Patent Publication Number: US-7582359-B2

Title: Apparatus and method of monitoring operating parameters of a gas turbine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of pending U.S. patent application Ser. No. 11/122,566 filed May 5, 2005, which claims the benefit of Provisional Patent Application No. 60/581,662 filed on Jun. 21, 2004, which is also a continuation-in-part of U.S. patent application Ser. No. 11/018,816 filed Dec. 20, 2004, now U.S. Pat. No. 7,270,890 which is a continuation-in-part of U.S. patent application Ser. No. 10/252,236 filed Sep. 23, 2002, now U.S. Pat. No. 6,838,157 all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to monitoring parameters of operating environments and particularly to an apparatus and method of determining wear behavior of an abradable coating system deposited on components within an operating environment such as a gas turbine engine. 
     BACKGROUND OF THE INVENTION 
     Gas combustion turbines are used for a variety of applications such as driving an electric generator in a power generating plant or propelling a ship or an aircraft. Firing temperatures in modern gas turbine engines continue to increase in response to the demand for higher efficiency engines. Superalloy materials have been developed to withstand the corrosive high temperature environment that exists within a gas turbine engine. However, even superalloy materials are not able to withstand extended exposure to the hot combustion gas of a current generation gas turbine engine without some form of cooling and/or thermal insulation. 
     Thermal barrier coatings are widely used for protecting various hot gas path components of a gas turbine engine. The reliability of such coatings is critical to the overall reliability of the machine. The design limits of such coatings are primarily determined by laboratory data. However, validation of thermal barrier coating behavior when subjected to the stresses and temperatures of the actual gas turbine environment is essential for a better understanding of the coating limitations. Such real world operating environment data is very difficult to obtain, particularly for components that move during the operation of the engine, such as the rotating blades of the turbine. 
     Despite the extreme sophistication of modem turbine engines, such as gas turbines for generating electrical power or aircraft engines for commercial and military use, designers and operators have very little information regarding the internal status of the turbine engine components during operation. This is due to the harsh operating conditions, which have prevented the use of traditional sensors for collecting reliable information of critical engine components. 
     Many current turbines are equipped with sensors capable of limited functions such as exhaust gas-path temperature measurements, flame detection and basic turbine operating conditions. Based on this information, turbine operators such as utility companies operate engines in a passive mode, in which maintenance is scheduled based on prior histories of similar engines. Engine rebuilds and routine maintenance are performed in the absence of a prior knowledge of the remaining or already utilized life of individual components. The lack of specific component information makes early failure detection very difficult, often with the consequence of catastrophic engine failure due to abrupt part failure. This results in inefficient utilization, unnecessary downtime and an enormous increase in operating cost. 
     Currently, the gas turbine industry approach is to depend on the measurement of gas path temperature, which is related back to specific component problems based on experience and history regarding a class of engines. This approach is highly subjective and only allows for determining already severe situations with an engine. It does not provide indications of impending damage or insight into the progression of events leading up to and causing engine damage due to component degradation or failure. 
     The instrumentation of a component such as a blade or vane within a steam turbine typically includes placing wire leads on the balance wheel, which continue on to the blade airfoil. The wire leads are typically held together by an epoxy. These wires are routed from within the component to the turbine casing. The pressure boundary of a component may be breached to introduce a sensor such as a thermocouple and a braze is back filled to hold the thermocouple in place. Each thermocouple sensor has wire leads coming out of the component that are connected back to a diagnostic unit. Instrumenting a plurality of components of a turbine in this manner results in an extensive network of wires just for monitoring the single operating condition of temperature. Instrumenting components using this technique is expensive, which is a barrier to instrumenting a large number of components within a single turbine. Further, the wire leads and data transfer is frequently poor, which can result in costly repairs and flawed data analysis. 
     Using thermocouples for temperature measurements in the gas path of a turbine may be disadvantageous because it only provides feedback to an operator that a temperature change has occurred in the gas path. It does not provide any indication as to why the temperature change has occurred. For diagnosing problems with blades or vanes based on a measured temperature change, there has to be an historical correlation between the measured temperature differential and the specific problem, such as a hole in a vane. This correlation is difficult and time consuming to derive to within a reasonable degree of certainty and needs to be done on an engine-by-engine basis taking into account turbine operation conditions. When a temperature differential is measured, it is difficult, if not impossible, to predict what the problem is or where it is located. Consequently, the turbine must typically be shut down and inspected to determine the scope of repair, replacement or other maintenance to be performed. 
     In any application, combustion turbines are routinely subject to various maintenance procedures as part of their normal operation. Diagnostic monitoring systems for gas turbines commonly include performance monitoring equipment that collects relevant trend and fault data used for diagnostic trending. In diagnostic trend analysis, certain process data (such as exhaust gas temperature, fuel flow, rotor speed and the like) that are indicative of overall gas turbine performance and/or condition are compared to a parametric baseline for the gas turbine. Any divergence of the raw trend data from the parametric baseline may be indicative of a present or future condition that requires maintenance. Such diagnostic monitoring systems can only predict or estimate specific component conditions and do not collect data from or provide any analysis with respect to the actual condition of a specific component itself. 
     In this respect, conventional methods of predicting component failure for gas turbines and of scheduling maintenance have not been entirely accurate or optimized. The traditional “duty cycle” used for predictive maintenance does not reflect real operational conditions, especially off-design operations. The actual life of specific components of a gas turbine depends strongly on the actual usage of that gas turbine and the specific components within the turbine. 
     For example, elevated temperatures and stresses within the turbine, and aggressive environmental conditions may cause excessive wear on components in the turbine beyond that predicted with the standard design duty cycle. Off-design operating conditions, which are often experienced by industrial gas turbines, are not reflected by the standard duty cycles. The actual life of components in the gas turbine may be substantially less than that predicted by the design duty cycle. Alternatively, if more favorable conditions are experienced by an actual gas turbine than are reflected in the design duty cycle, the actual component life may last substantially longer than that predicted by maintenance schedules based on the design duty cycle. In either event, the standard design duty cycle model for predicting preventive maintenance does not reliably indicate the actual wear and tear experienced by gas turbine components. 
     Known techniques for predicting maintenance and component replacement rely on skilled technicians to acquire or interpret data regarding the operation of a combustion turbine. Such techniques are subject to varying interpretations of that data by technicians. Technicians may manually evaluate the operational logs and/or data collected from gas turbines. Technicians, for example, may evaluate start and stop times and power settings to determine how many duty cycles had been experienced by the gas turbine, their frequency, period and other factors. In addition, if the data log of a gas turbine indicated that extraordinary conditions existed, such as excessive temperatures or stresses, the technicians may apply “maintenance factors” to quantify the severity of these off-design operational conditions. 
     None of these techniques provide accurate information with respect to the actual condition of a specific component or component coating, which may lead to unnecessary repair, replacement or maintenance being performed causing a significant increase in operating costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of an exemplary combustion turbine with which embodiments of the invention may be used and an exemplary monitoring and control system for collecting and analyzing component data from the combustion. 
         FIG. 2  a perspective view of an exemplary combustion turbine vane equipped with an exemplary embodiment of the present invention. 
         FIG. 3  is a schematic view of a vane of  FIG. 2 . 
         FIG. 4  is a schematic cross section of the compressor of  FIG. 1 . 
         FIG. 5  is a perspective partial view of an exemplary embodiment of a smart component combustion in accordance with aspects of the invention. 
         FIG. 6A  is a schematic view of an exemplary embodiment of the component of  FIG. 5 . 
         FIG. 6B  is a schematic view of an exemplary embodiment of the component of  FIG. 5 . 
         FIG. 6C  is a schematic view of an exemplary embodiment of the component of  FIG. 5 . 
         FIG. 7  is an exemplary embodiment of a heat flux sensor. 
         FIGS. 8 and 9  illustrate an exemplary embodiment of a strain gauge and a crack propagating to different lengths. 
         FIG. 10  is a partial perspective view of a component having a sensor embedded within a layer of thermal barrier coating material disposed over a substrate material. 
         FIG. 11  is a partial cross-sectional view of a component having a plurality of sensors embedded at varying depths below a surface of the component. 
         FIG. 12  is a process diagram illustrating steps in a method of manufacturing the component of  FIG. 11 . 
         FIG. 13  is a partial cross-sectional view of a component having a plurality of sensors embedded at varying depths below a surface of the component. 
         FIG. 14  is schematic plan view of an exemplary microelectromechanical system (MEMS) device. 
         FIG. 15  is a perspective view of exemplary MEMS device embedded in an abradable coating system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention may use microelectromechanical systems (MEMS) devices as sensors embedded within various types of coatings recognized by those skilled in the art. For example, barrier coating may be used herein generally to refer to a range of coatings commonly used in combustion turbine engines such as abradable coating systems, thermal barrier coatings, CMC coatings, wear coatings, protective overlay coatings, insulating coatings and restoration coatings as well as others. Reference to specific types of coatings herein is by way of example only. 
     MEMS devices may be embedded in barrier coatings and/or affixed on or within a surface of components to enable monitoring and diagnostics of a system such as an exemplary combustion turbine  10  of  FIG. 1 . Using MEMS devices is advantageous because they may be placed directly at locations of interest due to their small size and robust electrical connections. Locating MEMS devices directly at locations of interest provides an increased accuracy in measurements relative to remote sensors that are located away from the locations of interest, in which case measurements must be extrapolated to predict events at the location of interest. MEMS devices may be coupled with antenna located on their respective silicon chips for wireless transmission of data indicative of the desired properties being measured or monitored. 
       FIG. 1  illustrates an exemplary combustion turbine  10  such as a gas turbine used for generating electricity as will be recognized by those skilled in the art. Embodiments of the invention may be used with combustion turbine  10  or in numerous other operating environments and for various purposes as will be recognized by those skilled in the art. For example, embodiments may be used in aircraft engines, monitoring temperature and heat flux in boilers, heat exchangers and exhaust stacks; determining insulation performance and degradation; determining pipe fouling; and evaluating vibrating component health. Embodiments may be used in the automotive industry for monitoring combustion chamber conditions, rotating components such as crankshaft, cams, transmissions and differentials, and determining suspension and frame integrity for heavy-duty vehicles. Embodiments may also be used in measuring strain and heat flux in tanks, portable and other equipment operating in dessert, wet, and/or high temperature configurations. 
     Returning to  FIG. 1 , combustion turbine  10  includes a compressor  12 , at least one combustor  14  (broken away) and a turbine  16 . Compressor  12 , combustor  14  and turbine  16  are sometimes referred to collectively as a gas turbine engine. Turbine  16  includes a plurality of rotating blades  18 , secured to a rotatable central shaft  20 . A plurality of stationary vanes  22  are positioned between blades  18 , with vanes  22  being dimensioned and configured to guide air over blades  18 . Blades  18  and vanes  22  will typically be made from nickel-cobalt, and may be coated with a thermal barrier coating  26 , such as yttria-stabilized zirconia. Similarly, compressor  12  includes a plurality of rotating blades  19  positioned between respective vanes  23 . 
     In use, air is drawn in through compressor  12 , where it is compressed and driven towards combustor  14 . Combustor  14  mixes the air with fuel and ignites it thereby forming a working gas. This working gas will typically be above 1300° C. This gas expands through turbine  16 , being guided across blades  18  by vanes  22 . As the gas passes through turbine  16 , it rotates blades  18  and shaft  20 , thereby transmitting usable mechanical work through shaft  20 . Combustion turbine  10  may also include a cooling system (not shown), dimensioned and configured to supply a coolant, for example steam or compressed air, to blades  18  and vanes  22 . 
     The environment wherein blades  18  and vanes  22  operate is subject to high operating temperatures and is particularly harsh, which may result in serious deterioration of blades  18  and vanes  22 . This is especially likely if the thermal barrier coating  26  should spall or otherwise deteriorate. Embodiments of the invention are advantageous because they allow components to be configured for transmitting data indicative of a component&#39;s condition during operation of combustion turbine  10 . Blades  18 ,  19 , vanes  22 ,  23 , and coatings  26 , for example, may be configured for transmitting component specific data that may be directly monitored to determine the respective condition of each component during operation and to develop predictive maintenance schedules. 
       FIG. 1  also illustrates a schematic of an exemplary monitoring and control system  30  that may be used in accordance with various aspects of the present invention. System  30  may include an antenna  32 , a receiver  33 , a processor or CPU  34 , a database  36  and a display  38 . Processor  34 , database  36  and display  38  may be conventional components and antenna  32  and receiver  33  may have performance specifications that are a function of various embodiments of the invention. For example, antenna  32  and receiver  33  may be selected for receiving wireless telemetry data transmitted from a plurality of transmitters deployed in various locations throughout combustion turbine  10  as more fully described below. 
     Embodiments of the present invention allow for a plurality of MEMS sensors to be embedded within the respective coatings of a plurality of components within combustion turbine  10 . Alternate embodiments allow for the sensors to be surface mounted or deposited to components, especially those contained in areas where components do not require a barrier coating such as the compressor. Exemplary embodiments of sensors may be used to provide data to system  30  with respect to physical characteristics of a component and/or properties of a component&#39;s coating as well as other component or coating specific information. 
     For example, exemplary sensors may be used to detect wear between two components, measure heat flux across a component&#39;s coating, detect spalling of a coating, measure strain across an area of a component or determine crack formation within a component or coating. MEMS sensors may be configured as proximity probes, accelerometers, load cells, pressure transducers, strain gauges, temperature probes, heat flux sensors, vibration sensors and gas sensors. Those skilled in the art will recognize other properties and/or characteristics of a component, component coatings and operating parameters of combustion turbine  10  that may be monitored, measured and/or detected in accordance with aspects of the invention. 
     It will be appreciated that aspects of the invention allow for various MEMS sensor configurations to be embedded within a barrier coating such as a barrier coating  26  of blades  18  or vanes  22  of turbine  16 . U.S. Pat. No. 6,838,157, which is specifically incorporated herein by reference, describes various embodiments of methods for instrumenting gas turbine components, such as blades  18  and vanes  22  that may be utilized for depositing MEMS sensors in accordance with aspects of the present invention. This patent discloses various methods of forming trenches in a barrier coating, forming a sensor in the coating and depositing a backfill material in the trench over the coating. Embodiments of those methods and components may be used to form smart components incorporating MEMS sensors as disclosed herein. 
     U.S. Pat. No. 6,576,861, which is specifically incorporated herein by reference, discloses a method and apparatus that may be used to deposit embodiments of sensors and sensor connectors with transmitters in accordance with aspects of the present invention. In this respect, methods and apparatus disclosed therein may be used for the patterning of fine sensor and/or connector features of between about 100 microns and 500 microns without the need of using masks. Multilayer electrical circuits and sensors may be formed by depositing features using conductive materials, resistive materials, dielectric materials, insulative materials and other application specific materials. It will be appreciated that other methods may be used to deposit multilayer electrical circuits and sensors in accordance with aspects of the invention. For example, thermal spraying, vapor deposition, laser sintering and curing deposits of material sprayed at lower temperatures may be used as well as other suitable techniques recognized by those skilled in the art. 
     Embodiments of the invention allow for a plurality of sensors  50 , which may be MEMS devices to be deployed in numerous places within combustion turbine  10  for monitoring component-specific or coating-specific conditions as well as collecting other data with respect to the operation or performance of combustion turbine  10 . For example,  FIG. 1  illustrates that one or more sensors  50  may be embedded within respective barrier coatings  26  of one or more blades  18  of turbine  16 . It will be appreciated that sensors  50  may be embedded within barrier coatings of other components with turbine  16  for which component-specific and/or coating-specific data is to be acquired. 
       FIG. 2  illustrates a pair of vanes  23  removed from compressor  12  with one vane having a sensor  50  mounted or connected with vane  23  for detecting a condition of vane  23 . A connector  52  may be provided for as a means for routing a data signal from sensor  50  to a transmitter  54  configured for wirelessly transmitting the data signal to a transceiver  56 . Connector  52  may be one or a plurality of electrical leads for conducting a signal from sensor  50  to a surface mounted transmitter  54 . Alternate embodiments allow for various types of connectors  52  to be used as a means for routing a data signal from sensor  50  to transmitter  54 , depending on the specific application. For example, one or a plurality of fiber optic connectors may be used for routing a signal using single or varying wavelengths of light. 
     Embodiments allow for transmitters  54  to be multi-channel and have various specifications depending on their location within a casing of combustion turbine  10 . Transmitters  54  may be configured to function within the compressor  12  casing subject to operating temperatures of between about 80° C. to 120° C. They may also be configured to function within the turbine  12  casing subject to operating temperatures of between about 300° C. to 350° C. of higher, and be resistant to oxidative exposure. 
       FIG. 3  illustrates a schematic plan view of compressor vane  23  having sensor  50  connected therewith and connector  52  connecting sensor  50  with transmitter  54 . A power source  51  may be provided, such as an appropriately sized battery for powering transmitter  54 . In alternate embodiments transmitter  54  may be located remotely from vane  23  and powered from an external power source. Transmitter  54  may receive signals from sensor  50  via connector  52  that are subsequently wirelessly transmitted to transceiver  56 . Transceiver  56  may be mounted on hub  58  or on a surface external to compressor  12  such as the exemplary locations shown in  FIG. 1 . Transceiver  56  may be mounted in various locations provided it is within sufficient proximity to transmitter  54  to receive a wireless data transmission, such as an RF signal from transmitter  54 . Transceiver  56  may transmit the RF signal to antenna  32  of system  30  where the signal may be processed for monitoring the condition of compressor vane  23 . 
     With respect to  FIGS. 2 and 3 , one or more sensors  50  may be connected with one or more compressor vanes  23  by fabricating sensor  50  directly onto a surface of vane  23 . Connector  52  may be deposited directly onto a surface of vane  23 . In alternate embodiments a trench or recess may be formed within a surface of vane  23  that is sized for receiving a deposited sensor  50  and connector  52 . Sensor  50  and connector  52  may be deposited within the recess and protected by depositing a coating of suitable material onto a surface of vane  23  over sensor  50  and connector  52 . In other alternate embodiments a coating may be deposited onto a surface of vane  23 , a trench may be formed within the coating and sensor  50  and connector  52  may be deposited within the trench. A protective coating may be deposited over sensor  50  and/or connector  52 . 
     Connector  52  may extend from sensor  50  to a termination location, such as the peripheral edge of vane  23  so that a distal end  53  of connector  52  is exposed for connection to transmitter  54 . Sensor  50  and connector  52  may be positioned on vane  23  to minimize any adverse affect on the aerodynamics of vane  23 . 
     In an embodiment, one or more sensors  50 , such as strain gauges or thermocouples, for example, may be deposited on one or more turbine or compressor blades  18 ,  19 .  FIG. 4  illustrates an embodiment with respect to compressor  12 . A connector  52  may be deposited to connect each sensor  50  to one or more transmitters  54  connected with blade  18 ,  19 . It will be appreciated that exemplary embodiments allow for a plurality of sensors  50  to be connected with a single transmitter  54  via respective connectors  52 . For example, a sensor  50  may be deposited on each of a plurality of blades  18 ,  19 . A connector  52  may be deposited to route a signal from each sensor  50  to a single transmitter  54 . 
     Transmitter  54  and a rotating antenna  55  may be mounted proximate the root of blade  18 ,  19 . Connector  52  may be routed from sensor  50  aft to the root of blade  18 ,  19  to connect sensor  50  with rotating antenna  55 , which may in turn be connected with transmitter  54  via a connector  52   a . A stationary antenna  57  may be installed on a turbine or compressor vane  22 ,  23  aft of the root of respective blade  18 ,  19 . A lead wire  57   a  may be routed from stationary antenna  57  out of compressor  12  or turbine  16  to broadcast a signal to system  30 . In exemplary embodiments, such as that shown in  FIG. 4 , power may be generated through induction during operation of compressor  12  as will be appreciated by those skilled in the art. In this arrangement, transmitter  54  may transmit data to stationary antenna  57  via rotating antenna  55  and power may be supplied from stationary antenna  57  to transmitter  54 . 
     It will be appreciated by those skilled in the art that one or more sensors  50  may be mounted to, such as by a spray deposition, each compressor blade  19  within a row of blades  19  mounted on a disk within compressor  12 . A respective connector  52  may connect each sensor  50  to a respective transmitter  54  mounted proximate the root of each blade  19  within the row. Rotating antenna  55  may encircle the disk proximate the root of each blade  19  and be connected with each transmitter  54  via a respective connector  52   a . One or more stationary antennas  57  may be installed on a compressor vane  23  aft of the row of compressor blades  19 , or in another location, such as a compressor hub sufficiently proximate to rotating antenna  55  for signal broadcasting and receiving. Stationary antenna  57  may also encircle the row of blades  19 . Rows of blades  18  in turbine  16  may be similarly configured. 
       FIG. 5  illustrates a partial view of a component, such as a vane  22  from turbine  16  having a barrier coating  26  deposited thereon. Sensor  50  and connector  52  may be embedded beneath an upper surface of barrier coating  26 . Connector  52  may have a distal end  53  that is exposed at a termination location, such as proximate a peripheral edge  59  of vane  22  for connection with transmitter  54 . In an embodiment transmitter  54  may be surface mounted to vane  22  or embedded within coating  26  proximate peripheral edge  59 . Alternate embodiments allow for transmitter  54  to be located elsewhere such as on a platform (not shown) to which vane  22  is connected or in a cooling flow channel, for example, as will be recognized by those skilled in the art. 
       FIG. 6A  illustrates a schematic plan view of a blade  18  having an exemplary sensor  50  connected therewith and connector  52  connecting sensor  50  with transmitter  54 . Transmitter  54  may be powered through induction generated within turbine  16  during operation that will be appreciated by those skilled in the art.  FIGS. 6A ,  6 B and  6 C illustrate exemplary embodiments of a turbine blade  18  having transmitter  54  placed in various locations. In  FIGS. 6A and 6B  transmitter  54  may be mounted to blade  18  and  FIG. 5C  illustrates that transmitter  54  may be located remote from blade  18 . For example, transmitter  54  may be located remotely from blade  18  such as within a disk (not shown) to which a plurality of blades  18  is attached. In this respect, transmitter  54  may be maintained in a cooler location outside the hot gas path, which may increase the transmitter&#39;s useful life. Locating transmitter  54  remote from blade  18  allows for using an external power source for powering transmitter  54  rather than using a battery or induction. 
     A power supply may also be attached to sensor  50  to provide additional functionality to the sensor. This additional functionality could include mechanical actuation as a result of feedback to the sensor  50  output. Such an integrated system may be applicable for components, such as ring segments for real-time gap control. 
     The exemplary embodiments of compressor vane  23  and turbine blade  18  illustrated in  FIGS. 3-6A ,  6 B and  6 C configured with self-contained sensors  50  and connectors  52  are advantageous in that they may be prefabricated for installation in combustion turbine  10  by a field technician. Embodiments allow for a distal end  53  of connectors  52  to be exposed at a termination location. This location may be proximate a peripheral edge of a component or other location. This allows a field technician to quickly and easily connect connector  52  to a transmitter  54  regardless of its location. 
     Providing components of combustion turbine  10 , such as vanes  23  and/or blades  18  with pre-installed sensors  50  and connectors  52  is a significant advantage over previous techniques for installing such components in the field, which typically required an extensive array of wires to be routed within combustion turbine  16 . Providing components with pre-installed sensors  50  and connectors  52  allows for monitoring the condition of those specific components during operation of combustion turbine  10 . 
     Embodiments of the invention allow for sensor  50  to be configured to perform a wide range of functions. For example, sensor  50  may be configured to detect wear of a single component or between two components, measure heat flux across a component&#39;s coating, detect spalling of a coating, measure strain across an area of a component or determine crack formation within a component or coating. U.S. patent application having application Ser. No. 11/018,816 discloses embodiments of a system that generally involves monitoring the wear of a component that may be configured in accordance with embodiments of the present invention. 
     Wear sensors  50  may be configured as embedded electrical circuits in a contact surface of a component, such as a tip of blade  18  and the circuit may be monitored by monitoring system  30  for indications of wear. By positioning a circuit at the wear limit, or at prescribed depths from the component&#39;s surface, the condition of the surface may be continuously monitored and system  30  may provide an operator with an advanced warning of service requirements. 
     It will be appreciated that sensor  50  may be configured for wear detection and prefabricated within a component for use within combustion turbine  10  either alone or in combination with a means for transmitting  52  in accordance with aspects of the present invention. In this respect, the signals extracted for detection of wear may be conducted via connectors  52  to transmitter  54 , which may transmit the signals via wireless telemetry to a transceiver  56  and subsequently system  30 . 
     Embodiments of the present invention allow for monitoring and control system  30  to collect and store historical data with respect to a component&#39;s wear and correlating the component&#39;s wear with the operating conditions of combustion turbine  10  responsible for producing the wear. This may be accomplished by continuously interrogating turbine  16  conditions, for example, by the deposition of piezoelectric devices and/or other sensors  50  configured for providing a continuous data stream indicative of the loading conditions and vibration frequency experienced by various components within turbine  16 . This data may be correlated to data indicative of a component&#39;s wear and used for predictive maintenance or other corrective actions. 
       FIG. 7  illustrates another exemplary embodiment of a sensor  50  that may be configured as an exemplary heat flux sensor  61  for measuring heat flux across a barrier coating such as a thermal barrier coating (TBC)  60 , which may be yttrium-stabilized zirconium. Using known techniques, thermal barrier coating  60  may be deposited on a bond coat  62 , which may be deposited on a substrate  64 . Substrate  64  may be various components such as a superalloy suitable for use in turbine  16 , and in an embodiment may a blade  18 . The heat flux may be used to obtain the surface temperature of substrate  64  without having to expose the surface of substrate  64  to the surface temperature experienced by the upper surface of thermal barrier coating  60 . 
     Thermocouples  66  may comprise a material having a coefficient of thermal expansion that substantially matches that of the material within which they are deposited, such as thermal barrier coating  60 . In an embodiment, a plurality of temperature sensors, such as K-type thermocouples  66  may be embedded within a thermal barrier coating  60  with thermocouples  66  located vertically over each other as shown in  FIG. 6 . In an embodiment, thermocouples  66  may include a NiCr/NiAl thermocouple junction. Alternate embodiments allow for thermocouples  66  to be fabricated of other materials such as Pt and Pt—Rh for high temperature applications such as those within turbine  16 . 
     Heat flux sensor  61  may be formed in different geometries to achieve a desired signal-to-noise ratio. Each thermocouple  66  may be approximately 25 microns thick but this thickness may vary depending on the application. Because the thermal barrier coating  60  may be several times as thick as thermocouples  66  they will not significantly alter the profile or performance of thermal barrier coating  60 . Embodiments allow for post deposition laser micromachining to achieve a desired junction density. 
     As heat flows vertically into or out of thermal barrier coating  60 , each thermocouple  66  will record a different temperature measurement. By measuring the temperature differences and knowing the thickness and thermal conductivity of thermal barrier coating  60 , the heat flux can be obtained. Thermocouples  66  may be connected with a means for transmitting  52  as described herein so that the respective temperature measurements taken by each thermocouple  66  may be wirelessly transmitted to monitoring and control system  30 . 
       FIGS. 8 and 9  illustrate an exemplary embodiment of a sensor  50  that may be configured as an exemplary sensor  68  configured for detecting and/or measuring strain or a crack within a location of interest such as substrate  70 . For example, substrate  70  may be a location of interest of a surface area of a blade  18 , or it may be other locations of interest within or at the surface of thermal barrier coating  60  or bond coat  62 . It will be appreciated that sensor  68  configured in this manner may be used in numerous places throughout combustion turbine  10 . The sensors described in  FIGS. 8 and 9  describe the utilization of the change in resistance to result in a strain output. Other embodiments of strain gauges could also include capacitive changes to determine the local strain values. 
     In this respect, critical engineering components, such as blades  18 ,  19  and vanes  22 ,  23  are nearly universally subjected to some form of mechanical and/or thermo-mechanical cyclic loading. Aspects of the invention allow for the assessment of component service life by the intermittent or continuous, in-situ measurement of applied strains and crack detection with respect to that component. This may be accomplished by the placement of embedded strain gages and crack sensors  68  in various locations within combustion turbine  10 . Sensors  50  configured as a strain gauge  68  may be formed using a NiCr material for use in lower temperature applications, such as in compressor  12  of combustion turbine  10 . 
     Sensors  68  may be used as crack sensors by placing them at locations or points where cracks are known or likely to appear. A crack sensor gauge  68  may be optimized for size, crack propagation, and crack extent through appropriate choice of gauge  68  parameters. Such parameters may include the footprint of gauge  68 , spacing of fingers  72 , and orientation of fingers  72  with respect to the direction of a predicted crack propagation. Crack formation in substrate  70  gives rise to a large, abrupt change in the strain gauge response, and may be detected by continuously monitoring the sensor  68  output for abrupt signal changes using known signal processing techniques. Data indicative of the signal change may be conducted via a means for transmitting  54  to a transceiver  56  and subsequently transmitted to monitoring and control system  30  via wireless telemetry. 
     In an exemplary embodiment, a strain gauge sensor  68  may be bonded to or deposited on a surface of a compressor blade  19  and positioned so that bending stress on blade  19  varies the output signal from sensor  68 . Connector  52 , which may be wire leads, are routed to a transmitter  54  located on a rotating collar internal to compressor  12 . Transmitter  54  may have an onboard bridge completion and provide a regulated voltage to sensor  68 . As the output signal from sensor  68  varies an RF signal from transmitter  54  varies proportionally. The RF signal may be transmitted to a transceiver  56 , which receives the RF signal and converts it into a voltage signal proportional to the strain detected by sensor  68 . The RF signal may be transmitted to system  30 . An exemplary transmitter  54  may pick up changes in strain from about 30 Hz to about 30 KHz. 
     Embodiments of the invention allow for using crack sensors  68  to monitor crack growth during operation of combustion turbine  10  and verify design models by varying component operating parameters until cracks are detected with the crack sensors  68 . The design models will be calculated for the same operating parameters to see if they successfully predict crack growth and formation, and will be modified accordingly. 
     Monitoring and control system  30  may collect and store data indicative of strain and crack measurements from numerous components in critical locations within combustion turbine  10 , such as blades  18 , for example. Such data may be analyzed over time to develop a strain history for each component. A component&#39;s strain history may include the magnitude and orientation of strains, and the occurrence of overloads under cyclic loading. An appraisal of fatigue damage may be developed and used for predictive maintenance. 
     Embodiments of the present invention allow for deploying a plurality of sensors  50  throughout combustion turbine  10  by either surface mounting them to components or embedding them within respective component barrier coatings to collect specific component condition data and transmit that data using wireless telemetry to monitoring and control system  30 . This approach is advantageous in that it allows for the replacement, repair and maintenance decision-making processes to be based on the condition of specific components during operation of combustion turbine  10 . 
     In this respect, specific component condition data may be received by antenna  32  and receiver  33  then stored in database  36  by CPU  34 . Embodiments allow for specific component condition data to be collected and presented to an operator in real time via display  38 . This allows for an operator to make instantaneous decisions regarding the operation of combustion turbine  10  in response to the condition of a specific component or components. 
     Historical data may be compiled and analyzed with respect to each component for making repair, replacement or maintenance decisions with respect to that component. Operating conditions and specific components of combustion turbine  12  may be monitored sets of conditions may be isolated that are indicative of a component or components needing to be repaired or replaced, or of corrective action to be taken with respect to operation of the gas turbine. These aspects allow for significant improvement in predictive maintenance schedules. 
       FIG. 10  is a partial perspective illustration of a component  110  formed of a substrate material  112  having a barrier coating such as a layer of thermal barrier coating  114  disposed on one surface  116 . The component  110  may be part of a gas turbine engine  10  of  FIG. 1 , for example, or any other machine wherein a base material must be protected from an external environment by a layer of a barrier material. In an embodiment, component  110  may be an airfoil member, such as a turbine blade  18  disposed in the hot gas flow path of a engine  10  with an oxide or non-oxide ceramic TBC  14  such as mullite, silicon carbide or a zirconium-based ceramic overlying a superalloy substrate material  112 . 
     Component  110  may alternatively be fabricated from a ceramic matrix composite (CMC) substrate coated with an environmental barrier coating (EBC) or a thermal barrier coating (TBC). Because the integrity of the coating  114  is critical to the overall integrity of the component  110 , it is useful to obtain operating parameter information that directly affects the performance of the coating  114 . Such information is obtained by embedding a sensor, such as a sensor  50  below the exposed surface  118  of the TBC  114 . The sensor is not visible in  FIG. 10  but may be located below surface  118  in the sensing location indicated generally by numeral  120 . 
     The sensor may be one that provides a signal indicative of temperature, strain, crack initiation, chemical changes, vibration, pressure or other parameters of interest. These sensors themselves could be multi-layered containing a combination of electrodes and the functional body. Conductors  122  may also be located below surface  118  may route the signal produced by the sensor away from sensing location  120  to a termination location, which may be a connection location indicated generally by numeral  224  where they can conveniently exit the component  110 . Conductors  122  may function similarly to connectors  52  for routing a signal from a sensor, such as a sensor  50  to a transmitter  54  for transmission to system  30  via wireless telemetry. The sensor and the conductors  122  may be insulated from the surrounding environment by a layer of insulating material  126 . 
       FIG. 11  is a partial cross-sectional view of another component  130  having a substrate material  132  covered by a barrier coating such as a layer of a thermal barrier coating material  134  for use in a very high temperature environment. As is well known in the art of TBC coatings, a bond coat  136  such as an MCrAlY material may be deposited on the substrate  132  prior to the application of the TBC material  134  to improve the adherence of the coating  134  to the substrate  132 . 
     Component  130  may be instrumented by a plurality of sensors, such as sensors  50  embedded at a plurality of depths below a surface  138  of the TBC material  134  that is exposed to the external environment. A first sensor  140  is deposited in a relatively shallow trench  142 . Trench  142  may be lined with an electrically insulating coating  144  such as aluminum oxide to prevent the grounding of sensor  140  to the TBC material  134 . Sensor  140  may take any form known in the art, for example a thermocouple formed by a bimetallic thermocouple junction or other sensors described herein. The surface location of sensor  140  suggests that it may be useful for sensing a parameter related to the external environment, such as temperature or a chemical parameter. 
       FIG. 12  illustrates the steps of a process  150  that may be used during the manufacturing of the component  130  of  FIG. 11 . In step  152 , a layer of thermal barrier coating material  134  may be deposited onto a substrate  132 . After step  152 , the component is completed in its normal operating shape as it may be used without embedded instrumentation. One skilled in the art may appreciate, therefore, that the process  150  may be applied to newly fabricated components or it may be back fit to an existing component that is in inventory or that has been in service. 
     In step  154 , a trench  142  may be formed in a surface  138  of the component  130 . Trench  142  may be formed to any desired shape by any known method, such as by laser engraving trench  142  to have a generally rectangular cross-section with a predetermined width and depth. Variables for such a laser engraving process include spot size, power level, energy density, pulse frequency, and scan speed. These variables together affect the trench width, depth, material removal rate and the cost of manufacturing. Trench  142  may have a constant cross-sectional size and shape along its entire length, or it may vary in size and/or shape from one region to another. For example, in the component  110  of  FIG. 10 , a trench formed in the sensing location  120  may have different dimensions than the trench extending from the sensing location  120  to the connecting location  124 , since the sensor and the conductors  122  may have different geometries. The trench  142  may also be inclined to the surface, i.e. varying in depth along its length, which in some applications may provide improved mechanical integrity within the component. 
     After trench  142  is formed at step  154 , an insulating coating  144  may be applied to the surfaces of the trench  142  at step  56  in order to provide electrical isolation between sensor  140  and TBC material  134 . Insulating coating  144  may be deposited by any known method such as chemical vapor deposition (CVD) to a thickness sufficient to achieve a desired level of electrical isolation. Once the trench  142  is formed at step  154  and insulated at step  156 , the sensor  140  may be formed by depositing the appropriate material or materials into trench  142  at step  158 . Any known material deposition process providing the desired material properties may be used. Such processes are common in the fields of rapid prototyping, thin and thick film deposition, and thermal spraying, and include, for example, chemical vapor deposition, plasma spray, micro-plasma spray, cold spray, electroplating, electrophoretic deposition, HVOF, sputtering, CCVD, sol-gel and selective laser melting. Processes typically used for the fabrication of multi-layer thick film capacitors may also be used, such as the application of pastes and tapes of the desired materials. 
     After the deposition of material, a heat input may be used to sinter the material, thereby increasing the mechanical integrity of the sensor. This can be done either by heating using a flame, plasma, furnace annealing or localized laser energy application. In the selective laser melting (SLM) process, powdered material having a predetermined chemistry may be deposited into the trench and melted with the energy of a laser beam to form the respective portion of the sensor  140  of  FIG. 11  or the interconnecting conductors  122  of  FIG. 10 . For example, to form a thermocouple, platinum powder may be deposited into one portion of trench  142  and solidified by a SLM process. Platinum-rhodium powder may then be deposited into a second portion of trench  142 , either along the trench length or as a second vertical layer, and solidified by a SLM process to contact the platinum material to form the thermocouple junction. 
     Note that the geometry of trench  142  may have a direct effect on the geometry of the sensor  140 . Accordingly, it is possible to affect the operating parameters of sensor  140  or interconnecting conductors  122  by controlling the dimensions of the respective trench  142 . For example, the resistance of a conducting line formed within a trench will be affected by the width of the trench. The laser engraving process of step  154  may be closely controlled to achieve a desired trench geometry. Certain commercially available processes for depositing a conductor onto a flat surface by thermal spraying may not produce the fine features that may be necessary for sensors and conductive lines. Such processes may rely on a subsequent material ablation process to achieve a desired geometry. Because trench  142  provides control of the width of the feature, no such trimming step is needed in the process  150  of  FIG. 12 . 
       FIG. 11  also illustrates a second trench  160  formed in the TBC material  134  to a second depth that is farther below surface  138  than trench  142 . By forming a plurality of trenches  142 ,  160  at a plurality of depths below surface  138 , it is possible to place sensors, such as sensors  50  at more than one depth within the component  130 , thereby further augmenting the available operating parameter data. In the embodiment of  FIG. 11 , trench  160  contains two vertically stacked conducting layers  162 ,  164  separated by an insulating layer  166 . The conducting layers  162 ,  164  may form two portions of a sensor, or two conducting lines for connecting a sensor to a connecting location.  1 As illustrated in  FIG. 12 , the two conducting layers  162 ,  164  may be formed by first depositing conducting layer  162  at step  158 , and then depositing an insulating layer  166  at step  168  using any desired deposition technique, such as CVD. 
     Steps  158 ,  168  are then repeated to deposit conducting layer  164  and insulating layer  174 . The width of these layers is controlled by the width of trench  160  and the thickness of these layers may be controlled as they are deposited to achieve predetermined performance characteristics. For example, the thickness of insulating material  166  will affect the impedance between the two conducting layers  162 ,  164 . Conducting layer  164  is then isolated from the external environment by backfilling the trench  160  with a barrier material such as thermally insulating material  170  at step  172 . Insulating material  170  may be the same material as TBC material  134  or a different material having desired characteristics. Insulating material  170  may be deposited by any known deposition technique, including CVD, thermal spraying, selective laser melting, or selective laser sintering. Selective laser melting and selective laser sintering processes are known in the art, as exemplified by Chapters 6 and 7 of “Laser-Induced Materials and Processes For Rapid Prototyping” by L. Lu, J. Y. H. Fuh, and Y. S. Wong, published by Kluwer Academic Publishers. 
     Additional sensors  176 ,  178  may be disposed at preselected depths within component  130  by forming respective trenches  180 ,  182  to appropriate depths. Trenches  180 ,  182  may be backfilled with insulating material  170  to the level of surface  138  at step  172 . Planarization of surface  138  may be performed at step  184 , if necessary, such as when surface  138  forms part of an airfoil. By forming a trench to a desired depth, a sensor may be embedded to within the TBC material layer  134 , to within the bond coat material layer  136 , to within the substrate material  132 , or to a depth of an interface between any two of these layers. 
     Thus, it is possible to develop actual operating parameter data across a depth of a component or across the depth of the thermal barrier coating. Such data may be useful for confirming design assumptions and for updating computerized models, and it may also be useful as an indicator of damage or degradation of a TBC coating. For example, a sensor  178  embedded below the TBC material  134  may produce a signal indicating a significant temperature rise in the event of cracking or spalling of the layer of TBC material  134 . Alternatively, the detection of a predetermined level of vanadium, sodium or sulfur deposits by an embedded sensor  176  may announce conditions that would give rise to spalling and failure of the TBC coating  134  if the component were to remain in service for an extended period. This process facilitates the placement of sensors at any location on a fully assembled and coated part. Electrochemical sensors on the component surface can play an important role in determining the nature and effect of corrosion products present in the surrounding environment. 
     MEMS sensors or devices typically include microelectronic packaging, integrating antenna structures for command signals into microelectromechanical structures for desired sensing or actuation functions. Silicon and high temperature electro-ceramics, such as GaN, SiC and AlN micromaching as well as others are advanced micromaching technologies that are commonly used to fabricate MEMS devices having dimensions in the sub-millimeter range. This allows for fashioning microscopic mechanical parts out of silicon substrate or on a silicon substrate, making the structures 3-dimensional, which allows for an array of applications. Electronic circuits functioning as transmitters and antennas may also be imprinted on the chips for wireless transmission. The inventors of the present invention have determined that deploying MEMS devices as integral parts of various components and locations of combustion turbine  10  allows for improved monitoring of component and system operating parameters. This allows for improved diagnostics, predictive maintenance and proof of design. Another advantage is prognosis for design, which may use physics-based approaches towards understanding failures. 
       FIG. 13  illustrates a component  200  that may be formed by depositing a first sensor  210  onto a surface of a substrate  212 . Subsequently, a first layer  214  of a barrier coating  216 , such as a CMC abradable coating system disclosed in U.S. Pat. No. 6,197,424, for example, is deposited over the sensor  210 . A second sensor  220  is then deposited over the first layer  214 . A second layer  218  of barrier coating  216  is then deposited, followed by the deposition of a third sensor  222  and third layer  224  of the barrier coating. In this manner, one or more sensors  210 ,  220 ,  222 , which may be various MEMS devices configured for performing various functions may be embedded at a plurality of depths within the confines of a wall of a component  200 . One may appreciate that the same component  200  may be formed with various combinations of MEMS sensors  210 ,  220 ,  222  configured to monitor various types of conditions associated with component  200 . 
     For example, embodiments of the structure of  FIG. 13  may be useful for monitoring various properties of coating  216  such as the amount of wear of an abradable coating system, since each of the sensors  210 ,  220 ,  222  may become exposed at a different time as the coating  216  undergoes wear due to abrasion. Signals generated by the respective sensors  210 ,  220 ,  222  may be responsive to the wear of coating  216  and may be used in an improved clearance control program for predicting the remaining useful life of an abradable coating and/or for estimating the amount of leakage past an abradable seal. 
       FIG. 14  illustrates a schematic plan view of an exemplary MEMS device or sensor  250  that may be affixed to a component&#39;s substrate, such as directly onto a surface of the substrate, using phosphate cement or glue. MEMS device  250  may be affixed beneath the substrate&#39;s surface such as by affixing within an indentation or recess then covered with an over layer of protective coating. It may alternately be affixed to the substrate by being retained within a barrier coating or otherwise properly secured in place for its intended purpose. Embodiments of MEMS sensor  250  may be conductively coupled to leads  258 ,  260 ,  266 ,  268  and conductors  262 ,  264 ,  270 ,  272 , respectively, which may be deposited using thermal spray deposition, for example, such as the conformal direct write technology disclosed in U.S. Pat. No. 6,576,861. Other deposition processes may be used as recognized by those skilled in the art. 
     A plurality of sensors  250  may be affixed at varying depths within a coating such as an abradable coating system  216 . Thermal sprayed abradable coating systems  216  are typically applied for gas path clearance control, which influences power output and efficiency of combustion turbine  10 . Coating systems  216  are usually porous coatings that abrade when contacted by a moving structural component, such as the tips of blades  18  and are designed not to damage the contacting surface. Information with respect to the wear behavior of coating system  216  may be used to predict the useful life of the coating, prevent catastrophic interaction between components and allow for improved control of combustion turbine  10 . 
     MEMS sensor  250  may be configured as a proximity sensor that operates under capacitance or inductance. Sensor  250  may be an inductive proximity sensor comprising a coil, an oscillator, a detection circuit and an output circuit as recognized by those skilled in the art. The oscillator generates a fluctuating magnetic field around the winding of the coil that locates in the MEMS device&#39;s sensing face. When a metal object moves into the inductive proximity sensor&#39;s field of detection, eddy circuits build up in the metallic object, magnetically push back, and finally dampen the sensor&#39;s  250  own oscillation field. The detection circuit monitors the oscillator&#39;s strength and triggers an output from the output circuitry when the oscillator becomes dampened to a sufficient level. 
     One or more conductive connectors, such as a connector  52  may be provided as a means for routing data signals indicative of the measured response from sensor  250  to a transmitter  54 , which may be configured for wirelessly transmitting the data signal to a transceiver  56 , such as those shown in  FIG. 1 . Connector  52  may be one or a plurality of electrical leads for conducting a signal from sensor  250  via conductors  270 ,  272  to a transmitter such as surface mounted transmitter  54 . Alternate embodiments allow for the signal to be conducted to an antenna (not shown), which may be an inductively couple spiral coil for wirelessly transmitting data signals from sensor  250  to a transmitter  54  and/or transceiver  56 . 
     Exemplary embodiments of MEMS sensor  250  may be configured to produce an eddy current circuit to detect intrusions into abradable coating system  216 . Such intrusions may be the tips of rotating blades  19  in compressor  12  or blades  18  in turbine  16  abrading coating  216  during operation of combustion turbine  10 . Intrusions between other components may be detected within the casing of compressor  12  or turbine  16  at various other places of interest. 
     Embodiments of MEMS sensor  250  may be an inductive proximity sensor having circuitry that generates an electromagnetic field and detects any changes in a resonant circuit caused by eddy current losses induced in a conductive material influencing the magnetic field. When an AC voltage is applied to MEMS sensor  250  an oscillating current radiates an electromagnetic field. When an electrical conductor or metal component such as a tip of blade  18 , for example, enters the electromagnetic field, eddy currents are drawn from the oscillator and induced into the blade tip. The losses in energy caused by the eddy currents may be correlated to the distance and position of the blade tip relative to MEMS sensor  250 . 
       FIG. 15  is a partial perspective view of turbine blades  18  intruding into abradable coating system  216  during rotation of the blades such as when combustion turbine  10  is in operation. A plurality of blades  18  is mounted to a rotor disk  280 . Blade tips  282  are located just inside an inner wall  284 , which may be a blade outer air seal or ring segment of combustion turbine  10  as recognized by those skilled in the art. Abradable coating system  216  may be deposited on a ring segment  284  so that a groove  286  is abraded within the coating as blades  18  rotate. One or more MEMS sensors  250  may be affixed on or within the inner surface of ring segment  284 , or within abradable coating system  216 . 
     MEMS sensors  250  are depicted schematically as boxes in  FIG. 15  but it will be appreciated they may be configured to perform various functions and be affixed in various configurations, orientations and locations. Embodiments of the invention may be used for continuously measuring the distance between blade tip  282  and one or more MEMS sensors  250  during operation of combustion turbine  16 . In this aspect, a first distance between the end of a blade tip  282 , or other selected locations on a blade  18 , and the location of one or more MEMS sensors  250  is known. The first distance may be calculated and stored in database  36  of monitoring system  30  and may be the distance between a blade tip  282  and a MEMS sensor  250  prior to the commissioning of a combustion turbine  10 . The first distance may be other distances depending on the desired measurements to be taken. It will be appreciated that blade tip  282  may be coated with a barrier coating such as TBC  26  ( FIG. 1 ). The composition and thickness of such a coating may be accounted for when selecting a location for one or more MEMS sensors  250  and calculating wear of coating system  216 . 
     Abradable coating system  216  has a first or original thickness when initially deposited on ring segment  284 , or after repairing the coating, and prior to being abraded by blade tips  282 . One or a plurality of MEMS sensors  250  may be affixed within coating system  216  at varying selected depths from the original surface  288  of coating system  216 . For instance, a plurality of MEMS sensors  250  may be affixed in spaced relation around the circumference of ring segment  284  for taking a respective plurality of measurements with respect to a single row of blades  18 . Ring segment  284  may include a row of ring segment sections that circumscribe the row of blades. Using MEMS sensors  250  is advantageous because a large quantity may be affixed in an area of interest to ensure data extraction in the event one or more sensors fail. 
     As blade tips  282  of the row of blades  18  abrade coating system  216 , groove  286  is formed within coating  216  that is approximately the width of blades  18 . Blades  18  abrading coating  216  forms a second or operating thickness of that portion of coating system  216  that is not worn away by blade tips  282 . This operating thickness may be defined as the thickness of coating system  216  from the surface of groove  286  to the interface  283  of coating system  216  with ring segment  284 . The operating thickness may vary around the circumference of a respective ring segment  284  as appreciated by those skilled in the art. 
     The plurality of MEMS sensors  250  may continuously transmit data to monitoring system  30  indicative of the distance between a respective sensor  250  and a respective blade tip  282 . Data indicative of the distances blade tips  288  have traveled into coating  216  may be stored in database  36 . This data may be used by processor  34  to calculate the amount or depth of wear the abradable coating system  216  is experiencing around the circumference of ring segment  284 . In this respect, processor  34  may calculate the distance one or more blade tips  282  have traveled into coating system  216  during operation of combustion turbine  10  such as when going from start-up to full load. 
     Processor  34  may calculate the size of gaps formed between a blade tip  282  and the inner surface of groove  286 , including its edges, such as gaps formed when a blade tip  282  contracts from its maximum incursion into coating system  216 . Such gaps may be calculated knowing the original thickness of coating  216 , the maximum incursion of blade tips  288  into coating  216  and the current distance between MEMS sensors  250  and blade tips  288 . This allows for estimating secondary gas path flow past through the gaps, which may be used for more efficient operation of combustion turbine  10  and improved predictive maintenance. Calculations made by processor  34  based on data from MEMS sensors  250  may be related to operating cycles of combustion turbine  10  for various purposes including improved control during operating, cooling and service cycles of combustion turbine  10 , and avoidance of catastrophic failure. 
     Components within compressor  12  and turbine  16  may have different rates of thermal expansion so they expand and contract at different rates during heating and cooling of turbine  16 . Blades  18  may expand more quickly than a rotor to which rotor disk  280  is mounted due to differences in their shape and mass. A control module of system  30  may use real-time and historical data from MEMS sensors  250  during operation or a heating and/or cooling cycle of turbine  16  to prevent blade tips  282  from impinging on the inner surface of ring segment  284  by controlling various operating parameters of combustion turbine  10 . For example, the turbine engine ramp rates and shut down schedule as well as scheduled spin cool cycles may be controlled in response to data received from MEMS sensors  250 . 
     This data may also be used to control combustion turbine  10  to avoid other “pinch points”, which may occur between numerous components within compressor  12  or turbine  16  during heating and/or cooling cycles. Such “pinch points” may develop for numerous reasons such as distortion of ring segment  284  due to servicing, uneven wear around ring segment  284 , or the encroachment of ring segment  284  toward blade tips  282 . This may happen due to vibration-induced wear on the hook portions of the ring segment holding it in place within an isolation ring. 
     Aspects of the invention allow for using various embodiments of MEMS sensors  250  to directly interrogate components and coatings within combustion turbine  10  to acquire data indicative of information that is a function of the type of MEMS sensor used. MEMS devices configured to perform more than one function may also be used.  FIG. 14  is a schematic of a MEMS device  250  that may be configured to perform various functions such as an accelerometer, for example, that may be used to measure vibration. An exemplary MEMS accelerometer  250  may consist of a proof mass suspended by a spring such as a cantilever or beam. When MEMS accelerometer  250  is subjected to acceleration, the inertia of the mass causes changes in the gap between it and the bulk of the device. The principle of measuring the gap between the mass and bulk of the device can be performed using a capacitive, piezoresistive, piezoelectric, thermal, resonance or surface acoustic waves (SAW) principle as recognized by those skilled in the art. 
     In this respect, response data from a MEMS accelerometer  250  may be analyzed by monitoring system  30  to determine vibration frequency, forces and displacement of components within combustion turbine  10 . This information may be used in assessing operating conditions of combustion turbine  10  including setting air and fuel maps during commissioning, monitoring for wear as a result of service, evaluating combustion dynamics, evaluating components for changes in natural frequency, which may be indicative of cracks or other defects, and validation of design methodologies. 
     Embodiments of MEMS sensor  250  may be configured to perform other functions such as a load cell, pressure transducer, strain gauge, or temperature and heat flux sensors, for example, as recognized by those skilled in the art. A MEMS load cell  250  may include two bonded silicon wafers where the bottom layer contains an electrode pattern forming an array of capacitors with the top wafer acting as a common electrode. The load may be estimated through a change in capacitance between the flexible electrode and the rigid electrode. MEMS load cell  250  may be used to assess boundary conditions between components. Specifically, both static and dynamic contact force between two components may be measured. Such measurements may be used by monitoring system  30  to assess surface bearing stresses, critical in the prevention of wear, as well as providing feedback for calibration and validation of design methodologies and boundary conditions. 
     Embodiments allow for using MEMS pressure sensors  250 , such as those in the two general classes of: (a) piezoresistive where a silicon diaphragm consisting of a few resistors in a Wheatstone bridge configuration allows for sense changes in pressure through changes in resistance; and (b) capacitive where the capacitance between a flexible membrane and a fixed plate changes as a function of pressure. MEMS pressure transducers  250  may be deployed in various places within combustion turbine  10  such as the engine inlet for measurement of pressure distribution or detection of inlet pressure instabilities. Also, using MEMS pressure sensors  250  for sensing between stages of compressor  12  allows for detecting rotating stalls and early surge detection. This data may be used by monitoring system  30  for controlling operation of combustion turbine  10 . 
     Embodiments allow for using MEMS devices  250  configured as strain gauge, temperature and heat flux sensors that may be based on the principles disclosed in “Microsensors, microelectromechanical systems (MEMS), and electronics for smart structures and systems” by V. K. Varadan and V. V. Varadan published by IOP Publishing LTD, United Kingdom. Such MEMS devices  250  may utilize the surface acoustic wave (SAW) properties of materials to measure static and dynamic strain, and the thermoelectric properties of the materials to measure temperature and heat flux. A SAW is typically a piezoelectric wafer such as lead zirconium titanate (PZT) and lithium niobate (LiNbO 5 ) class of materials, with interdigital transducers (IDT) and reflectors on its surface. The IDT converts electrical energy into mechanical energy and vice versa for generating and detecting SAW. The temperature and strain sensitive properties of the above class of materials may further be taken advantage of in measuring temperature and heat flux. 
     Embodiments of MEMS devices  250  configured as strain gauges, temperature and heat flux sensors may be deployed in various places within combustion turbine  10 . For example, MEMS strain sensors  250  may be affixed on blades  18 ,  19  in compressor  12  and turbine  16  for measuring static and dynamic strains. MEMS temperature and heat flux sensors  250  may be utilized on blades  18  and vanes  22  in turbine  16  for measuring component thermal state, such as hot spots, cooling effectiveness, thermal efficiency and heat flux transients within the component or coating. This allows for an improved understanding of thermal environments in turbine  16  for materials development and design validation. 
     MEMS sensors  250  may be embedded directly into the surface of a component or frame of combustion turbine  10  as well as within coatings deposited on the component or frame. The MEMS sensors  250  may be insulated from the surrounding component or frame via an insulating layer of material that may be deposited by thermal spray or other techniques. Appropriate electrical connections may be made using conventional wires or conductive leads deposited by microplasma spray technology or other techniques such as ones described herein. Over layers of coatings may be deposited as necessary such as ones for wear resistance, dimensional control, oxidation resistance and thermal barriers. 
     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.