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.
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.
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.
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.
This paper presents a method to digitally correct for static, analog circuit imperfections in a two-stage, 6th order, cascaded sigma–delta modulator. By adding a digital correction term to the output of the digital noise cancellation filter, the first stage parasitic quantization noise due to finite amplifier gain and C-ratio mismatches can be completely removed. This enables operation without significant degradation for amplifier gains as low as 400 at OSRs ranging from 16 to 24. Measurements have been conducted with a prototype circuit to verify the proposed error correction technique. The experimental results are in good agreement with the theoretical expressions and simulations.
The survey is intended to provide up-to-date information on the developments in thermometry involving the use of gaseous substances. The use of well specified thermodynamic states of condensed gases as fixed temperature points (2.2–220 K) is illustrated, and the sealed-cell method described as the most effective for their realization. Secondly, thermometric methods exploiting a pressure-temperature relationship are described. For the gaseous state, the developments in gas thermometry (1–300 K) are illustrated, not only for absolute thermometry, but also for interpolating thermometers (as required, e.g., by the ITS-90), and for simple and practical self-contained devices. Subsequently, in connection with condensed gases, developments in vapour-pressure thermometry are described.
A three layer feed-forward artificial neural network (ANN) was utilised to process the complex dependence of the absolute Seebeck coefficients (ASC’s) of pure palladium and platinum on their thermodynamic properties. The latter were computed using molecular dynamics (MD) simulations, which, together with experimental ASC’s data from the literature formed the training data for a neural network. A further test set was predicted at an rms of 0.3, enabling the interpolation of ASC’s at sixteen ITS-90 temperatures to be predicted. These ASC’s can be used to extend the response range of thermocouples.
The influence of a 90° mitre bend/reducer combination on the performance of two geometrically similar electromagnetic flowmeters has been investigated, the pair of electrodes for each meter being 7.667 diameters downstream of the reducer’s exit. At a distance of 1.667 diameters upstream from the electrode plane laser Doppler anemometry measurements show that the mean and root mean square velocity profiles are significantly fuller and skewed, in both the vertical and horizontal planes, especially for the lowest flow-rate. The results show that the percentage meter error, for the higher flow-rates was at or below 1%, this figure increases to between 2 and 4% for the lower flow-rates investigated.
Absolute distance interferometry, which has been investigated and developed in various research laboratories worldwide and which can be regarded as an extension of conventional interferometry, offers the advantages of high resolution coupled with the fact that measurement operations suspended by an interruption of the laser light beam are resumed as soon as the shading disappears. Additional benefits accrue from the immediate availability of a distance value when the facility is activated and from the fact that point measuring operations can be conducted without complicated linear stages. An absolute interferometrical distance measurement technique using a tunable semiconductor laser which, by virtue of its external cavity, has extremely small linewidth and, therefore, considerable coherence length, is discussed in this contribution. The application of this technique has already permitted a relative measurement uncertainty of 10−6 to be achieved over a distance of 40 m.
In the present study, a new in situ absolute calibration method for a displacement sensor is proposed, and a calibration system is developed. This new method is capable of determining not only the linearity error but also the mean sensitivity (inclination of linear calibration line) on the base of the wavelength. The new measurement system consists of a compact laser interferometer and a previously developed in situ calibration system. The laser interferometer is used only to determine the necessary displacement shift quantity with an integer multiple of half wavelengths of the laser light source. Using this known displacement shift quantity, the mean sensitivity and the linearity error of a displacement sensor can be determined absolutely. The accuracy of the proposed method depends only on the stabilities of the calibrated displacement sensor itself and the wavelength of the laser light source. A capacitance-type non-contact displacement sensor was calibrated successfully to the limit of stability of this sensor, which is determined from the signal-to-noise ratio.
The use of ceramic materials in scientific research and industry has been growing in the past few years. The scope of this article is to describe the specification, design and calibration of a far-infrared pyrometer suited to measure surface temperatures on semitransparent materials such as alumina and silica and on coated composite materials. The specific problem being discussed is that the materials to be tested are heated by means of a plasma jet through which the temperature has to be measured.
It is well accepted within the international research community that there is a requirement for a high resolution facility for carrying out multi-dimensional moisture content measurements under transient conditions. This investigative tool should be capable of accommodating material samples large enough to incorporate the various macroscopic features, including mortar joints and material interfaces, which are known to exert a significant influence on moisture transport within building envelopes. Such a tool, based on the principle of X-ray absorption, is being developed at Glasgow Caledonian University. A brief description of the facility is given here, together with modifications which allow the imaging of samples to be generated using computer-aided tomography. Also reported are the results of liquid water diffusivity experiments carried out on four masonry materials. These formed part of the calibration and validation procedure. The test data, describing the evolution of moisture content with time at various locations from a wetting plane, were collapsed to single curves using the Boltzmann transformation. These curves were then fitted to yield liquid diffusivity for application within moisture simulation models. The relationships derived are based on a novel simplified approach, which is easier to apply than the complicated procedures generally adopted hitherto.
A tight control of the level of blood glucose is known to reduce the long-term complications of diabetic patients. A non-invasive measurement method suitable for home use would allow a more accurate and frequent control of glucose level, along with reducing the long-term health care costs of diabetic patients and improving their quality of life. In clinical use, the non-invasive method would be suitable for several applications, such as rapid monitoring of glucose levels in emergency rooms [G. Cote, J. Clin. Engrg. 22 (4) (1997) 253–259]. In this work, the potential of near infrared (NIR) spectroscopy as a non-invasive method has been evaluated on the basis of theoretical considerations and measurements on water–glucose solutions and a test person. The partial least squares (PLS) algorithm was used in calibration. The standard deviation of the error of prediction was 0.97 and 1.14 mmol/l for measurements from water–glucose solutions and the test person respectively.
A mixed electronic system has been designed to measure the active, apparent and reactive energies delivered to a load in a single-phase AC voltage line. For this purpose a smart sensor (ADE7753 from Analog Devices) was used. A magnetoresistance sensor is used as a current transducer and it is constant current biased by a generalized impedance converter. The magnetoresistance sensor technology provides direct isolation from the mains voltage and ferrite cores are not needed like Hall counterparts. All the measurements provided by the ADE7753 are read through the parallel port of the computer using a LabView application, which will process and present the readings to the user.
The need for accelerated curing of concrete in precast civil engineering components is discussed, and the techniques available to achieve this are presented, with particular emphasis on the use of direct electrical conduction.The principles of the design of automatic laboratory equipment to investigate accelerated curing of concrete using this technique are described, and results are presented for trial experiments, including an assessment of the input energy necessary to achieve a particular degree of curing in a given time.
In several applications one or more accelerometers are used to estimate position, which is derived by double integration of the acceleration measurements. An experimental method to calibrate the positional errors due to noise for an accelerometer has already been developed. In this paper, a theoretical formalism for this calibration method is derived, which is based on modelling the acceleration measurements as filtered noise. The effects of numerical integration are included in the model. Two accelerometers, with different noise ratings, are chosen for study. It is found that the theoretical model gives good quantitative agreement between theory and experiment for the variation of positional errors with integration time. The causes of the discrepancies between the theoretical and experimentally found results are discussed and suggestions are made for further research.
In this paper two digital filters are applied to elaborate acceleration data acquired from two accelerometers fixed in a lift frame during safety gears tests. The experimental tests consist in free falls of a test lift car and the subsequent gripping phases initiated by the safety gears activation due to over-speed condition. Unfortunately, the reliability of acceleration data is heavily impaired by measurement noise, which needs to be suppressed to the largest extent possible in order to use the data for comfort evaluation. To this end, two classes of digital filters are tested: the Savitzky–Golay and the Butterworth filters. This choice is motivated by the key features of these filters, including their computational simplicity and high suitability to represent time varying features in acceleration measurements. A tuning procedure is proposed for these filters, such that the measurement noise corrupting the experimental data is maximally dumped.
In this paper we describe the implementation and test of an optical fiber based accelerometer with cross axis insensitivity. The accelerometer uses two matching fiber Bragg gratings which are also responsible by the demodulation of the wavelength encoded information. The accelerometer was tested in a reinforced concrete slab, of a 3-storey building located at the University of Aveiro, Portugal. A maximum error of 0.25% for the slab eigenfrequencies was obtained when compared with the values acquired by an electronic sensor.
This paper describes the design and development of a accelerometer-based thin flat balance system for measuring aerodynamic forces on typical flight configurations in impulse facilities. The balance system is used to measure the axial force on a blunt-nosed triangular plate flying at Mach 5.75 in IISc hypersonic shock tunnel HST2 with a test flow duration of 800 μs. The model and the balance system are supported by rubber bushes, which leads to minimally restrained free floating conditions of the model in the test section during the flow duration. Exhaustive 3D finite element simulations are carried out to select appropriate rubber material. The measured and simulated values of axial force match very well with the theoretical values predicted using Newtonian theory at moderate specific enthalpy levels of the test gas. In addition, the importance of implementing the 3D-FEM analyses in design study of the accelerometer balance system has been highlighted by comparing the results of axi-symmetric modeling with 3D modeling.
MEMS accelerometers have received attention owing to their low cost and small size. Accurate vibration measurements of both amplitude and phase, in the measurement frequency range, are important for reliable vibration analysis. However, a number of MEMS accelerometers from different manufacturers show some deviation, in amplitude and phase, when examined using controlled vibration laboratory measurements.This paper presents a method to improve MEMS accelerometers performance. Through the laboratory measurements, a characteristic function (CF) for a typical MEMS accelerometer has been calculated, with reference to a standard accelerometer. Using the CF, a filter has been designed for the MEMS accelerometer, which corrects for amplitude and phase deviation.
A signal processing method for identifying the input–output behavior of accelerometers is developed. The method is based on the state-space description of the relationship between input, noise and output signals. The accelerometer is modeled as a one-degree-of-freedom system. The acceleration input signal is derived from the interferometrically measured displacement signal by a subroutine for the low-noise estimate of the input acceleration. For observed sequences of input–output data, the parameters of the transfer function of the accelerometer are estimated by minimizing the prediction error sequence of the state-space model. The identification procedure developed was applied to accelerometer input–output data with peak values ranging from about 104 to 5 × 104 m/s2 furnished by a shock acceleration standard device. The estimated transfer function characterizes the input–output behavior of the accelerometer in the time and frequency domain and allows to determine the acceleration output signals for non-stationary input signals, for example, the peak values in primary shock calibrations.
Knowledge of drag force is an important design parameter in aerodynamics. Measurement of aerodynamic forces at hypersonic speed is a challenge and usually ground test facilities like shock tunnels are used to carry out such tests. Accelerometer based force balances are commonly employed for measuring aerodynamic drag around bodies in hypersonic shock tunnels. In this study, we present an analysis of the effect of model material on the performance of an accelerometer balance used for measurement of drag in impulse facilities. From the experimental studies performed on models constructed out of Bakelite HYLEM and Aluminum, it is clear that the rigid body assumption does not hold good during the short testing duration available in shock tunnels. This is notwithstanding the fact that the rubber bush used for supporting the model allows unconstrained motion of the model during the short testing time available in the shock tunnel. The vibrations induced in the model on impact loading in the shock tunnel are damped out in metallic model, resulting in a smooth acceleration signal, while the signal become noisy and non-linear when we use non-isotropic materials like Bakelite HYLEM. This also implies that careful analysis and proper data reduction methodologies are necessary for measuring aerodynamic drag for non-metallic models in shock tunnels. The results from the drag measurements carried out using a 60° half angle blunt cone is given in the present analysis.
This investigation concerns the performance of different kinds of strain gauges and accelerometers in a high-frequency shock environment. The experimental method is based on the Hopkinson bar, which was designed for two different types of waves, i.e. a longitudinal monomode pulse wave mainly for calibration purposes and a longitudinal/radial multimode wave for operational tests with superimposed ultrasonic noise. The Hopkinson bar is used as a model representation for real test objects. Foil strain gauges have proved to be well suited for shock measurements if the strain levels are sufficiently high. Polyvinylidene fluoride (PVDF) gauges are the best choice for low strain levels due to their excellent signal-to-noise ratio. The application of accelerometers requires careful selection of the sensor type with respect to its range, natural frequency, damping, mass, cross sensitivity and stiffness of fixture. The results show that the interpretation of recorded acceleration signals is often difficult.
A technique for the systematic design of fault-tolerant automatic measurement systems based on ‘analytical redundancy’ relationships is proposed. Starting from the user requirements in terms of quantities to be monitored and of number and type of faults to be detected, isolated, and accommodated, the proposed technique suggests the number and location of the sensors to be used in the measurement system to be designed or the modifications needed in an existing measurement system for satisfying the user requirements. The peculiarities of this technique were highlighted by applying it to some real measurement stations.
A microdimension measurement system, using one-dimensional CCD as the sensor, was developed for measuring thin wire or slit. The principle of measurement is based on Fraunhofer's diffraction. The system performs data processing of the diffraction pattern by using filtering and curve-fitting, by which the measuring accuracy was extremely improved. The measuring range of this system is from 20 μm to 200 μm. The total measuring uncertainty is less than 0.04 μm and the repeatability of measurements is less than 0.011 μm. Moreover, experimental results indicate that the system is applicable to vibrating objects as well.
Measurement of carbon dioxide has great clinical significance during mechanical ventilation, in the adjustment of ventilatory parameters and detection of respiratory complications. The main objective is to investigate the correlation between end-tidal carbon dioxide pressure (PetCO2) and partial pressure of arterial carbon dioxide (PaCO2) measured at 37 °C and corrected for body temperature in patients with thermal instability. Altogether, 110 measurements were analyzed, and the correlation was statistically more significant for corrected temperature than measured PaCO2. The difference between corrected and uncorrected PaCO2 varies from 3% per °C for hypothermic patients and 6.5% per °C for hiperthermic patients. The difference between PaCO2 measured and PetCO2 (Pa–etCO2) resulted in an increase for all temperature degree, reaching a maximum difference of 9 torr. In contrast, Pa–etCO2 has little variation when corrected PaCO2 was used for calculation around −2.1 to 3.1 torr for hypo and hiperthermic patients. Thus, PetCO2 reflects temperature corrected PaCO2 more adequately than measured PaCO2.
The use of laser Doppler velocimeters in the analysis of in-plane motion of a solid body is spreading both in the scientific research and in the industrial experimentation fields. The applicability and accuracy of this measurement technique depend on the conditions in which the system operates: the level of the signal available, the characteristics of the surface observed, the environmental conditions, the presence of other shifts in addition to the ones pointed out, etc. This is the subject of this analysis carried out through a comparison between an axial vibrometer in conditions of ideal operation and a tangential vibrometer operating on various surface states. The experimental results have been supported by a theoretic modelling of the interaction between this measuring system and the measurand, thereby providing a rational description of the phenomena observed. This study has made it possible to verify the interfering inputs due to the various operative conditions and the chance of extending the use of the measurement system also to cases in which the applications of the technique proves to be difficult.
A short overview of the principles of probe heads of coordinate measuring machines. It si shown that only probe heads with two or three degrees of freedom, associated transducers for measuring the spatial movement of the probe ball, and linearity between measuring force, deflection and transducer signals allow to measure coordinates in space without errors caused by deflection of the probe stylus and inclined workspiece touching. In order to get a full error-free function the probe head must be calibrated by means of algorithms using all degrees of freedom simultaneously.
The paper concerns the problem of the accuracy of multiperiod counters working under dynamic conditions, i.e. when subsequent periods are changing. The same problem appears when the fluctuating values of a measurand are converted to a frequency signal, and its period instead of the frequency is measured. It is shown that under dynamic conditions two additional errors should be taken into consideration. One of them is a random error caused by the specific sampling process, while the second one, called dynamic error, is systematic and may be reduced by introducing a corrective value Tcor. In some cases the magnitude of the dynamic error is much greater than all other errors of the period counter.