Vibration sensor

A sensor includes a housing adapted to be secured to a component within a system to be monitored by the sensor, an optical fiber, and a membrane spring assembly. The optical fiber includes a sensing portion containing a fiber Bragg grating that is able to undergo expansion and contraction resulting from movement of the optical fiber at a second location relative to a first location. The membrane spring assembly includes a membrane disc, wherein movement of a central portion thereof causes corresponding displacement of the optical fiber at the second location to cause expansion and contraction of the sensing portion of the optical fiber containing the fiber Bragg grating, which expansion and contraction effects a change in a light wavelength reflected by the fiber Bragg grating. The light wavelength reflected by the fiber Bragg grating can be used to measure movement of the central portion of the membrane disc.

FIELD OF THE INVENTION

The present invention relates to a vibration sensor, and more particularly, to a vibration sensor including an optical fiber containing a fiber Bragg grating.

BACKGROUND OF THE INVENTION

An electrical generator used in the field of electrical power generation includes a stator winding having a large number of conductors or stator bars that are pressed into slots in a base body, in particular, a laminated stator core or a rotor body. Such an electrical generator represents a very expensive and long-term investment. Its failure not only endangers the power equipment itself but may also result in very severe service reduction due to the down time associated with repair.

To avoid such a condition, diagnostic systems have been developed for early identification of defects. Due to the very high voltages within the generator, diagnostic systems for generators typically use sensor technology that avoids electrically conducting wires that could cause arcing to ground if they are deployed on a structure that is at a high voltage. For example, sensing signals within generators have been conveyed by optical conductors, such as by glass fibers.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, a sensor is provided comprising a housing, an optical fiber, and a membrane spring assembly. The housing is adapted to be secured to a component within a system to be monitored by the sensor. The optical fiber is secured within the housing at a first location that is fixed relative to the housing and at a second location that is movable relative to the housing such that a sensing portion of the optical fiber between the first and second locations is able to undergo expansion and contraction resulting from movement of the optical fiber at the second location relative to the first location. The sensing portion of the optical fiber contains a fiber Bragg grating. The membrane spring assembly is located in the housing and comprises a membrane disc having a fixed portion that is fixed relative to the housing and a central portion that is movable relative to the housing. The central portion is fixed relative to the optical fiber at the second location such that movement of the central portion causes corresponding displacement of the optical fiber at the second location to cause expansion and contraction of the sensing portion of the optical fiber containing the fiber Bragg grating. The expansion and contraction of the sensing portion of the optical fiber effects a change in a light wavelength reflected by the fiber Bragg grating. The light wavelength reflected by the fiber Bragg grating can be used to measure movement of the central portion of the membrane disc.

In accordance with a second aspect of the present invention, a sensor system is provided comprising a sensor. The sensor comprises a housing, a membrane spring assembly, and an optical fiber. The housing is adapted to be secured to a component within a system to be monitored by the sensor system. The membrane spring assembly is located in the housing and comprises a membrane disc and first and second height discs. The membrane disc has a fixed portion that is fixed relative to the housing and a movable portion that is movable relative to the housing. The first and second height discs are located on opposing sides of the membrane disc and limit a maximum displacement flexure of the movable portion of the membrane disc. The optical fiber is located within the housing and comprises a first portion that is fixed relative to the housing, a second portion containing a fiber Bragg grating, and a third portion that is fixed relative to the movable portion of the membrane disc. The second portion of the optical fiber is located between the first and third portions thereof such that the second portion containing the fiber Bragg grating is able to undergo expansion and contraction resulting from movement of the movable portion of the membrane disc relative to the housing. The expansion and contraction of the second portion of the optical fiber effects a change in a light wavelength reflected by the fiber Bragg grating. The light wavelength reflected by the fiber Bragg grating can be used to measure movement of the movable portion of the membrane disc.

In accordance with a third aspect of the present invention, a sensor system is provided comprising a sensor. The sensor comprises a housing, a membrane spring assembly, and an optical fiber. The housing is adapted to be secured to a component within a system to be monitored by the sensor system. The membrane spring assembly is located in the housing and comprises a membrane disc and first and second membrane stoppers. The membrane disc has a fixed portion that is fixed relative to the housing and a movable portion that is movable relative to the housing. The first and second membrane stoppers are located on opposing sides of the membrane disc and limit a maximum displacement flexure of the movable portion of the membrane disc. The optical fiber is located within the housing and comprises a first portion that is fixed relative to the housing, a second portion containing a fiber Bragg grating, and a third portion that is fixed relative to the movable portion of the membrane disc. The second portion of the optical fiber is located between the first and third portions thereof such that the second portion containing the fiber Bragg grating is able to undergo expansion and contraction resulting from movement of the movable portion of the membrane disc relative to the housing. The expansion and contraction of the second portion of the optical fiber effects a change in a light wavelength reflected by the fiber Bragg grating. The light wavelength reflected by the fiber Bragg grating can be used to measure movement of the movable portion of the membrane disc.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a portion of a stator10for an electric generator is illustrated and includes a stator core12comprising a plurality of stator teeth14defining radially extending slots16. The stator core12comprises stator coils18including one or more stator bars20located in each slot16. In the illustrated embodiment, a pair of stator bars20is located in stacked relation within each slot16. The stator bars20may be wrapped in an insulation layer (not shown) forming a ground wall insulation.

The bars20may be retained in position by a retention structure24comprising one or more filler members, such as top slot fillers26and a top ripple spring28placed in the slot16radially inwardly from the inner one of the stator bars20. The retention structure24may further comprise a wedge30installed in the slot16, located radially inwardly from the top ripple spring28, to compress the stator bars20in the slot16with a predetermined tightness and to substantially limit movement of the bars20relative to the stator core12. While the position of the pair of stator bars20is substantially maintained by the retention structure24, a certain degree of bending movement of the stator bars20still occurs in response to vibrations within the generator, causing stress in the material of the bars20.

Referring additionally toFIG. 2, a vibration sensor50according to an embodiment of the invention is mounted to a select one of the stator bars20′ and is illustrated inFIG. 1as being mounted to an end portion20A of the select stator bar20′. It is noted that additional stator bars20of the stator core12may include additional vibration sensors50. It is further noted that the vibration sensor50may be mounted to the select stator bar20′ at locations other than the end portion20A thereof, such as a top portion20B or a side portion20C thereof (seeFIG. 1).

In accordance with the present invention, vibrations of the select stator bar20′ and a condition of the vibration sensor50, i.e., a structural condition, may be monitored via a signal provided by the vibration sensor50. That is, the vibration sensor50provides a signal comprising sensor data, wherein the sensor data is monitored to determine vibrations of the select stator bar20′ and also to determine the condition of the vibration sensor50in accordance with an embodiment of the invention, as will be described herein. The signal provided by the vibration sensor50comprises a dynamic measurement signal of substantially cyclically varying value and is indicative of a stress level in the stator bar20. In particular, the measurement signal may comprise a displacement signal that may be differentiated once to provide data on velocity and differentiated twice to provide data on acceleration of the end portion20A of the select stator bar20′.

Referring toFIGS. 2-4, the vibration sensor50comprises a housing52(FIGS. 2 and 4) that contains the internal components of the vibration sensor50, which will be described herein. It is noted that only selected components of the vibration sensor50are illustrated inFIG. 3so as to more clearly illustrate these selected components and to facilitate an effective description of their function.

The vibration sensor50includes a fiber optic sensor comprising a fiber optic Bragg grating (FBG)54defined by an index of refraction grating formed on a fiber optic conductor (FOC)58, seeFIGS. 3 and 4. The refraction gratings of the FBG54are formed at a predetermined spacing to reflect light passing through the FOC58at a predetermined wavelength comprising a grating-specific central Bragg wavelength λ0. The FOC58comprises an elastically deformable material, such as an optical fiber used in conventional Bragg grating sensors and which may expand and contract in response to forces applied on either side of the FBG54. As is described in greater detail below, the FOC58may be connected to a deflectable mass, which may be displaced relative to a frame that is also connected to the FOC58. The displacement of the mass relative to the frame, corresponding to vibrations of the select stator bar20′, may cause a resulting cyclical elastic expansion and contraction of the FOC58, such that a measured wavelength λ of light reflected from the FBG54may vary cyclically about the central Bragg wavelength λ0. The cyclical variation of the measured wavelength λ of light reflected from the FBG54may be monitored and processed in a conventional manner to determine a condition of the generator in the region of the select stator bar20′.

A source of optical radiation56, such as a broadband light source, is coupled to the FOC58at a coupler60for providing the vibration sensor50with optical radiation, seeFIGS. 2-4. The source of optical radiation56provides a predetermined range of light wavelength (or frequency) to correspond to the reflective response of the central Bragg wavelength λ0of the vibration sensor50. Reflected light from the vibration sensor50is transmitted back through the FOC58and is received via the coupler60at a processor62or spectrum analyzer, as will be described herein.

Referring toFIG. 2, the FOC58enters the housing52through an aperture64formed in a wall of the housing52. As shown inFIG. 3, a first portion58A of the FOC58extends through a bore66A formed through an anchor member66of the vibration sensor50. The first portion58A of the FOC58is secured to the anchor member66at a first location L1(seeFIG. 3) within the bore66A using a suitable affixation procedure, such as, for example, by adhesive bonding or cementing the first portion58A of the FOC58to the anchor member66within the bore66A. The anchor member66extends through an aperture68A formed in an anchor plate structure68and is threadedly affixed to a core support70, seeFIG. 4. The anchor plate structure68is used to define a curvature of the FOC58between a groove69A in a leg69of the anchor plate structure68and the anchor member66and to retain the first portion58A of the FOC58in position. The anchor plate structure68is secured to the core support70via a plurality of bolts72, and the core support70is coupled to a lower section52A of the housing52via a plurality of bolts74, see FIG.2. The core support70structurally supports the anchor plate structure68, the anchor member66, and the first portion58A of the FOC58at the first location L1within the lower section52A of the housing52, such that these components are fixed relative to the housing52.

As shown inFIG. 4, a threaded end portion66B of the anchor member66is threadedly received in a threaded opening70A that is formed through the core support70. The FOC58extends out of the bore66A at the anchor member end portion66B and is received in a bore80A extending through a pointer member80(seeFIG. 3), which pointer member80will be described herein. A second portion58B of the FOC58extending between the anchor member66and the pointer member80is able to undergo expansion and contraction and comprises a sensing portion of the FOC58containing the FBG54described above.

As shown inFIG. 4, a threaded first end portion80B of the pointer member80is threadedly engaged in a threaded hole82A of a first mass82to support the first mass82thereon, and a threaded second end portion80C of the pointer member80is threadedly engaged in a threaded hole84A of a second mass84to support the second mass84thereon. Each of the first and second masses82,84according to one embodiment of the invention weigh about 20-30 grams, although the masses82,84could have other weights depending on the particular configuration of the vibration sensor50and the generator in which is it employed. Additional details in connection with the masses82,84will be discussed herein.

A third portion58C (seeFIG. 3) of the FOC58is secured to the second end portion80C of the pointer member80at a second location L2within the bore80A using a suitable affixation procedure, such as, for example, by adhesive bonding or cementing the third portion58C of the FOC58to the pointer member80within the bore80A. As will be discussed herein, the third portion58C of the FOC58at the second location L2is movable relative to the housing52.

Referring toFIGS. 2-4, a membrane spring assembly90is associated with the pointer member80. As most clearly shown inFIG. 4, the membrane spring assembly90comprises a first membrane stopper92, a first height disc94, a membrane disc96, a second height disc98, and a second membrane stopper100. These components of the membrane spring assembly90are preferably formed from stainless steel and are coupled together via a plurality of bolts102.

The bolts102engage threaded holes104A of a spacer member104to couple the membrane spring assembly90to the spacer member104(seeFIGS. 2 and 4), which spacer member104is coupled to the core support70via a plurality of bolts105. The core support70and spacer member104define a mass-spring support structure107for effectively coupling an outer peripheral portion of the membrane disc96to the housing52, so as to effectively couple the outer peripheral portion of the membrane disc96to the select stator bar20′. That is, the outer peripheral portion of the membrane disc96comprises a fixed portion that is structurally supported within the housing52via the core support70and is fixed relative to the housing52and to the select stator bar20′. The spacer member104is provided to maintain a desired distance between the membrane spring assembly90and the core support70, although the membrane disc96flexes a small amount in the direction of a central axis CAof the vibration sensor50(seeFIG. 2) during operation of the generator corresponding to vibrations transmitted to the vibration sensor50, as will be discussed herein.

As shown inFIGS. 3 and 4, first and second nuts106,108are located between the respective first and second masses82,84and the membrane disc96. The masses82,84and the nuts106,108effectively trap the membrane disc96therebetween and function to couple a moveable (relative to the housing52), central portion of the membrane disc96to the pointer member80through the engagement of the nuts106,108to either side of the central portion. The pointer member80is effectively coupled to the second portion58B of the FOC58containing the FBG54via the coupling of the third portion58C of the FOC58within the bore80A of the pointer member80at the second location L2. Thus, the central portion of the membrane disc96is effectively coupled to the second portion58B of the FOC58containing the FBG54, such that vibratory movement of the select stator bar20′ and corresponding movement of the vibration sensor50and the outer peripheral portion of the membrane disc96cause displacement of the second portion58B of the FOC58containing the FBG54. That is, the central portion of the membrane disc96and the first and second masses82,84are fixed relative to each other but moveable relative to the housing52and form a mass-spring system110(seeFIG. 2). The mass-spring system110is supported to the mass-spring support structure107, where flexing movement of the central portion of the membrane disc96resulting from vibrations transmitted to the housing52from the select stator bar20′ causes corresponding expansion and contraction of the second portion58B of the FOC58containing the FBG54, as will be discussed herein.

The first and second height discs94,98, which are located at opposing sides of the membrane disc96, comprise ring-shaped members defining respective central apertures94A,98A (seeFIG. 4) therein. The first and second height discs94,98effect a damping of vibratory movement of the central portion of the membrane disc96so as to limit the maximum displacement flexure of the membrane disc96, thereby limiting the amount of expansion/contraction of the second portion58B of the FOC58so as to prevent the FOC58from breaking. Specifically, the first height disc94limits the maximum displacement flexure of the central portion of the membrane disc96by restricting movement of the outer peripheral portion of the membrane disc96in a radially inward direction of the sensor50, i.e., in a direction parallel to the central axis CAof the sensor50, to effectively limit the amount of contraction of the second portion58B of the FOC58. Similarly, the second height disc98limits the maximum displacement flexure of the central portion of the membrane disc96by restricting movement of the outer peripheral portion of the membrane disc96in a radially outward direction to effectively limit the amount of expansion of the second portion58B of the FOC58. It is noted that sizes of the apertures94A,98A in the height discs94,98can be modified to control the amount of damping of vibratory movement of the central portion of the membrane disc96that is provided by the height discs94,98.

The first and second membrane stoppers92,100also limit the maximum displacement flexure of the membrane disc96, thereby limiting the amount of expansion/contraction of the second portion58B of the FOC58so as to prevent the FOC58from breaking. Specifically, the first membrane stopper92acts as a physical stop for contacting the central portion of the membrane disc96to restrict movement of the central portion of the membrane disc96in a radially inward direction to effectively limit the amount of contraction of the second portion58B of the FOC58. Similarly, the second membrane stopper100acts as a physical stop for contacting the central portion of the membrane disc96to restrict movement of the central portion of the membrane disc96in a radially outward direction to effectively limit the amount of expansion of the second portion58B of the FOC58.

It is noted that sizes of apertures92A,100A (seeFIG. 4) in the membrane stoppers92,100, and/or the thicknesses of height discs94,98, can be modified to control the limitation of vibratory movement of the central portion of the membrane disc96that is provided by the membrane stoppers92,100. It is also noted that, while the outer peripheral portion of the membrane disc96is fixed relative to the housing52and the central portion of the membrane disc96is movable relative to the housing52, the sensor50could be configured such that the outer peripheral portion of the membrane disc96is movable relative to the housing52and the central portion of the membrane disc96is fixed relative to the housing52. That is, the first and second height discs94,98could trap the central portion of the membrane disc96therebetween while allowing the outer peripheral portion to flex radially. In such a configuration, the outer peripheral portion of the membrane disc96, or a least a portion thereof, could be structurally coupled, either directly or indirectly, to the second portion58B of the FOC58.

Further, while the sizes of the apertures92A,100A in the membrane stoppers92,100are fixed in the embodiment shown, the sizes of the apertures92A,100A could be variable, such that the sizes thereof could be manually or automatically adjusted during operation of the generator to change the maximum displacement flexure of the membrane disc96. This could be accomplished in a manner similar to how a diaphragm mechanism operates in a camera, as will be apparent to those skilled in the art.

In the preferred embodiment, the first and second membrane stoppers92,100are separate components from the height discs94,98. However, it is noted that the height discs94,98may be formed integrally with the respective membrane stoppers92,100, i.e., as stepped components.

During operation of the generator, vibrations or vibratory movement of the select stator bar20′ result in corresponding vibratory movement of the sensor housing52via the attachment of the sensor housing52to the end portion20A of the stator bar20′. The vibratory movements of the sensor housing52are transferred to the mass-spring support structure107via the coupling of the core support70to the lower section52A of the sensor housing52. Since the outer peripheral portion of the membrane disc96is affixed to the mass-spring support structure107, the vibratory movement of the housing52is transmitted to the outer peripheral portion of the membrane disc96. At the central portion of the membrane disc96, inertias of the masses82,84effectively resist movement of the central portion of the membrane disc96and cause the membrane disc96to flex in response to the vibratory movement transmitted to the fixed, outer peripheral portion of the membrane disc96. Thus, the membrane disc96may vibrate at a frequency corresponding to the driving frequency(ies) of the select stator bar20′.

Since the third portion58C of the FOC58is coupled to the central portion of the membrane disc96through the pointer member80, i.e., at the second location L2, and the first portion58A of the FOC58is coupled to the support structure70through the anchor member66, i.e., at the first location L1, displacement of the central portion of the membrane disc96, i.e., caused by the vibrations transmitted to the membrane disc96by the mass-spring support structure107, results in a corresponding expansion and contraction of the second portion58B of the FOC58at a frequency(ies) corresponding to the frequency(ies) of vibration in the select stator bar20′. It is noted that the FOC58is preferably attached to the anchor member66and the pointer member80in a pre-stretched condition. Thus, vibratory movement transmitted to the membrane disc96results in a further expansion or a contraction of the FOC58. It is further noted that this expansion and contraction of the FOC58is very small, i.e., on the order of micrometers. On a macroscopic scale the movement of the membrane disc96and the corresponding movement the FOC58is almost imperceptible, but the resulting expansion and contraction of the FBG54causes a detectable change in the wavelength λ reflected by the FBG54. The variation of the reflected wavelength λ is a direct measurement of the magnitude of expansion and contraction of the FOC58, which is directly related to a displacement of the membrane disc96caused by vibratory movement of the housing52. In this way, the flexing movement of the membrane disc96may be measured and may be used to determine a displacement associated with vibrations of the end portion20A of the select stator bar20′.

Data in the form of reflected wavelengths λ produced at the FBG54may be transmitted back through the FOC58via the coupler60to the processor62. The processor62may process the data, i.e., variations in wavelength λ, on a time dependent basis to determine an acceleration associated with the data. Further, the processor62may determine a frequency of vibration based on the variation of the wavelength with time. In particular, in addition to the data received by the processor62corresponding to the displacement and/or acceleration of the sensor50on the select stator bar20′, the processor62may process the data to identify frequencies of interest, including magnitudes of displacement and/or acceleration at the frequencies of interest. One such frequency of interest corresponds to the natural frequency of the mass-spring system110formed by the membrane disc96and the masses82,84.

In conventional accelerometer sensor designs, it is desirable to design the mass-spring system such that the natural frequency of the mass-spring system is substantially different from the frequencies of the vibrations in the system being monitored by the sensor. In particular, in conventional sensor designs it is common to design the natural frequency of the sensor to be substantially higher than the frequencies of the system to be measured. Providing a substantial difference between the natural frequency of the sensor and the frequencies at which data is collected on the system being monitored makes it unlikely that distortion associated with natural frequency inputs from the sensor will interfere as noise in the collected data.

In accordance with an aspect of the present invention, the natural frequency of the mass-spring system110of the sensor50is designed to be relatively close to the driving frequencies of the system to be monitored. In particular, the system is designed to have a higher sensitivity, which results in a lowering of the natural frequency of the mass-spring system110of the sensor50. For example, for a generator in which the majority of monitored frequencies may comprise harmonic frequencies that are typically less than about 250 Hz, the design of the sensor50may comprise a natural frequency of greater than about 400 Hz, e.g., about 410 Hz. However, it is noted that the design of the vibration sensor50can be altered such that its natural frequency is tailored for use in other types of systems having other frequencies to be monitored. For example, the weight of the first and second masses82,84and/or the size of the central apertures94A,98A of the height discs94,98can be altered to effectively change the natural frequency of the vibration sensor50. Further, the sensitivity of the sensor50can be further tuned by changing the thickness, diameter, and/or rigidity of the membrane disc96.

The sensor data output from the vibration sensor50, which comprises data representative of the vibrations in the system, i.e., corresponding to vibratory displacement produced at the select stator bar20′, and data representative of a natural frequency of the vibration sensor50, is conveyed by the FOC58through the coupler60to the processor62. This data is monitored by the processor62in real time. The sensor data, which corresponds to a change of displacement of the membrane disc96, is used to obtain amplitude (displacement) measurements to obtain the vibration of the sensor50, as well as to obtain the natural frequency of the sensor50.

A graph illustrating a typical output spectrum of the frequencies of the vibration sensor50under normal operating conditions after the sensor data undergoes a Fast Fourier Transform (FFT) is shown inFIG. 5. The vibrations of the select stator bar20′, as measured at the membrane disc96, are depicted in the graph by the reference characters FV. FV1and FV2are harmonics of the vibrations FV. The natural frequency of the vibration sensor50is depicted in the graph by the reference characters FN. It is noted that the natural frequency of the vibration sensor50is independent of the vibrations occurring within the generator. That is, a deviation in the natural frequency FNof the sensor50typically will not affect or cause an apparent deviation in the measured vibrations FVof the select stator bar20′, and vice versa. As noted above, the majority of the vibrations sensed by the vibration sensor50comprise harmonic frequencies that are less than the natural frequency of the vibration sensor, i.e., in the specific example described above, the majority of the vibrations sensed by the vibration sensor50comprise harmonic frequencies that are less than 250 Hz, while the natural frequency of the exemplary vibration sensor may be about 410 Hz.

The processor62monitors the sensor data to look for vibrations that could result in damage to the generator components. If the monitored vibrations FVare determined to be outside of a desired amplitude or frequency range, at least one system operating parameter may be changed to alter the vibrations occurring in the generator. For example, the load of the generator may be reduced, or the temperature of a gas or water for cooling the generator may be altered.

The processor62also looks for a change in the data representative of the natural frequency FNof the vibration sensor50, as such a change may indicate structural damage, e.g., a crack, in the vibration sensor50. That is, according to the present embodiment, the peak of the natural frequency envelope of the vibration sensor50is about 410 Hz. If this value deviates from 410 Hz by a predetermined amount, such as, for example, at least about 5 Hz, the vibration sensor50may have structural damage and may be in need of being repaired or replaced. Hence, if the peak of the natural frequency of the vibration sensor50deviates from 410 Hz by at least about 5 Hz, i.e., is decreased, as shown inFIG. 6, or increased, as shown inFIG. 7, the vibration sensor50may be flagged for repair/replacement. Other factors may also be used to trigger the flagging of the vibration sensor50, such as if the frequency envelope of the natural frequency of the vibration sensor50is expanded or contracted, as depicted inFIGS. 8 and 9, respectively. It is noted that the dotted lines inFIGS. 6-9represent the frequency envelope of the vibration sensor50under normal operating conditions as depicted inFIG. 5, and are presented inFIGS. 6-9to illustrate the deviations of the frequency of the vibration sensor50in these graphs.

If the vibration sensor50is flagged, it may be removed from the select stator bar20′ and may be serviced, e.g., repaired or replaced. A new vibration sensor (or the repaired vibration sensor50) may then be placed on the select stator bar20′.

Since the condition of the vibration sensor50is monitored along with the vibrations of the select stator bar20′, any damage to the vibration sensor50can be detected at an early stage and can be performed without a physical inspection of the vibration sensor50. Further, since the data representative of the natural frequency FNof the vibration sensor50is inherently transmitted through the FOC58along with the data representative of the vibrations FVof the select stator bar20′, dedicated instruments are not required to monitor the condition of the vibration sensor50.

Referring toFIG. 10, a system200for monitoring the operating condition of an electric generator201is illustrated. The system200includes at least one vibration sensor, such as the vibration sensor50described above, and preferably comprises a plurality of vibration sensors50a-f, each vibration sensor50a-fcoupled to a corresponding stator bar as described above.

Each vibration sensor50a-fin the system200is in communication with and sends sensor data, including data representative of the vibrations received by the corresponding vibration sensor50a-fand data representative of a natural frequency of the corresponding vibration sensor50a-fas described above, to a processor202, e.g., a plant data acquisition system. Further, each vibration sensor50a-fin the system200has a unique FBG54a-fhaving a unique central Bragg wavelength λ0corresponding to the particular sensor50a-f. A source of optical radiation56, such as a broadband light source, is coupled to a plurality of FOCs58a-fextending to the vibration sensors50a-ffor providing the vibration sensors50a-fwith optical radiation. The broadband light source provides light in a range that corresponds to the reflected wavelength represented by the FBGs54a-fof the sensors50a-f. The processor202may identify the source of the data received from the sensors50a-fby the unique wavelength range reflected from each of the FBGs54a-fof the sensors50a-f.

The processor202acquires the sensor data corresponding to each of the vibration sensors50a-f. If the monitored sensor data indicates that vibrations are occurring that are outside of a predetermined range, one or more operating conditions of the generator201may be changed to alter the vibrations occurring therein. Further, if the monitored sensor data indicates that the natural frequency of any of the vibrations sensors50a-fdeviates from its normal frequency, e.g., is decreased or increased, or if the frequency envelope is expanded or contracted, that vibration sensor50may be flagged for repair/replacement, as described above.

Referring toFIGS. 11 and 12, membrane discs300,400for vibration sensors according to other embodiments of the invention are illustrated. The membrane disc300illustrated inFIG. 11comprises a generally round shape having concave rounded or contoured portions302,304,306,308removed or otherwise missing from the outer edge thereof, i.e., the portions302,304,306,308extend radially inwardly from the outer edge thereof, and the membrane disc400illustrated inFIG. 12comprises a generally round shape having larger concave hyperbolic-shaped portions402,404,406,408removed or otherwise missing from the outer edge thereof i.e., the portions402,404,406,408extend radially inwardly from the outer edge thereof. By removing the portions302-308, and402-408, the membrane discs300,400become easier to flex, which translates to a lowering of the natural frequency of the membrane discs300,400. Also, since the membrane discs300,400are easier to deflect, a smaller amplitude change in the vibration of a stator bar to which the respective vibration sensors are affixed will result in an easier flexure of the membrane disc300,400, providing a higher sensitivity to the sensor. Additionally, in the embodiment ofFIG. 12, it is believed that the hyperbolic shape that defines the portions402-408of material removed from the membrane disc400enable tuning of the membrane disc400to conform to desired design criteria. Furthermore, the hyperbolic shape of the removed portions402-408provides very low structural stress on the membrane disc400, thus reducing the possibility of crack formations in the disc400.

While the monitoring of sensor data described herein has been described in terms of using the vibration sensor50, the systems and methods of the present invention may be implemented with any sensor that provides an output that includes data representative of the natural frequency of the sensor. Further, while the conditions within an electric generator are described as being monitored herein, other types of systems can be monitored using the systems and methods described herein, i.e., the systems and methods described herein are not intended to be limited to monitoring the conditions within an electric generator.