Measurement

A neural approach to modeling measurement devices is presented. This approach allows the usual components of a measurement apparatus (transducers, filters, amplifiers, analog-to-digital converters, etc.) to be easily modeled by means of suitably trained Artificial Neural Networks. Two applications regarding analog and mixed analog/digital devices are reported, highlighting the peculiarity of this approach and the accuracy obtainable

The magnetic flux leakage (MFL) method has established itself as the most widely used in-line inspection technique for the evaluation of gas and oil pipelines. The MFL data obtained from seamless pipeline inspection is usually contaminated by the seamless pipe noise (SPN). SPN can in some cases completely mask MFL signals from certain type of defects, and therefore considerably reduces the detectability of the defect signals. This paper presents a modified wavelet transform domain adaptive FIR filtering algorithm for removing the SPN in the MFL data. The proposed algorithm can effectively cancel the SPN in the MFL data with high correlation and therefore improves the detectability of the defect signals with relatively low correlation by employing the different correlation properties of SPN and defect signals. Results from application of the modified algorithm to the MFL data from field tests show that the modified algorithm has good performance and considerably improves the detectability of the defect signals in the MFL data

The determination of the stationary transfer function of an ADC using an automated test system and employing the histogram test using, however, Gaussian noise as the stimulus signal, is presented. This transfer function is used to derive merit figures like SNDR, THD and effective number of bits

Direct Generation of Sinusoids using an Arbitrary Waveform Generator is a common synthesis technique. Generating an arbitrary frequency has generally been implemented by synthesizing a master clock frequency with techniques, which can introduce jitter. A method of generating a frequency to an arbitrary accuracy using the mathematics of continuing fractions is described

This paper proposed and implemented an efficient and reliable backup scheme for bridge monitoring system. It is mainly using the wireless sensor network (WSN) to gather the related environment parameters, and transmitting the numerical data to the gateway through multiple-hop relay, and then it further stores data in the back-end database for the professional monitoring staffs to analyze and study. The proposed backup scheme could to ameliorate the inconvenience to add or remove sensor nodes in an existing wired bridge monitoring network. Final, the feasibility of the proposed scheme is verified by experimental results.

A system approach is outlined and applied to electrical measurements. The essential idea of the system approach to electrical measurements is uniform treatment of measurement problems and/or instruments, which can be considered as special cases of a system whose functions are performed via signal processing. The notions of measuring system, its calibration and measurand reconstruction are interpreted on the basis of this approach. A design methodology and selected problems of applying VLSI technology to measuring system design are discussed

Monitoring systems for this part of a rotating machine are difficult to elaborate. Effectively the problem is to transmit this information from the rotating rotor to the fixed stator, given the inherent presence of the electromagnetic field. In this paper we propose a new measurement device using optical fiber for all sensor types. This device is not subject to electrical or magnetic interference. Application for thermal monitoring has been tested by detecting a rotor fault in the cage of an asynchronous motor

The 1.5 μm ytterbium–erbium laser was extensively investigated in terms of its intensity and frequency noise characteristics. The energy transfer process between Yb and Er ions in the codoped active material was shown to reduce substantially the intensity noise induced by pump power fluctuations. To further suppress the intensity noise, a suitable control loop acting on the injection current of the pump laser diode was employed, providing for a 30-dB reduction of the relaxation oscillation peak. Some high-resolution laser spectroscopy measurements have been performed on the acetylene molecule by means of the tunable Yb–Er microlaser. Frequency locking and stabilization was achieved by both the fringe-side locking technique and the FM side-band technique, using different rovibrational lines of the C2H2. The beat note between two independently stabilized diode-pumped Yb–Er:glass lasers, operating at 1534.097 nm wavelength, yielded a long-term frequency stability of 170 kHz with an Allan standard deviation below 10−10 for integration times between 10 ms and 1 s.

This paper describes a measurement method developed at National Institute of metrological Research (INRIM) to calibrate picoammeters in dc current from 100 pA to 100 nA. The current source is based on a traceable to the dc resistance national standard 10 × 100 MΩ Hamon resistor developed at INRIM and on a traceable to the dc voltage national standard high precision dc voltage calibrator. The expanded uncertainties of the method for the calibration of picoammeters span from 9.4 × 10−4 for the gain of a picoammeter at 100 pA to 4.0 × 10−4 for the gain at 100 nA. A detailed uncertainties budget at 10 nA level and the results of a comparison with a different technique are also reported.

There has been a recent interest on the performance of amplitude estimation employing a coherently sampled sinusoidal model to noisy measurements. In [F. Correa Alegria, Bias of amplitude estimation using three-parameter sine fitting in the presence of additive noise, Measurement 42 (2009) 748–756.], several issues regarding the bias of the amplitude estimate were studied. In this work, the results are generalized to include a description of the distribution of the amplitude estimate, with explicit results on bias and variance as by-products. Simple closed form expressions for bias and variance are derived. It is shown that the amplitude estimate in finite samples obeys a Rician distribution. The biased amplitude estimator is also shown to beat all unbiased estimators in terms of mean square error, in a wide spread of scenarios.

The behaviour in air of K and N thermocouples of the bare-wire and metal-sheath types is examined in the 0°C to 850°C range. Considered are emf variations due to short-term ordering phenomena, which occur mostly in K thermocouples, as well as hysteresis. Suitable stabilization cycles can achieve improvement of the reproducibility. The paper gives also data concerning the S-type thermocouples used in industrial laboratories and SIT (Italian Calibration Service) calibration centres. In fact, although the platinum resistance thermometer and monochromatic pyrometer are the primary standards in the 600°C to 1060°C range according to ITS-90, the S-type thermocouple is still used as a reference in calibrations at the industrial level considering its low cost and easy use in these measurements. A calibration from time to time is necessary to verify the conformity to the reference tables and reproducibility of the S-type thermocouples to achieve a total uncertainty better than ± 0.2°C.

Test Access Port and Boundary-Scan Architecture, IEEE Std. 1149.1, was developed to ease the test of printed circuit board assemblies (PCBAs). The development of packaging technology and the increasing functionality of a circuit have made traditional testing methods, such as in-circuit tests and functional testing through edge connectors much more difficult or even impossible. Mixed-Signal Test Bus, IEEE Std. 1149.4, which is a further development of IEEE Std. 1149.1 has been developed to enable the testing of analog components and analog interconnects on PCBAs.IEEE Std. 1149.4 compliant circuits contain an analog bus and analog switches. Techniques applicable to the measurement of impedances via IEEE Std. 1149.4 compliant circuits are presented. A filter has been tested and the results are promising. It has been shown by both measurement and simulation that switching impedances can be managed in such a manner that the influence of deviations from their nominal value can be estimated.

In this paper, we propose a methodology to discriminate electro-optical failure signatures related to an optical alignment drift in the laser module in comparison of those related to the gradual change of electro-optical parameters of the laser diode. A specific test bench with temperature dependence has been developed to monitor P(I), I(V) and L(λ) of 15 DCBH InGaAsP/InP 1310-nm Fabry-Perot laser modules and has allowed to extract three main failure signatures after 300 thermal cycles. A study of experimental I(V) curves from reference laser modules has resulted in the development of a DC electrical circuit with a non-linear element tunnel diode Dtunnel contributing to a better understanding of current distribution parallel paths inside the laser diode. After accelerated ageing tests, two signatures are related to an gradual change of both electrical and optical parameters conducting to identify failure mechanisms in the laser diode and discrimination of failures zone was improved by a reverse bias I(V) measurement. The third signature has shown an optical gradual change without any modification of the threshold current or ideality factor. We also demonstrate the strong interest of L(λ) measurements complementary to I(V) and P(I) characteristics.

In this paper a bandpass MASH (multi-stage noise shaping) sigma-delta (ΣΔ) modulator is presented. A SNR (signal to noise ratio) of at least 85 dB (equivalent to a resolution of 14 bits) has been achieved over a 5 MHz band around an intermediate frequency (IF) of 20 MHz using a clock frequency of 80 MHz. This performance is obtained using a sixth order bandpass ΣΔ modulator followed by a 10 bit pipeline converter. The proposed circuit has been extensively simulated, both at behavioral and at circuit level, and results are reported.

A short survey of technologies proposed and implemented so far for landmine detection is given. A laboratory prototype device intended for RDX and HMX explosive detection in landmines by means of 14N-NQR (nuclear quadrupole resonance) spectroscopy is described. This NQR based landmine detector is essentially a fully automated and computer controlled FT-NQR spectrometer equipped with a planar r.f. measure coil. The temperature dependencies of NQR frequencies νQ(T) in RDX and HMX in the temperature range of practical interest for explosive detection were measured. Final testing of the device has been carried out on samples of sodium nitrite (NaNO2) which had to be used to simulate real landmines in order to obey the safety regulations. Experimentally optimized SORC (strong off-resonance comb) multi-pulse sequence were used for optimum NQR signal. The time of detection was 30 and 90 s for sodium nitrite simulants buried in depths of 7 and 10 cm under ground, respectively. The sensitivity of detection was limited mostly by the external r.f. interferences, both man-made and naturally occurring, which enter the NQR detection system through the unshielded measure coil. Possible means to circumvent these limitations are also discussed.

The purpose of this paper is to present the results of magnetic induction measurements recorded at various high voltage centers of the Greek network. The implications of these results are also discussed. The high voltage centers are located in the Athens area and this paper also deals specifically with a high voltage center of 150/20 kV situated within the city center. The total of all recorded measurements from all centers indicate that magnetic field values are lower than the internationally accepted reference (safety) limits.

Different heat treatment processes can be applied on the spring element of a force transducer in order to obtain good and satisfactory performance. The study covers the attempts of different heat treatments on spring element using 17-4PH precipitation hardened stainless steel, which is regarded as one of the best and popular spring materials for force sensor applications. Heat treatments named as H900, H925, H1025, H1150 and S450 was applied, and different hardness values were reached. Especially, S450 heat treatment process was improved in this study. It was observed that heat treatments influenced the transducer performance, particularly hysteresis behaviour point of view. The results have shown that; hysteresis characteristics were improved with increasing hardness and sub-zero treatment process.

An endless supply of electricity is taken for granted in today’s world of commerce and business. Our dependence on a continuous supply of power, drives the search and development of reliable methods for the preventive diagnosis and maintenance of transformers.This paper primarily refers to measurements of insulating resistance in distribution transformers, at several temperatures, and thereafter to calculations of the thermal coefficient of the transformers. It overhauls the above characteristic magnitudes of 24 distribution transformers and indicates the observations and comments on ageing and remnant life of the insulation system of the transformers. A method for transformer life cycle prediction is suggested.

In this paper we present an Earth magnetic field measurement system and an automated acquisition setup to characterize it. The measurement system consists of a fluxgate sensor and an integrated front-end circuit, both realized in CMOS technology. The couple of orthogonal axes of the sensor makes the system suitable for realizing an electronic compass device. Indeed, we can measure not only the amplitude of the Earth magnetic field (whose full-scale value is of the order of 60 μT), but also its direction. The complete measurement system achieves a maximum angular error of 1.5° in the measurement of the Earth magnetic field direction. Furthermore, an acquisition setup was developed to evaluate the measurement system performance. It consists of a precision mechanical plastic structure, in tower form, a microcontroller-based interface circuit, that provides a digital output through an RS232 serial interface, a PC software suitably developed to post-process the data from the acquisition system and a couple of Helmholtz coils to evaluate the linearity of the system. This setup allows us to perform a completely automated and numerically controlled characterization of the measurement system.

The 3D theoretical model of a touch trigger probes pretravel is experimentally verified. A new method applying a low force high resolution displacement transducer is proposed to measure a probe pretravel in XYZ space. Experiments are carried out for both one and two stage types of probes. 3D surfaces of the probe pretravel are collected. Statistical regression and variance methods are applied for experimental data analysis. Good agreement with theoretical approach presented in part I of the paper is obtained. The investigations reveal that testing probes only in the plane perpendicular to its axis (which is a typical procedure so far) cannot detect the most significant probe functioning errors. Study of the probe hysteresis is performed. It is shown that parameters used so far like instability and repeatability of the pretravel are not sufficient for the full description of the accuracy of touch trigger probes. This applies particularly to two stage devices. Both the theoretical analysis and the experimental studies pointed at the hysteresis of the triggering point being the main source of probe errors.

Coordinate measuring machines (CMM) are universal devices for geometrical quality inspection of workpieces in manufacturing. But conventional CMMs are very large, expensive and very slow because of the point-by-point mode, they require a specially trained operator and exquisite environmental control. A novel CMM consisting of only one linear guideway and two linkages as known from Scara robots is described. It is manually operated in scanning mode with up to 400 measuring points per second. The high accuracy of the system has been reached by the precise design, the 3-D analog probe and force sensor, a novel calibration system for determining the linkage parameters as well as powerful correction of geometric, cinematic and deformation errors. Thermal errors are reduced to a great extent by carbon fibre and ceramics. The overall accuracy of the system is about 5 μm. The software contains powerful models for data validation and error correction, automatic detection of geometric elements, evaluation of form profiles as well as for calibration and self testing.

New 3D model of the inaccuracy of a touch trigger probe used to collect coordinates of a measured object by coordinate measuring machine (CMM) is proposed. The analysis is performed both for one and two stage types of probes. The influence of a stylus length and diameter, a spring force and direction of a contact point approach are taken into consideration. The effects of frictional interaction between the stylus ball and a measured surface are also taken into consideration. The theoretical analysis of a tough trigger probe hysteresis is presented. Finally a computer simulation of mathematical modeling in the XYZ space is shown.

A three-dimensional flow visualisation technique has been developed and used to measure the three mean velocity components, the associated turbulence levels and the kinetic energy of turbulence. The experiment involved an inclined 45° circular jet in a rectangular enclosure. The technique makes use of three light sheets of different colour and a standard CCD colour camera interfaced to a video recorder and a PC. The analysis algorithm relies on determining the length and colour of the resulting tri-colour streaklines to provide rapid, field-wide, qualitative and quantitative velocity information which is not subject to ambiguity stemming from varying particle concentration fields. Characteristic results show good agreement with 3D-PIV data. The purpose of the experiment was the calibration of the technique rather than the study of the flow, hence the results reported should only be considered as an indicative for the study of the jet flow.

Kinematic touch trigger probes are widely used with coordinate measuring machines (CMMs) to register the position of their axes when contact between the probe tip and the object occurs. However, much interest has been devoted recently to the compensation of systematic errors produced by this type of probe due to the pre-travel variation. This paper proposes an experimental means of characterising the pre-travel behaviour of the probe system in 3D and independently of the CMM error sources. On the basis of these results, a 3D error correction model is proposed which determines the actual pre-travel. The model only requires a small number of parameters for its definition. It is based on a sliding contact between the probe tip and the object. A method for updating the model from CMM measurements on the re-qualification sphere is then presented. The effect of the stylus length and of the tilt of the probe axis relative to gravity are also studied. Experimental validations show that the simple correction model provides an effective correction of the probe systematic error.

This paper describes the design and evaluation of a novel optical instrumentation system that has been developed for the on-line continuous measurement of temperature distribution in a furnace. The system comprises optical filters, a CCD camera, a frame-grabber and associated software. Based on the two-colour method, the average temperature of the flame field is calculated from the ratio of averaged grey levels of the two images alternatively captured at two different wavelengths. Accordingly, a pseudo-instantaneous temperature distribution is obtained from a single-wavelength image and presented by pseudo-colour. Experimental results obtained from a 500-kW model furnace show that the temperature distribution ranged from 1331 to 1606°C for coal-fired flames and from 1156 to 1358°C for gas-fired flames. A continuous monitoring of the temperature distribution in the furnace has also been performed over a period of 100 min. A comparison between the results measured by the system and those from a conventional pyrometer demonstrates that the system is capable of measuring the temperature distribution with a reasonable accuracy.