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Block diagram of the sensor circuitry. It consists of a reference oscillator, a capacitively coupled tuned resonant circuit, a phase detector, a set of three analog switches, and a microcontroller.
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The efficiency of a gas turbine has an inverse relationship to the clearance between the rotor blades and the casing. Recent efforts in miniaturization of micro gas turbine engines have created a new challenge in blade tip clearance measurement. This paper describes the development of a capacitive tip clearance measurement system, based on a synchr...
Contexts in source publication
Context 1
... basic building blocks of the circuit are shown in Fig. 4. It consists of a reference oscillator, a tuned parallel resonant cir- cuit, a set of three analog switches, a probe capacitor, two ref- erence capacitors, a microcontroller, a digital-to-analog (D/A) converter, and a phase detector composed of two comparators, an analog mixer, and a low-pass filter. The purpose of the com- parators in ...
Context 2
... the dependency of the phase detector output on the phase dif- ference of the input signals. The probe tip capacitor and two reference capacitors are individually connected to the parallel resonant circuit through analog switches S1, S2, and S3. A ref- erence oscillator feeds the capacitively coupled resonant circuit. The phase detector shown in Fig. 4 transforms the phase differ- ence of the signals at the comparator inputs into voltage with zero volt output when the comparator input voltages are phase shifted by 90 . In resonance, the phase of a parallel resonant circuit is zero; hence, for a zero volt phase detector output, a 90 phase-shifted version of the reference signal is ...
Context 3
... detector output, a 90 phase-shifted version of the reference signal is needed. In previously reported work [38], the phase-shifted signal was obtained with a ded- icated 90 phase-shifting network. However, phase-shifting networks typically increase circuit complexity or the resulting phase-shift is frequency dependent. In the circuit shown in Fig. 4, the voltage across the resonant circuit is compared with the voltage across the coupling capacitor. In resonance, the par- allel resonant circuit is purely resistive and the voltage across the resonant circuit is therefore 90 phase-shifted relative to the voltage across the coupling capacitor ...
Context 4
... tip clearance sensor, as shown in Fig. 4, was imple- mented in two units. The first unit contained a microcontroller (Motorola 68HC912 evaluation board) and the second analog unit contained all the analog circuitry except the reference oscillator. During the entire testing, an external signal generator (Agilent Technologies 8648B synthesized RF signal generator) was used as a ...
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Citations
... The digital transformation of aviation requires new robust sensors for engine development, ground maintenance, and in-flight health management and prediction. Magnetic sensors are better suited for monitoring systems than optical [4] or capacitive sensors [5,6] because they do not require cleaning, and their signals can be processed using commonly available electronic systems. However, only sensors with high durability and reliability are acceptable. ...
Magnetic sensors are widely used in aeroengines and their health management systems, but they are rarely installed in the engine hot section due to the loss of magnetic properties by permanent magnets with increasing temperature. The paper presents and verifies models and design solutions aimed at improving the performance of an inductive sensor for measuring the motion of blades operated at elevated temperatures (200–1000 °C) in high pressure compressors and turbines. The interaction of blades with the sensor was studied. A prototype of the sensor was made, and its tests were carried out on the RK-4 rotor rig for the speed of 7000 rpm, in which the temperature of the sensor head was gradually increased to 1100 °C. The sensor signal level was compared to that of an identical sensor operating at room temperature. The heated sensor works continuously producing the output signal whose level does not change significantly. Moreover, a set of six probes passed an initial engine test in an SO-3 turbojet. It was confirmed that the proposed design of the inductive sensor is suitable for blade health monitoring (BHM) of the last stages of compressors and gas turbines operating below 1000 °C, even without a dedicated cooling system. In real-engine applications, sensor performance will depend on how the sensor is installed and the available heat dissipation capability. The presented technology extends the operating temperature of permanent magnets and is not specific for blade vibration but can be adapted to other magnetic measurements in the hot section of the aircraft engine.
... Blade Health Monitoring (BHM) systems have good commercial prospects, especially in power generation turbines which are increasingly operated in the off-design mode due to fluctuating market demand for energy. Magnetic sensors are better suited for monitoring systems than optical [2] or capacitive sensors [3,4] because they do not require cleaning, and their signals can be processed using commonly available electronic systems. However, only sensors with high durability and reliability are acceptable. ...
Magnetic sensors are widely used in health management systems for turbomachinery, but their applications in the hot zone are limited due to the loss of magnetic properties by permanent magnets with increasing temperature. The paper presents and verifies models and design solutions aimed at improving the performance of an inductive sensor for measuring the motion of rotating objects operating at elevated temperatures (200-1000°C), such as compressor and turbine blades. Physical, analog and mathematical models of the interaction of blades with the sensor were developed. A prototype of the sensor was made and its tests were carried out on the RK-4 rotor rig for the speed of 7000 rpm, in which the temperature of the sensor head was gradually increased to 1100°C. The sensor signal level was compared to that of an identical sensor operating at room temperature. The heated sensor works continuously producing the output signal whose level does not change significantly. What is more, a set of six probes passed an initial engine test in an SO-3 turbojet. It was confirmed that the proposed design of the inductive sensor is suitable for blade health monitoring of the last stages of compressors, steam turbines as well as previous generation gas turbines operating below 1000°C, even without a dedicated cooling system. In real-engine applications, sensor performance will depend on how the sensor is installed and the available heat dissipation capability
... 42 Then the research group developed a simple active tip-clearance control system based on a synchronous detection technology of a phase-modulated signal in the micro gas turbine, which made the applications of the sensor more extensive. 43 In their research, periodic autocalibration was used to reduce the effects of temperature drift on the sensor output. The main idea is to match the parasitic board capacitances arranged in parallel with the reference and the probe capacitors carefully. ...
Blade tip clearance is one of the important parameters affecting the performance, safety and stability of a gas turbine engine. However, it is difficult to measure the tip clearance in real time and accurately during the development and test process of an engine. In order to promote the development of tip clearance–measuring technology and the optimal design of the gas turbine engine, some typical measuring methods of tip clearance and a novel measuring method based on AC discharge are introduced. In this article, the significance for measuring tip clearance of an engine is illustrated first. Then, operating principles, characteristics and developments of those typical measurement approaches are introduced. After that, these methods are analyzed, and the particular characteristic of each measuring approach is summarized.
... When the excellent oxidation resistance is combined with the thermal stability of a high optical transparency [22,23], they can be applied for high-temperature passive protection of optical and optoelectronic devices. On the other hand, a combination of the high oxidation resistance and the thermal stability of the electrical conductivity makes them suitable for capacitive pressure, vibration or tip clearance sensors in severe oxidation environments [24][25][26][27]. ...
The high-temperature behavior of an electrically conductive, opaque and hard Hf7B23Si22C6N40 ceramic film with an amorphous structure was systematically investigated in air up to 1700 °C and inert gases up to 1600 °C. The film was prepared by reactive pulsed dc magnetron sputter deposition in an argon‑nitrogen gas mixture. The study is focused on the oxidation resistance of the film and the evolution of the structure, microstructure and elemental composition upon annealing in air and argon, and on the thermal stability of its hardness and electrical resistivity upon annealing in helium. The film exhibits an excellent oxidation resistance up to 1600 °C due to the formation of a compact protective oxide surface layer with a nanocomposite structure consisting of monoclinic and tetragonal/orthorhombic HfO2 nanocrystallites surrounded by a SiO2-based amorphous matrix. The film itself crystallizes into several phases such as HfB2, HfC0.5N0.5 and α-Si3N4 upon annealing but its elemental composition remains unaffected up to 1600 °C. In addition, the hardness and electrical resistivity exhibit also very high thermal stability.
... When the excellent oxidation resistance at elevated temperatures of thin-film materials is combined with a high optical transparency (e.g., as in the case of Si-B-C-N films 30,31 ), they can be used for high-temperature protective coatings of electronic and optical elements. Alternatively, a combination of the high oxidation resistance and electrical conductivity is desirable for harsh-environment sensors, such as capacitive pressure, vibration and tip clearance sensors (e.g., for advanced gas turbine engines [33][34][35][36]. ...
Recently, amorphous Hf-B-Si-C-N coatings found to demonstrate superior high-temperature oxidation resistance. The microstructure evolution of two coatings, Hf7B23Si22C6N40 and Hf6B21Si19C4N47, annealed to 1500 °C in air is investigated to understand their high oxidation resistance. The annealed coatings develop a two-layered structure comprising of the original as-deposited film followed by an oxidized layer. In both films, the oxidized layer possesses the same microstructure with HfO2 nanoparticles dispersed in an amorphous SiOx-based matrix. The bottom layer in the Hf6B21Si19C4N47 coating remains amorphous after annealing while Hf7B23Si22C6N40 recrystallized partially showing a nanocrystalline structure of HfB2 and HfN nanoparticles separated by h-Si3N4 and h-BN boundaries. The HfB2 and HfN nanostructures form a sandwich structure with a HfB2 strip being atomically coherent to HfN skins via (111)-Hf monolayers. In spite of the different bottom layer structure, the oxidized/bottom layer interface of both films was found to exhibit a similar microstructure with a fine distribution of HfO2 nanoparticles surrounded by SiO2 quartz boundaries. The high-temperature oxidation resistance of both films is attributed to the particular evolving microstructure consisting of HfO2 nanoparticles within a dense SiOx-based matrix and quartz SiO2 in front of the oxidized/bottom layer interface acting as a barrier for oxygen and thermal diffusion.
... In comparison to optical sensors, capacitive tip clearance sensors can be made smaller, more robust and cost effective. The change in capacitance between a blade tip and a turbine case is used as an indicator of tip clearance [15]. However, a capacitive sensor usually suffers from low accuracy and large measurement errors [16] because of the following reasons: (1) the case, shaft and surrounding blades, typically made of metallic materials, form parasitic capacitance, and (2) the changes in temperature, humidity and soot in the gas also affect the capacitance measurement. ...
Minimized tip clearance reduces the gas leakage over turbine blade tips and improves the thrust and efficiency of turbomachinery. An accurate tip clearance sensor, measuring the dynamic clearances between blade tips and the turbine case, is a critical component for tip clearance control. This paper presents a robust inductive tip clearance sensor capable of monitoring dynamic tip clearances of turbine machines in high-temperature environments and at high rotational speeds. The sensor can also self-sense the temperature at a blade tip in situ such that temperature effect on tip clearance measurement can be estimated and compensated. To evaluate the sensor's performance, the sensor was tested for measuring the tip clearances of turbine blades under various working temperatures ranging from 700 K to 1300 K and at turbine rotational speeds ranging from 3000 to 10 000 rpm. The blade tip clearance was varied from 50 to 2000 μm. The experiment results proved that the sensor can accurately measure the blade tip clearances with a temporal resolution of 10 μm. The capability of accurately measuring the tip clearances at high temperatures (∼1300 K) and high turbine rotation speeds (∼30 000 rpm), along with its compact size, makes it promising for online monitoring and active control of blade tip clearances of high-temperature turbomachinery.
... Kempe et al. [170] proposed an all-fiber, self-calibrating, economical probe capable of near-real-time, single-port, simultaneous blade-to-blade tip clearance measurements with sub-millimeter accuracy in the first stages of a gas turbine. To improve the gas turbine performance, Fabian et al. [171] investigated a control system used to maintain a constant blade tip clearance throughout the entire engine operation. ...
With the privatization and intense competition that characterize the volatile energy sector, the gas turbine industry currently faces new challenges of increasing operational flexibility, reducing operating costs, improving reliability and availability while mitigating the environmental impact. In this complex, changing sector, the gas turbine community could address a set of these challenges by further development of high fidelity, more accurate and computationally efficient engine health assessment, diagnostic and prognostic systems. Recent studies have shown that engine gas-path performance monitoring still remains the cornerstone for making informed decisions in operation and maintenance of gas turbines. This paper offers a systematic review of recently developed engine performance monitoring, diagnostic and prognostic techniques. The inception of performance monitoring and its evolution over time, techniques used to establish a high-quality dataset using engine model performance adaptation, and effects of computationally intelligent techniques on promoting the implementation of engine fault diagnosis are reviewed. Moreover, recent developments in prognostics techniques designed to enhance the maintenance decision-making scheme and main causes of gas turbine performance deterioration are discussed to facilitate the fault identification module. The article aims to organize, evaluate and identify patterns and trends in the literature as well as recognize research gaps and recommend new research areas in the field of gas turbine performance-based monitoring. The presented insightful concepts provide experts, students or novice researchers and decision-makers working in the area of gas turbine engines with the state of the art for performance-based condition monitoring.
... Pokud se změní vzdálenost mezi stěnou a lopatkou, změní se elektrické napětí mezi nimi. Aby bylo toto moţné, je potřeba, aby jak lopatka, tak stěna statoru byla dostatečně vodivá a zároveň vydrţela vysoké teploty, které jsou pro plynové turbíny typické a v budoucnosti se budou ještě zvyšovat [4]. ...
... Obr. 4 Značné sníţení tlaků, za kterých je výboj udrţitelný, a značné navýšení ionizace plazmatu v blízkosti terče, a tedy zvýšení depoziční rychlosti, znamenalo zavedení magnetronů. Elektrony z plazmatu nebo ty vytvořené sekundární emisí se zachytí ve zkříţeném elektrickém a magnetickém poli a driftují podél siločar. ...
... Všechny tyto efekty dohromady vysvětlují pozorovanou vysokou tvrdost vrstev HfBC a jsou v souladu s nadstechiometrickým TiB 2,4 [52] popsaném v kapitole 2.3.2. Vrstvy HfBC typu HfB 2 vykazují vysoké tlakové pnutí (4,9 GPa) hafniového terče se odráţí s tak vysokou energií, ţe se můţe snáze implantovat do rostoucí vrstvy (připomeňme, ţe obsah Ar ve vrstvách HfB(Si)C byl aţ 5 at.%.). Také můţe atom Ar, nalétávající na substráty s vysokou energií, zatlačit atomy B a C, jiţ přítomné na povrchu rostoucí vrstvy, a také je tak implantovat do vrstvy. ...
This Ph.D. thesis deals with synthesis of multicomponent nanocrystalline thinfilm materials, mainly from the HfB(Si)C(N) system, using pulsed magnetron sputtering. The thesis is divided into seven chapters. The first and second chapters are devoted to introduction and state of art of hard and electrically conductive hightemperature materials. In the third chapter, the four goals of the thesis are defined. In the fourth chapter, the methodology of preparation of the films, benefits of pulsed magnetron sputtering and methods for examination of plasma and prepared films are discussed. The fifth chapter is the most extensive and is devoted to the results achieved in this thesis. The fifth chapter is divided into four parts. Each of them deals with one goal of the Ph.D. thesis. In the first part of the fifth chapter, the HfB(Si)C films prepared by pulsed magnetron sputtering are discussed. It is shown that with increasing of the Si content in the target erosion area up to 7,5 %, there is a rapid reduction in compressive stress (from 5 to 1 GPa) at a remaining high hardness (around 37 GPa). Moreover, increasing of the Si content results in increasing of oxidation resistance of HfSiBC films (no detectable oxide layer after oxidation up to 800 °C) at a remaining high electrical conductivity of this material (electrical resistivity on the order of m). In the second part of the fifth chapter, the discharge plasma was analyzed by mass spectroscopy during preparation of MBCN (M = Ti, Zr, Hf) films and the dominant effect of U0 (the voltage during the positive voltage overshoot after the negative voltage pulse) on the maximum detected energy of Ar+ ions was proven. U0 can be affected by pressure and power during the deposition. Using the mass spectroscopy and calculations it is also shown that the energy of Ar atoms backscattered from the B4CHf target is several times higher than the energy of Ar atoms backscattered from the B4CZr and B4CTi targets. In the third part of the fifth chapter, mechanical and optical properties and especially oxidation resistance of the HfBSiCN films prepared by pulsed magnetron sputtering are reported. An oxidation barrier composed of HfO2 nanoparticles in the SiO2based glassy matrix is formed during oxidation which prevents a further oxidation. The oxidation resistance of these materials up to 1500 °C is reported. In the fourth part of the fifth chapter, similar films as in the third part of fifth chapter are reported. They were prepared after the renovation of the deposition system, which led to a lower base pressure. The oxidation resistance of the HfBSiCN films is reported with another improvement which was achieved by decreasing of the pulse length from original 85 s to 50 s. The HfBSiCN film prepared at 15 % N2 in the reactive gas mixture with the pulsed length of 50 s exhibited a higher oxidation resistance at elevated temperatures. The thickness of the oxide layer after the oxidation up to 1500 °C was by 200 nm lower than for the similar HfBSiCN films prepared before the renovation of the deposition system with the pulse length of 85 s. In the sixth chapter, the conclusions of the thesis are presented. Its last chapter is devoted to references.
... A simple temperature drift compensation method utilizing a noninductive compensating coil was developed in [14]. Fabian et al. pointed out in [15] that the temperature drift of ECSs can be reduced by either minimizing the board capacitance, or by matching the parasitic board capacitances at the input of all three analog switches. Nabavi and Nihtianov [16] proposed a new front-end circuit for eddy-current displacement sensors utilizing a standard 0.35-µm CMOS technology, which demonstrates excellent thermal stability, high resolution, and low-power consumption. ...
The output stability of the displacement sensors is an important issue for safe operations in magnetic bearing supported high-speed rotor system. This paper proposes an effective postprocessing solution to the problems of temperature drift and synchronous measuring error for the axial displacement sensor in a 10-kW magnetically suspended motor. The proposed configuration of the axial displacement sensor consists of three probes: one pair is used to eliminate the synchronous measuring error, and the third probe is employed for the consideration of temperature drift. First, the generating mechanism of the synchronous measuring error caused by the improper assemble is presented, and an operational amplifier is proposed to obtain an accurate position of the axial center by adjusting the weights of sensing signals from one pair of probes. Then the scheme of temperature compensation using an auxiliary probe is presented. In order to obtain accurately the characteristics of temperature drift at the operating point, the detailed procedure is given to determine the temperature-drift ratio. Finally, the terms related to temperature drift and synchronous error in the final output of the displacement sensor are both eliminated. Experimental results on a magnetically suspended motor test rig show the effectiveness of the proposed solution.
... Moreover DC systems have a relatively poor frequency response, making their calibrations highly rotation speed dependent [11]. FM capacitance probe can be also used for the measurement of blade vibrationby tip-timing [11][12][13]. ...
This paper deals with the development of a system aimed at the characterization of turbomachinery tip clearance measurement instruments based on frequency modulated (FM) capacitance probes. The proposed system is able to accurately measure the dynamic response of the systems under testavoiding any mechanical moving part, ensuring in this way a faster, more accurate and versatile characterization procedure. The work introduces the characterization by means of a simple model of tip clearance measurement systems, which allows to obtain a straightforward relationship between the bandwidth and the clearance measurement accuracy. The experimental setup of the proposed system is described, and some data related to two different clearance measurement systems are shown.
