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Next generation AT-cut quartz crystal sensing devices
Vojko Matko, 2011, izvirni znanstveni članek

Opis: Generally, AT-cut quartz crystals have a limited scope of use when it comes to high-precision measurement of very small impedance changes due to their nonlinear frequency-temperature characteristics in the range between 0 °C and 50 °C. The new method improving quartz oscillator frequency-temperature characteristic compensation is switching between two impedance loads. By modifying the oscillator circuit with two logic switches and two impedance loads, the oscillator can switch oscillation between two resonance frequencies. The difference in resonance frequencies compensates the frequency-temperature characteristics influence as well as the influence of of fset and quartz crystal ageing. The experimental results show that the new approach using the switching method highly improves second-to-second frequency stability from +/-0.125 Hz to +/-0.00001 Hz and minute-to-minute frequency stability from 0.1 Hz to 0.0001 Hz, which makes the high-precision measurement of aF and fH changes possible.
Ključne besede: quartz crystal, switching oscillating method, temperature characteristic compensation
Objavljeno: 22.06.2017; Ogledov: 124; Prenosov: 7
.pdf Celotno besedilo (382,71 KB)

New quartz oscillator switching method for nano-Henry range inductance measurements
Vojko Matko, Karel Jezernik, 2012, izvirni znanstveni članek

Opis: This article introduces a new method for nano-Henry inductance measurements atthe frequency of 4.999 MHz with a single quartz crystal oscillating in the switching oscillating circuit. The real novelty of this method, however, lies in a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 0 °C and 50 °C through a switching method which compensates for the crystalćs natural temperature characteristics. This allows for the compensation of any influences on the crystal such as the compensation of the non-linear temperature characteristicsand the ageing of both the crystal and other oscillating circuit elements, as well as the reduction of the output frequency measurementerrors with the help of an additional reference frequency. The experimental results show that the switching method greatly improves the measurement of small inductance changes in the range between H and nH, allowing as a result high-precision measurements (~0.35 fH) in this range.
Ključne besede: quartz crystal, switching oscillating method, nano-Henry range measurement
Objavljeno: 22.06.2017; Ogledov: 85; Prenosov: 5
.pdf Celotno besedilo (872,06 KB)

MOS-FET as a current sensor in power electronics converters
Rok Pajer, Miro Milanovič, Miran Rodič, Branko Premzel, 2015, izvirni znanstveni članek

Opis: This paper presents a current sensing principle appropriate for use in power electronics’ converters. This current measurement principle has been developed for metal oxide semiconductor field effect transistor (MOS-FET) and is based on UDS voltage measurement. In practice, shunt resistors and Hall effect sensors are usually used for these purposes, but the presented principle has many advantages. There is no need for additional circuit elements within high current paths, causing parasitic inductances and increased production complexity. The temperature dependence of MOS-FETs conductive resistance RDS−ON is considered in order to achieve the appropriate measurement accuracy. The “MOS-FET sensor” is also accompanied by a signal acquisition electronics circuit with an appropriate frequency bandwidth. The obtained analogue signal is therefore interposed to an A-D converter for further data acquisition. In order to achieve sufficient accuracy, a temperature compensation and appropriate approximation is used (RDS−ON = RDS−ON(Vj)). The MOS-FET sensor is calibrated according to a reference sensor based on the Hall-effect principle. The program algorithm is executed on 32-bit ARM M4 MCU, STM32F407.
Ključne besede: power electronics, converters, MOS-FET, current measurement, thermal model
Objavljeno: 22.06.2017; Ogledov: 130; Prenosov: 11
.pdf Celotno besedilo (1,32 MB)

Monitoring the evaporation of fluids from fiber-optic micro-cell cavities
Eyal Preter, Borut Preložnik, Vlada Artel, Chaim Sukenik, Denis Đonlagić, Avi Zadok, 2013, izvirni znanstveni članek

Opis: Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identificationof fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.
Ključne besede: fiber-optic sensors, opto-fluidics, evaporation monitoring, optical micro-cells, fiber cavities, droplet analysis
Objavljeno: 22.06.2017; Ogledov: 53; Prenosov: 5
.pdf Celotno besedilo (551,58 KB)

Major improvements of quartz crystal pulling sensitivity and linearity using series reactance
Vojko Matko, Riko Šafarič, 2009, izvirni znanstveni članek

Opis: This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF andfrequencies in the range of 3.5 to 21 MHz. The research describes high quartz pullability and linearity by varying the load capacitance. The paper also gives impedance circuits for crystal unit (3.5 MHz) together with load capacitance and compensation reactance. The experimental results show that thenew approach using compensation method of quartz crystal connected in series reactance increases the frequency pulling range by *25 to *100 depending on the type of oscillator and compensation factor k in the temperature range of 10 to 40 °C.
Ključne besede: quartz crystal, pulling range, pulling linearity
Objavljeno: 22.06.2017; Ogledov: 56; Prenosov: 5
.pdf Celotno besedilo (256,09 KB)

High resolution switching mode inductance-to-frequency converter with temperature compensation
Vojko Matko, Miro Milanovič, 2014, izvirni znanstveni članek

Opis: This article proposes a novel method for the temperature-compensated inductance-to-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit to achieve better temperature stability of the converter. The novelty of this method lies in the switching-mode converter, the use of additionally connected impedances in parallel to the shunt capacitances of the quartz crystal, and two inductances in series to the quartz crystal. This brings a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 10 and 40 °C. The oscillator switching method and the switching impedances connected to the quartz crystal do not only compensate for the crystalʼs natural temperature characteristics but also any other influences on the crystal such as ageing as well as from other oscillating circuit elements. In addition, the method also improves frequency sensitivity in inductance measurements. The experimental results show that through high temperature compensation improvement of the quartz crystal characteristics, this switching method theoretically enables a 2 pH resolution. It converts inductance to frequency in the range of 85-100 nH to 2-560 kHz.
Ključne besede: inductance-to-frequency, switching methods, dynamic temperature compensation of circuit elements, precision metrology
Objavljeno: 22.06.2017; Ogledov: 56; Prenosov: 7
.pdf Celotno besedilo (2,22 MB)

Greatly improved small inductance measurement using quartz crystal parasitic capacitance compensation
Vojko Matko, Karel Jezernik, 2010, izvirni znanstveni članek

Opis: Generally, quartz crystal inductance frequency pulling in oscillators is very low and therefore is not often used in practice. The new method of improving frequencypullability uses inductance to compensate for quartz stray capacitances. To this end, a special AT fundamental quartz crystal working near the antiresonance frequency is selected. By modifying its equivalent circuit with load inductance and series tuning capacitance, the magnetic sensing of the circuit can be highly improved. The experimental results show that the new approach using the quartz crystal stray capacitance compensation method increases the frequency pulling range by x 300 depending on the type of oscillator, making possible the measurement of nano-magnetic changes.
Ključne besede: quartz crystal, magnetic pulling, parasitic capacitance compensation
Objavljeno: 22.06.2017; Ogledov: 67; Prenosov: 4
.pdf Celotno besedilo (145,07 KB)

Finite element modelling of a field-sensed magnetic suspended system for accurate proximity measurement based on a sensor fusion algorithm with Unscented Kalman Filter
Amor Chowdhury, Andrej Sarjaš, 2016, izvirni znanstveni članek

Opis: The presented paper describes accurate distance measurement for a field-sensed magnetic suspension system. The proximity measurement is based on a Hall effect sensor. The proximity sensor is installed directly on the lower surface of the electro-magnet, which means that it is very sensitive to external magnetic influences and disturbances. External disturbances interfere with the information signal and reduce the usability and reliability of the proximity measurements and, consequently, the whole application operation. A sensor fusion algorithm is deployed for the aforementioned reasons. The sensor fusion algorithm is based on the Unscented Kalman Filter, where a nonlinear dynamic model was derived with the Finite Element Modelling approach. The advantage of such modelling is a more accurate dynamic model parameter estimation, especially in the case when the real structure, materials and dimensions of the real-time application are known. The novelty of the paper is the design of a compact electro-magnetic actuator with a built-in low cost proximity sensor for accurate proximity measurement of the magnetic object. The paper successively presents a modelling procedure with the finite element method, design and parameter settings of a sensor fusion algorithm with Unscented Kalman Filter and, finally, the implementation procedure and results of real-time operation.
Ključne besede: accurate proximity measurement, sensor fusion algorithm, Unscented Kalman Filter, finite element modelling
Objavljeno: 22.06.2017; Ogledov: 114; Prenosov: 8
.pdf Celotno besedilo (9,23 MB)

Fiber-optic sensors for measurements of torsion, twist and rotation
Vedran Budinski, Denis Đonlagić, 2017, pregledni znanstveni članek

Opis: Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.
Ključne besede: fiber optic sensors, twist sensors, rotation sensors, circular birefringence, linear birefringence, FBG, polarization, optical fibers, Fiber Bragg Gratings
Objavljeno: 22.06.2017; Ogledov: 90; Prenosov: 10
.pdf Celotno besedilo (8,96 MB)

An EMI filter selection method based on spectrum of digital periodic signal
Marko Podberšič, Vojko Matko, Matjaž Šegula, 2006, izvirni znanstveni članek

Opis: This paper describes a new method for the selection of an appropriate signal lineElectromagnetic Interference (EMI) filter. To date, EMI filter selection has been based on the measurement of the radiation of the entire device. The new selection method based on the signal’s Fast Fourier Transform (FFT) measurement has proved to be efficient. The EMIfilter is optimized separately for each line. The method described in this paper involving aCentral Processor Unit (CPU) module demonstrates that the proposed FFT-based selection method is better than the radiation-based one. The radiation level in the frequency range 30MHz to 1 GHz is lower for approximate 2 – 6 dBμV/m.
Ključne besede: EMC, EMI filters, electrically long trace, typical frequency, sensor
Objavljeno: 22.06.2017; Ogledov: 62; Prenosov: 5
.pdf Celotno besedilo (189,00 KB)

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