis. A fundamental measurement uncertainty analysis based on the theory of Cramér and Rao is given and validated by experimental results. The current relation between time resolution and measurement uncertainty, as well as further optimization strategies, are discussed.

Wideband impedance spectrum analyzer for process automation applications

For decades impedance spectroscopy is used in technical laboratories and research departments to investigate effects or material characteristics that affect the impedance spectrum of the sensor. Establishing this analytical approach for process automation and stand-alone applications will deliver additional and valuable information beside traditional measurement techniques such as the measurement of temperature, flow rate, and conductivity, among others. As yet, most of the current impedance analysis methods are suited for laboratory applications only since they involve stand-alone network analyzers that are slow, expensive, large, or immobile. Furthermore, those systems offer a large range of functionality that is not being used in process control and other fields of application. We developed a sensor interface based on high speed direct digital signal processing offering wideband impedance spectrum analysis with high resolution for frequency adjustment, excellent noise rejection, very high measurement rate, and convenient data exchange to common interfaces. The electronics has been implemented on two small circuit boards and it is well suited for process control applications such as monitoring phase transitions, characterization of fluidal systems, and control of biological processes. The impedance spectrum analyzer can be customized easily for different measurement applications by adapting the appropriate sensor module. It has been tested for industrial applications, e.g., dielectric spectroscopy and high temperature gas analysis.

Phase-Error Measurement and Compensation in PLL Frequency Synthesizers for FMCW Sensors&amp;mdash;I: Context and Application

The synthesis of linear frequency sweeps or chirps is required, among others, in frequency-modulated continuous-wave radar systems for object position estimation. Low phase and frequency errors in sweeps with high bandwidth are a prerequisite for good accuracy and resolution, but, in certain applications where high measurement rates are desired, the additional demand for short sweep cycles has to be met. Transient phenomena in dynamic synthesizers as well as nonlinear system behavior usually cause unknown phase errors in the system output. For the class of phase-locked-loop (PLL)-based frequency synthesizers, a novel output phase-measurement method and dedicated circuitry are proposed that allow significant reduction of phase errors by adaptive input predistortion. The measurement procedure is implemented within the PLL control circuitry and does not require external equipment. The application of this method to PLL system identification and linearization of extremely short frequency sweeps is shown

Active vision applications to cultural heritage acquisition and monitoring

Abstract This paper presents features and performances of a portable stereo active vision system (AVS), designed and built for data acquisition and monitoring of medium-scale monuments and environments of interest for cultural heritage. The research activity was partially carried out in the framework of PARNASO-SIINDA project 1 , a national project aimed at the development of new techniques for cultural heritage preservation, and the case-of-study of the activity was the Roman Theatre of Aosta (IT). Reliable data acquisition and monitoring of the surface alterations related to the monument degrade was a project demand that motivated the stereo vision approach because of its high spatial sampling rate, high accuracy and close correlation of shape and color measurements. The AVS system architecture is designed around three CCD cameras mounted on three independent pan-tilt stages under computer control. The cameras are equipped with different focal lens objectives, allowing the system to acquire both geometric and colorimetric information of an architectural surface (monuments, frescoes…) at different scales over areas of tens of square meters. Two cameras form a stereo pair and are equipped with long-focal objectives to sample a limited portion of the scene at high spatial resolution, while the third one is equipped with a wide-angle objective and it is intended for surveying the whole scene at low-resolution. Geometric measurements are carried out both by forward triangulation of the optical axes of the stereo pair during fixation of an object and by three-dimensional (3D) object reconstruction from the images of the stereo pair. The fixation process is performed by a PC-controlled image-based servo loop. The fixation approach supplies sparse but accurate 3D measurement in the AVS reference system, while the stereo acquisition of image pairs allows a dense 3D local reconstruction of the surface around the fixation point. Colorimetric measurements are performed at pixel level by processing the images of one of the stereo cameras, which is equipped with tristimulus filters. Results are supplied in terms of CIE-Lab components. A user-friendly interface for the system management allows performing several measurements automatically. On-site data processing allows the user to decide for further investigations immediately, if necessary, without expensive delays. The features of the AVS system, namely the working range of depths (2–10 m), the high spatial sampling rate, the accuracy and the close correlation of shape and color measurements, makes the system competitive with respect to other available instruments and techniques for data acquisition and monitoring of small and medium-scale works of art. In the following the AVS architecture is presented, and laboratory tests made to asses its performances are described. Results of the tests and of the acquisition campaign, made on the Roman Theatre of Aosta (IT), are reported and discussed in comparison with other techniques commonly employed in cultural heritage surveys.

High Resolution Ultrasonic Distance Measurement Systems Using Pulse Compression and Their Applications

Ultrasonic distance measurement in air is broadly used for industrial and commercial low cost applications with medium or small resolution. Configurations for the applications are usually restricted to passive reflection and A-B measurement. This paper gives a survey of the ultrasonic distance measurement method with high resolution based on pulse compression. Improvements resulting from this method include good noise suppression, possibility to operate several systems in parallel without disturbing influence of cross talk, and high measurement rate. Modified configurations and the available high resolution lead to new applications which are summarized.

Remote detection and quantification of hot molecular combustion products—experimental instrumentation and determination of optimal infrared spectral micro-windows

Aiming at quantitative investigations of molecular combustion products released from high temperature events (HTE) such as forest fires, volcano eruptions, etc., HTE infrared emission spectra and multi-spectral images are measured from which combustion gas parameters like concentrations and temperatures are determined by solution of the inverse radiative transfer problem. The measurement approach permits air-borne or space-borne remote sensing. Airborne instrumentation includes a Fourier transform spectrometer providing high measurement rates and ruggedness by a rotary scan arrangement covering the mid and thermal infrared bands. The optically co-aligned camera system incorporates the visible/near infrared, mid, and thermal infrared bands. In order to extract high accuracy combustion gas concentrations and temperatures from the measured data, the analysis procedures have to be applied to optimal spectral regions denoted ‘micro-windows’. These are determined by simulations employing radiative transfer models and retrieval procedures along with appropriate molecular spectroscopic data bases such as HITRAN and HITEMP. Simulations and results are presented for the analysis of CO 2 and CO from a flaming forest fire (1000 K) scene. The spectral window 2391.1–2392.2 cm −1 is best suited for retrieving CO 2 column amounts over forest fires and the spectral region 2127.25–2128.25 cm −1 for the CO column. The H 2O column needed for CO retrieval, is retrieved in 2142–2142.6 cm −1.

Covariance Control for Sensor Management in Cluttered Tracking Environments

A simple structure for a high-performance three-dimensional tracking filter is derived in the rotating sensor frame assuming high measurement rates and small angular deviations during target tracking. The resulting three-dimensional estimator consists of three independent filters, whose state includes position, velocity, and acceleration along each of the axes in the rotating sensor frame. Because line-of-sight models for the target acceleration are identical in all three axes and independent, the replacement of the basic exponentially correlated acceleration model by more complicated models preserves the filter structure. Such sophisticated models are based on the multiple model approach.

Monitoring Bench and Procedure for Measurement of the Parameters of Multiport Fiber-Optic Couplers

A monitoring bench and procedure for measurement of the transmission matrix of (N × N)-type multiport fiber-optic couplers using mechano-optical scanning of the bench to achieve a high measurement rate are presented. It is shown that it is possible to measure the elements of the transmission matrix with error at most ±0.2 dB.

Propagation of longitudinal acoustic waves in a thin cylindrical pipe filled with a liquid

In [2, 3], the effect of reducing the wave velocity was found for elastic rods made in the form of a thin strip or fiber and immersed in a liquid. A reduction of the velocity is observed only in thin samples with a thickness on the order of a hundred microns. The effect found is caused by the fact that the so-called boundary layer of a liquid vibrates together with the rod. The thickness of this layer depends on the vibration frequency and the density and viscosity of the liquid. When the sound velocity depends on the viscosity, the effect discovered is employed for the determination of the viscosity of liquids. An advantage of this method is its ability to provide high-rate measurements, which makes it possible to control the chemical reactions with a time-dependent viscosity that proceed in liquids. As a sensor, we used metallic strips and fibers with a diameter of approximately 0.1 mm [2, 3], which were immersed in the liquid under investigation. The use, for this purpose, of a thin capillary filled with the liquid presents a number of advantages, among them the possibility of operating with a very small quantity (specified by the capillary volume) of liquid. The problem of the effect of liquid on the propagation of sound in a thin pipe (capillary) has not yet been solved. The goal of this study is to theoretically seek a solution to this problem.

Optimum analog-to-digital converters for a laser speckle correlation-based displacement and strain sensor with optical preprocessing

We present a novel noncontact measurement procedure to determine displacements of and engineering strains within specimens at very high measurement rates. Appropriate hybrid optical and digital sig- nal processing can be employed to realize two dimensional (2D) corre- lation processing. Due to appropriate optical signal processing, the data acquisition can be performed in one dimension through CCD line-scan cameras. As a result, only 1D digital signal processing algorithms have to be executed and hence the processing power requirements decrease greatly. In this way, the measuring rates are substantially increased. It is shown that optimal Lloyd-Max quantizers implemented in the analog-to- digital converter (ADC) used in combination with a particular digital cor- relation algorithm are able to yield a further increase of the measurement rates compared with standard digital correlation techniques. © 2001 Soci-

The status of immunization measurement and feedback in the United States.

A large body of scientific and programmatic data has demonstrated that provider measurement and feedback raises immunization coverage. Starting in 1995, Congress required that all states measure childhood immunization coverage in all public clinics, and federal grant guidelines encourage private practice measurements. To determine state immunization measurement rates and examine risk factors for high rates. Review of 1997 state reports, with correlation of measurement rates to birth cohort and provider numbers, public/private proportions, and vaccine distribution systems. Of the 9505 public clinics, 48% were measured; 4 states measured all clinics; 29 measured a majority. Measurement rates were highest for Health Department clinics (67%), lower for community/migrant health centers (39%), and lowest for other clinics (22%). Rates were highly correlated among categories of clinics (r>+0.308, P<.03), and the fewer the clinics, the higher the measurement rates (r = -0.351, P =. 01), but other factors were not significant. Of the 41,378 private practices, 6% were measured; no state measured all its practices; 1 measured a majority. Private practice measurement rates were not correlated to public clinic measurement rates or other factors examined. Of the 50,883 total providers, 14% were measured; no state measured all providers; 2 measured a majority. A trend toward higher measurement rates was found in states with fewer providers (r = -0. 266, P =.06). Three years after the congressional mandate, only a minority of public clinics and very few private practices had their immunization coverage measured. Greater efforts will be needed to assure implementation of the intervention. Arch Pediatr Adolesc Med. 2000;154:832-836

Microcomputer system of parallel measuring structure for period/frequency monitoring

Hardware implementing a method of period/frequency measurement, invented to increase the measurement speed, is described. An instantaneous frequency to be determined is calculated from the period measurement of an input signal. In order to obtain a high measurement rate a parallel structure is employed in the system hardware. The method can be applied in fast measurements of period and frequency, particularly in the low-frequency range. An example of design of a PC microcomputer system for monitoring the frequency of mains is presented. The measuring part of the system was implemented on an ISA extension card designed for the above purpose using simple TTL logic.

A systematic investigation on the use of time-dependent sensor signals in signal-processing techniques

Due to the lack of selectivity and separability of most common chemical sensors, the use of sensor arrays in combination with artificial neural network (ANN) signal processing is widely used. The time-dependent behaviour of gas sensors is one of the principal problems in signal-processing methods for sensor arrays. These time dependencies of semiconductor sensors can be classified into three main time domains: first, the rise time of the sensor after a sudden concentration change; secondly, the short-term drift after switching on; and finally, the long-term deterioration of the semiconductor material. An important improvement in the treatment of these time-dependent processes is the compensation of sensor rise time and short-term drift effects. The short-term drift of semiconductor sensors can be modelled and equalized by a preprocessing step. The rise-time effects can be reduced by measuring the sensor signals with a high measurement rate and training ANN's with these measurements. Preprocessing the sensor signal and applying the rise-time behaviour leads to an improvement of ANN generalization ability, and attains a minimum of prediction error after a minimum of time after gas exchange.

Accuracy aspects of DOA and angular velocity estimation in sensor array processing

A sensor array processing algorithm for joint estimation of the directions of arrival (DOAs) and the corresponding angular velocities is presented, together with the Cramer-Rao bound (CRB) of the problem. An embedded movement model circumvents the problems of biased estimates or high measurement rates that occur when conventional DOA estimation algorithms are applied to moving targets.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Exposure to soluble barium compounds: an interventional study in arc welders.

Soluble barium (Ba) compounds are well-known toxicants. Intoxications are mainly known in an acute form from casual or suicidal oral ingestion. No scientifically based data are available on possible health effects of inhalative exposure to soluble Ba salts at the workplace. Therefore, we investigated 18 welders in an interventional study over 1 week. They performed welding of Ba-containing stick electrodes and self-shielded flux cored wires under conditions similar to real working conditions. The welding fumes contained 31%-37% Ba, more than 90% of which was soluble in acids. Without appropriate preventive measures, a high rate of measurements exceeded the TLV values for total welding fumes of 5 mg/m3 and for soluble Ba of 0.5 mg/m3. The median fume concentrations were 13.2 mg/m3 in stick electrode welding and 12.3 mg/m3 in flux cored wire welding. The median Ba concentrations were 4.4 and 2.0 mg/m3 respectively. An integrated exhaust system built into the gun proved to be efficient in flux cored wire welding. The internal exposure to Ba reached median urine levels up to 101.7 micrograms/l (normal: below 20 micrograms/l) and median plasma concentrations of up to 24.7 micrograms/l (normal: below 8 micrograms/l). No health impact on the welders could be proven, but hypokalemia may have occurred as a result of the Ba exposure.

Automated flow injection determination of salicylates using Trinder reaction for clinical analysis, assays and dissolution studies of formulations

An automated flow-injection technique is described for salicylate (25-250 or 80-800 mg l(-1)), salicylamide (30-300 mg l(-1)), methylsalicylate (100-1000 mg l(-1)) and acetylsalicylic acid (after alkaline hydrolysis), based on their colour reaction with iron (III) in weak acid medium. The method was evaluated for the determination of salicylate in serum, the assay of the drugs in commercial formulations and automated dissolution studies of drug tablets. There were decreased interferences because of the short reaction time. The precision was good with RSD less than 1% in all cases. Recoveries of salicylate from spiked sera (100-1000 mg l(-1)) varied from 96.4-102.5% (mean 99.3%), and from spiked sample solutions of acetylsalicylic acid, 97.8-103.0% (mean 99.6%). The results of the analysis of commercial drug formulations obtained with the proposed method agreed well with the current USP and BP procedures, with differences of 0.4-1.5% (mean 0.8%). High measurement rates of 180 or 95 per hour were achieved using manifolds without and with predilution respectively.