Techniques for blade tip clearance measurements with capacitive probes alexander steiner hytron gmbh, georg schr. The proxisense system utilises an eddy current sensor with proven reliability. The combined sensor uses a pressure sensor in the centre and is enclosed by an eddy current sensor forming a compact single package. Laser based optic probe can measure the blade tip clearance. Evaluation and improvement of eddy current position sensors in magnetically suspended flywheel systems timothy p. Tipclearance measurements on an engine high pressure turbine. A major advantage the eddy current sensor over the other.
Evaluation and improvement of eddy current position sensors. This section gives a short description on how to build a probe part number. Blade vibration and clearance are important diagnostic features for condition monitoring, including the detection of blade cracks. The stator ring and the control ring are coupled together and mounted within the component by a plurality of radial. This catalogue features the standard range of ge eddy current probes and accessories. Analysis of eddycurrent losses over conductive substrates with applications to monolithic inductors and transformers ali m. A new high temperature eddy current sensor has been developed for application in turbo machinery tiptiming and tip clearance measurements to assess blade. Thus, quantitative inversion of eddy current signals to obtain flaw sizes requires methods for calibrating eddy current measurement systems. The system provides an output voltage that is directly proportional to the distance between the probe tip and the observed conductive surface. Eddy current probes all specifications are subject to change without notice. Modelling and experimental validation of active and passive eddy current sensors for blade tip timing.
It is usually used to measure blade tip clearance in kaplan turbines as well as runner band clearance. This requires detailed modeling of eddy current sensors in the blade tip timing application. The firstofitskind experimental data from transient thermal measurements. During steady state operations, aircraft engine blade tip clearance and interblade spacing remain constant.
The cmss 785 system is an eddy current type noncontact displacementvibration system, used for measuring shaft vibration, axial position, rotating speed and phase. A passive clearance control system for a gas turbine engine component. This paper presents a robust inductive tip clearance sensor capable of monitoring dynamic tip clearances of turbine machines in hightemperature environments and at high rotational speeds. The sensors were flush mounted with the inner wall of the casing, the cold blade tip clearance was estimated to be approximately3. Pdf eddy current sensor system for blade tip clearance. Investigation on the turbine blade tip clearance monitoring. Formation of fatigue damage in engine disk slots and. Sensing systems based on optics, capacitance, eddy current and microwave are present for tip clearance measurement. Rotating bladed disk, blade tip timing, eddy current sensors, blade tip clearance, coupled mechanical and electromagnetic problem. Simulating eddy current sensor outputs for blade tip timing. The dynamic experiment proved the measuring range, resolution, response speed of designed sensor can meet the requirement of turbine blade tip clearance measurement. The illustrations shown are for reference only and may not be to scale. The drawings below represents schematically how does eddy current works.
Verification and design of high precision eddy current sensor. The measurements shown in the tables are metric with the equivalent imperial size in brackets i. Their use in this application is well established and measurement accuracy is high. Different types of sensors are used to measure the tip clearance values in gas turbine engine. Two types of eddy current sensors were deployed to detect foded blades and dynamic fod events, mm and 6mm. A plurality of vane sectors define a stator ring including a blade shroud. Development of a combined eddy current and pressure sensor. Meyer, fellow, ieee abstract in this paper, a closedform integral representation for the eddycurrent losses over a conductive substrate is presented. Evaluation and improvement of eddy current position. Eddy current probe tip to tip clearances although probe tip to tip clearances are not normally an issue on most machines, it should be noted that eddy current probes radiate an rf field larger than the probe tip itself. During steady state operations, aircraft engine blade tip clearance and inter blade spacing remain constant. The sensor is designed to withstand temperatures of order 1500 to 1600k. Specifications are liable to change without notice.
Eddy current sensor system for blade tip clearance measurement based on a speed adjustment model. One way to reduce an aircraft engines emissions and improve engine performance is through active clearance control acc. Blade tip timing is a contactless method used to monitor the vibration of blades in rotating machinery. The signal feeds directly into a digital signal processor that is capable of processing 12 signals simultaneously including signals from other types of sensors. A highfrequency hf electromagnetic field is emitted by a coil of the eddy current sensor. Us6935836b2 compressor casing with passive tip clearance. And the future work will focus on the high temperature issues.
Simulating eddy current sensor outputs for blade tip timing nidhal. Blade tip sensors are commonly used for monitoring bladed disks in rocket and gas engines, as well as in steam turbines. Experimental investigation of high temperatureresistant. The combined sensor uses a pressure sensor in the centre and is enclosed by an eddy current sensor forming a. In the case of air core reactors carrying alternating current, the stray magnetic field will induce eddy currents and associated eddy current losses in any electrically conductive parts which reside in the stray field, whether they be made of either ferromagnetic or nonmagnetic material. Direct or indirect measurement of blade parameters time, clearance, vibration, pitch angle, etc is generally performed through optical, capacitive, and eddy current sensors 3.
Type coil tip angle length drop frequency shaft size connector part id item n. A new high temperature eddy current sensor has been developed for application in turbomachinery tip timing and tip clearance measurements to assess blade vibrations. Jul 08, 2010 furthermore, since the output of an eddy current sensor depends in part upon the distance between the passing target object and the sensing coil, this type of sensor has the ability to provide information on blade tip clearances as well as tip timing. The first involves a capacitancebased blade tip clearance measurement system 2 developed under phase i and ii sbir. This paper is intended to provide insight into these phenomena so that improved high frequency. Get more information about eddy current brakes pdf download by visiting this link. Modelling and experimental validation of active and passive. The proposed development program will focus on the use of throughthecase eddy current sensors to measure blade tip clearance in real time. Buckley pdf, 429 kb eddy current testing at level 2, international atomic energy agency, vienna, 2011 pdf 5. Some industries are currently using capacitive sensing system for blade tip clearance measurement. The mathematical methods employed in solving the relevant problems are. Aug 17, 2017 a new combined sensor that can measure tip timing, tip clearance and dynamic pressure was developed at the university of oxford for use in gas turbine engine health monitoring. The eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. The efficiency and reliability of turbomachinery will be improved by blade tip clearance btc and blade tip timing btt monitoring.
Eddy current transducer installation part 1radial vibration. Simulating eddy current sensor outputs for blade tip. High temperature eddy current sensor system for turbine. The mm sensors have a range up to 7mm whereas the 6mm sensors have a range of about 3mm. Is it costeffective to replace old eddycurrent drives. In this study, the influence of tip clearance size on the steady flowfield and aerodynamic damping is. When the changing flux links with the core itself, it induces emf in the core which in turns sets up the circulating current called eddy current. While eddy current sensors of various forms are knownincluding passive types where. The spatial penetration of a blade tip into the hf electromagnetic field induces eddy currents in the blade tip. Pdf blade tip timing is a contactless method used to monitor the vibration of blades in rotating machinery. A numerical method for blade tip timing using an eddy current sensor is described in section the simulation of blade tip timing using an ecs, where mesh details and. Pdf simulating eddy current sensor outputs for blade tip timing. This model is demonstrated by simulating the effect of tip clearance, blade geometry, and blade velocity on the output of the eddy current. Several eddy current sensor installations have been in continuous operation for over 2 years in gas turbine engines and steam turbines with no degradation in signal quality.
Blade tip timing and blade tip clearance measurement. Completely from experimental perspective, the present study aimed to address the walltogas temperature ratio effect on turbine blade tip heat transfer. Eddy current sensor system for blade tip clearance measurement. To overcome this downside, eddy current sensors are a good. Pdf blade tip clearance btc measurement and active clearance control acc are becoming crucial technologies in aeroengine health monitoring so as. Although probe tip to tip clearances are not normally an issue on most machines, it should be noted that proximity probe probes radiate an rf field larger than the probe tip itself.
Eddy current technique is an important electromagnetic nondestructive evaluation technique that is widely used in power, aerospace, petrochemical and other industries for detection of surface. Modelling and experimental validation of active and. The sensors are rugged and are often used in contaminated environments. Eddy current technique is an important electromagnetic non. The objective of this project is to develop large eddy simulation capability for flows through an axial flow rotor with tip clearance, and to gain a physical understanding of the unsteady flow characteristics in the endwall region downstream of the rotor. To monitor the vibration of blades in rotating machinery, the contactless method called blade tip timing btt is widely used.
Blade tip clearance btc measurement and active clearance control acc are becoming crucial technologies in aeroengine health monitoring so as to. Assessment of eddy current testing for the detection of. Underwater eddy current proximity sensor users manual. Todays highperformance eddy current proximity sensors deliver continuous condition monitoring. Blade tip clearance btc measurement and active clearance control acc are becoming crucial technologies in aeroengine health monitoring so as to improve the efficiency and reliability as well as to ensure timely maintenance. Eddy current probe catalog introduction 6 every section in this probe catalog begins with a short description of the different eddy current products available. Calibration of eddy current measurement systems is an important factor for attaining the accuracy and precision of measurement that quantitative nondestructive evaluation requires. Aircraft engine blade tip monitoring using pulsed eddy current. Each eddy current probe available from ndts has a unique code. Influence of the tip clearance on a compressor blade. The investigation encompasses development and validation of an integrated sensor design to provide tip clearance measurements.
Electronic pulsewidthmodulated pwm variable frequency drives vfd may be costeffective replacements for aging or highmaintenance eddy current drives that are used with variable torque loads, such as centrifugal fans or pumps. The system can measure both static position and dynamic vibration data. Among other things, it explains i why eddy current losses increase so dramatically with more wind. Author links open overlay panel nidhal jamia a michael i.
The past investigations using eddy current testing in blade tip. Pdf blade tip clearance btc measurement and active clearance control acc are becoming crucial technologies in aeroengine health. A new high temperature eddy current sensor has been developed inhouse at the. Eddy current sensors were the first noncontact sensors developed and dealt with in the institute in early 1990s. Noncontacting blade tip sensors the type of sensor selected depends upon a number of factors including, environment, standoff distance, resolution, duration of test and whether blade tip clearance monitoring is required. The coil red causes a magnetic field, which initiate eddy current.
Us6927567b1 passive eddy current blade detection sensor. If a defect appears in the effective area, the eddy current have to take a different way, this changes the impedance of. As an example, model cmss65 and 68 probe should never be installed with less than one 1 inch of probe tip to tip clearance. The effect of sensor characteristics on blade tip timing. The measurement of the tip clearance and the time of arrival of every single blade in rotating turbo machinery is the starting point to characterize the performance of a rotating turbine. We study the effects of tip clearance and blade velocity on the measurement. The doubleleakage tip clearance flow, its interaction with the tip clearance core vortex of the adjacent blade, and the resulting large mixing loss are the main flow mechanism of the large rotor tip gap in the compressor. Abstract blade tip timing is a contactless method used to monitor the vibration of blades in. A transmitreceive pulsed eddy current probe that could detect changes in the blades coordinates was employed for this purpose.
Existing simulations for eddy current sensors have not considered the particular case of a blade rotating past the sensor. Proximity sensors, probes and transducer systems bently nevada. Meyer, fellow, ieee abstract in this paper, a closedform integral representation for the eddycurrent. In order to provide strong validation for the current study, it was decided to. Eddy current transducer installation part 2thrust position. A new combined sensor that can measure tip timing, tip clearance and dynamic pressure was developed at the university of oxford for use in gas turbine engine health monitoring. And these current in return produces a loss called eddy current loss or i 2 r loss, where i is the value of the current and r is the resistance of the eddy current path. The system provides a blade shroud that is isolated from the component case and can move radially to maintain blade clearance. If you cannot find a probe or accessory to meet your inspection requirements, please contact your local. Pdf blade tip clearance and time of arrival immediate. Hood technology has built a large number of optical and eddy current sensors for testing on many different platforms. The effect of sensor characteristics on blade tip timing measurements n. Proximity sensors, probes and transducer systems bently. Calibration methods for eddy current measurement systems.
The results showed the sensor was able to perform at these extreme environments without losing accuracy. Maintaining turbine clearance control of aircraft gas turbines. In assessing the et inspection technique, pnnl used a range of specimens from four different sources. Tai services will supply all materials, labor and test equipment needed for the inspection.
Analysis of eddycurrent losses over conductive substrates. Various sensing strategies have been proposed over the years to measure blade tip clearance. Based on their approach, the tip clearance measurements and the blade tip timing were simultaneously measured, leading to lower cost and time requirements. The electrically conductive blade allows eddy currents to flow briefly as it passes. This study details development of a high temperature eddy current sensor system for hot section applications. General surface probes, aerospace probes, dedicated inspection probes and accessories.
Present industrial standard sensors used in tip timing systems such as optical, capacitance, hall effect etc. Non destructive testing eddy current testing, wirbelstrom. An accurate tip clearance sensor, measuring the dynamic clearances between blade tips and the turbine case, is a critical component for tip clearance control. Hood tech blade vibration monitoring capabilities overview.
An introduction to eddy current testing from the ndendt resource center. An eddy current sensor for use as a dynamic proximity sensor, particularly for monitoring of blade tip timing and clearance in turbomachinery, has a common coil for use in both generating a magnetic field in a proximate region and detecting the effect of eddy currents generated by said field in electrically conductive objects passing through that region. Jansen ohio aerospace institute, brook park, ohio prepared for the. A passive blade detection sensor exploits the electrically conductive trait of typical turbo machinery components such as fan, compressor and turbine blades. Eddy current is the swirling current produced in a conductor, which is subjected to a change in magnetic field. To properly calibrate an eddy current probe, several possibilities exist. This sensor is used for timeofarrival and for uncalibrated tip clearance measurements. The quantity of interest in most forms of eddy current inspection is z, the change in probe impedance induced by a flaw. This is achieved by the use of a coil connected to an alternating current generator driving an alternating magnetic field primary field.
Different types of probes have been proposed and are currently used to monitor these parameters. The work provides experience in eddy current sensor design in different application, not only in turbine. The development of a hot section eddy current sensor for. As an example, model cmss65 and 68 should never be installed with less than one 1 inch of probe tip to tip clearance. The sensing strategies used for the purpose of measuring are based on microwaves sensing system, capacitance probe, laser, optics and eddy currents. Eddy current sensor system for blade tip clearance. Furthermore, the relative severity of a discontinuity may be indicated, and a rejection level may be set with respect to the magnitude of. Eddy current technique is an important electromagnetic nondestructive evaluation technique.
They can provide highly accurate blade tip timing data in both analogue and digital forms and in realtime. Modelling and experimental validation of active and passive eddy. Online monitoring of dynamic tip clearance of turbine blades. Eddy current sensor ecs offers an attractive option for btc measurement due to its robustness, whereas current approaches have not considered two issues sufficiently. Eddy current sensors in tip timing eddy current sensors are most commonly used for non contact proximityand displacement measurements. Rao nondestructive evaluation division metallurgy and materials group indira gandhi center for atomic research kalpakkam 603 102, tn, india email. The question arises of what level of detailing is necessary for accurate aerodamping predictions. Aircraft engine blade tip monitoring using pulsed eddy. Tipclearance measurements on an engine high pressure turbine using an eddy current sensor. Portable and lightweight, our eddy current array flaw detection solutions including an extensive series of compatible test probes are designed for high frequency surface to low frequency subsurface inspections for weld, aerospace including rotary and general purpose inspections. Spc371r1afe spring loaded probe spc629 spc4161 spc624diffinc spc623diffinc spc621 flangetube well spc620mtl. Several types of sensors such as eddy current, capacitance and optical probes are used to realize this objective. Eddy current losses in transformer windings and circuit wiring. Although eddy probe tip to tip clearances are not normally an issue on most machines, it should be noted that eddy probes radiate an rf field larger than the probe tip itself.
Many different sensing principles have been utilized for tip clearance and tip timing measurements. Verification and design of high precision eddy current. This is achieved by managing the clearance between the gas turbine casing and the tips of the rotating blades, referred to as turbine tip clearance. A permanent magnet is placed strategically adjacent to a wire coil to generate a single pulseantipulse signal when a blade passes in front of the sensor. To effectively monitor the vibration of blades in a rotating machine, a non contacting method called blade tip timing btt has been used. Astm e3052 standard practice for examination of carbon steel welds using eddy current array. As an example, model cmss65 and 68 probes should never be installed with less than one 1 inch of probe tip to tip clearance.
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