Vibration monitoring method for component-level compressor tester

Abstract

The invention provides a vibration monitoring method for a component-level gas compressor tester, and belongs to the field of aero-engine tests. The method comprises the steps that a vibration monitoring layout scheme of the gas compressor tester is constructed; operating the compressor tester based on the vibration monitoring layout scheme of the compressor tester to carry out vibration monitoring on the compressor tester, obtaining characteristic parameters of a biaxial compressor test piece and each equipment fulcrum bearing in the compressor tester, and constructing a graded vibration monitoring frequency band, and the vibration state of the compressor tester is judged based on the obtained bearing characteristic parameters and the graded vibration monitoring frequency band. According to the method, the problems that a transmission shaft system of a component-level double-shaft compressor is long, a supporting structure is complex, and vibration monitoring and recognition are difficult under the multi-fault-mode feature are solved, and the problem that existing compressor vibration testing layout and feature recognition cannot meet multi-excitation-source and multi-fault-mode monitoring of a coaxial compressor tester is solved.

Description

Technical Field

[0001] The present application belongs to the field of aero-engine testing, and in particular relates to a vibration monitoring method for a component-level compressor tester. Background Art

[0002] Aircraft engine compressor component testing is an important means to verify the compressor design. The main characteristics of compressor component testing are high speed, long transmission shaft system, complex support structure, and multiple vibration excitation sources, which lead to extremely high risks in compressor component testing.

[0003] At present, compressor testing mainly relies on experience to arrange vibration measurement points on the installation edges of the force transmission paths of each support point of the compressor tester to monitor the operating status of the bearings of the compressor tester. However, it is impossible to establish safety monitoring of the long transmission shaft system of the component-level compressor tester supported by complex structures and under multiple fault mode characteristics. In addition, the existing online vibration monitoring method is full-band monitoring of vibration signals, which cannot accurately identify the complex vibration characteristics with multiple excitation sources and multiple fault modes online. Summary of the invention

[0004] The object of the present application is to provide a vibration monitoring method for a component-level compressor tester to solve or alleviate at least one problem in the background technology.

[0005] The technical solution of the present application is: a vibration monitoring method for a component-level compressor tester, comprising: Construct a vibration monitoring layout for a compressor tester; Based on the vibration monitoring layout scheme of the compressor tester, the compressor tester is operated to carry out vibration monitoring of the compressor tester, characteristic parameters of the biaxial compressor test piece and the support bearings of each equipment in the compressor tester are obtained, a graded vibration monitoring frequency band is constructed, and the vibration state of the compressor tester is judged based on the obtained bearing characteristic parameters and the graded vibration monitoring frequency band.

[0006] Preferably, the compressor tester includes a power system, a speed increaser, a coaxial gearbox, a torsion shaft, a dual-axis compressor test piece and an exhaust duct, wherein: The power system includes a high-pressure power system and a low-pressure power system, the speed increaser includes a first-stage speed increaser and a second-stage speed increaser, the dual-axis compressor test piece includes a low-pressure compressor and a high-pressure compressor, and the high-pressure power system and the low-pressure power system provide driving force for the high-pressure compressor and the low-pressure compressor respectively through the first-stage speed increaser and the second-stage speed increaser; The exhaust duct includes an outer exhaust duct and an inner exhaust duct. The outer exhaust duct is arranged between the low-pressure compressor and the high-pressure compressor, and the inner exhaust duct is arranged at the rear side of the high-pressure compressor.

[0007] Preferably, the vibration monitoring layout of the compressor tester is: A measuring point is set at the front support point of the low-pressure compressor, one measuring point in the horizontal direction, one measuring point in the vertical direction and one measuring point in the axial direction, to monitor the operating characteristics of the front support point bearing and the axial vibration characteristics of the shaft system of the coaxially arranged dual-axis compressor test piece; A horizontal measuring point and a vertical measuring point are set at the rear support point of the low-pressure compressor to monitor the operating characteristics of the front support point bearings of the low-pressure compressor and the high-pressure compressor; A measuring point is set at the rear support point of the high-pressure compressor, one measuring point each in the horizontal direction, the vertical direction and the axial direction, for monitoring the operating characteristics of the rear support point bearing of the high-pressure compressor and the axial vibration characteristics of the shaft system of the dual-axis compressor test piece; One measuring point is set horizontally and one vertically at the input and output positions of the torsion shaft respectively, so as to monitor the running characteristics of the front and rear fulcrum bearings of the torsion shaft; Horizontal, vertical and axial measuring points are set at the output position of the coaxial gearbox to monitor the operating status of the output end bearing of the coaxial gearbox; Arrange horizontal, vertical and axial measuring points at the input position of the coaxial gearbox to monitor the operating status of the input end bearing of the coaxial gearbox; One measuring point is set horizontally and one vertically at the input and output positions of the first-stage speed increaser, respectively, to monitor the operating characteristics of the front and rear fulcrum bearings of the first-stage speed increaser; One measuring point is set horizontally and one vertically at the input and output positions of the two-stage speed increaser, respectively, to monitor the operating characteristics of the front and rear fulcrum bearings of the two-stage speed increaser; One horizontal measuring point and one vertical measuring point are respectively set at the input and output positions of the high-pressure power system to monitor the operating characteristics of the front and rear fulcrum bearings of the high-pressure power system; One measuring point is set horizontally and one vertically at the input and output positions of the low-pressure power system respectively, so as to monitor the operating characteristics of the front and rear fulcrum bearings of the low-pressure power system; A horizontal measuring point is set at the fulcrum position of the outer duct exhaust duct to monitor the operating characteristics of the fulcrum bearing of the outer duct exhaust duct; A horizontal measuring point is set at the fulcrum position of the inner exhaust duct to monitor the operating characteristics of the fulcrum bearing of the inner exhaust duct.

[0008] Preferably, the graded vibration monitoring frequency bands include a low-frequency vibration monitoring frequency band, a medium-frequency vibration monitoring frequency band and a high-frequency vibration monitoring frequency band.

[0009] Preferably, the low-frequency vibration monitoring frequency band is a frequency band below the fundamental frequency of the biaxial compressor test piece, and the low-frequency vibration monitoring frequency band is monitored using a narrow band and vibration energy summation display method.

[0010] Preferably, the medium frequency vibration monitoring frequency band is in the range of the fundamental frequency of the biaxial compressor test piece to three times the fundamental frequency of the biaxial compressor test piece, and the medium frequency vibration monitoring frequency band is monitored using a narrowband display method.

[0011] Preferably, the high-frequency vibration monitoring frequency band is a frequency measurement range of 3 times the fundamental frequency and above of the dual-axis compressor test piece, and the high-frequency vibration monitoring frequency band is monitored using a narrow band and vibration energy summation display method.

[0012] Preferably, the process of judging the vibration state of the compressor tester based on the bearing characteristic parameters and the graded vibration monitoring frequency bands includes: Obtain the characteristic parameters of the pivot bearings of the biaxial compressor test piece and each device, and calculate the pivot bearing failure frequency; Determine the blade passing frequency according to the set speed and number of blades of the biaxial compressor test piece; Construct a hierarchical vibration monitoring frequency band analysis page for the complex vibration characteristics of each device in the compressor tester; Provide graded early warning for vibration monitoring results in graded vibration monitoring frequency bands to complete preliminary identification of potential vibration faults; The vibration monitoring results of the three graded vibration monitoring frequency bands are correlated and analyzed to achieve online fault identification and diagnosis.

[0013] The vibration monitoring method for a component-level compressor tester provided in the present application aims to solve the problems of long transmission shaft system, complex supporting structure, and difficulty in vibration monitoring and identification under multiple fault mode characteristics of a component-level dual-axis compressor. A vibration monitoring layout method is provided and graded vibration monitoring is adopted to realize graded online identification and analysis of vibration operation characteristics of complex transmission shaft system of a component-level compressor tester, solving the problem that the existing compressor vibration test layout and feature recognition cannot meet the multi-excitation source and multi-fault mode monitoring of a coaxial compressor tester. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solution provided by the present application, the following is a brief introduction to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present application.

[0015] Figure 1 This is a schematic diagram of a vibration monitoring method for a component-level compressor tester of the present application.

[0016] Figure 2 Schematic diagram of the vibration monitoring layout of the compressor tester in this application.

[0017] Figure 3 Schematic diagram of vibration analysis of a biaxial compressor test piece according to an embodiment of the present application.

[0018] Figure 4Schematic diagram of vibration analysis of a coaxial gearbox according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below in conjunction with the drawings in the embodiments of this application.

[0020] In order to overcome the problems raised in the prior art, the present application provides a vibration monitoring method for a component-level compressor tester. The method solves the problem of vibration testing with multiple excitation sources and limited measuring points for a tester with a complex supporting structure by establishing a shaft system vibration monitoring scheme for fault monitoring of an aircraft engine compressor tester. The method solves the problem of online identification of engineering-level compressor tester faults by establishing a frequency-band monitoring and identification method for compressor tester fault modes.

[0021] like Figure 1 As shown, the vibration monitoring method of the component-level compressor tester of the present application includes: Step S10, constructing a vibration monitoring layout plan for the compressor tester.

[0022] like Figure 2 The figure shows a schematic diagram of the vibration monitoring layout scheme of the compressor tester constructed in the present application, wherein the compressor tester 100 includes a power system 11, a speed increaser 12, a coaxial gearbox 13, a torsion shaft 14, a dual-axis compressor test piece 15 and an exhaust duct 16, wherein the power system 11 includes a high-pressure power system 111 and a low-pressure power system 112, the speed increaser 12 includes a first-stage speed increaser 121 and a second-stage speed increaser 122, the dual-axis compressor test piece 15 includes a low-pressure compressor 151 and a high-pressure compressor 152, and the high-pressure power system 111 and the low-pressure power system 112 provide driving force for the high-pressure compressor 152 and the low-pressure compressor 151 through the first-stage speed increaser 121 and the second-stage speed increaser 122, respectively. The exhaust duct 16 includes an outer exhaust duct 161 and an inner exhaust duct 162 . The outer exhaust duct 161 is arranged between the low-pressure compressor 151 and the high-pressure compressor 152 , and the inner exhaust duct 162 is arranged at the rear side of the high-pressure compressor 152 .

[0023] Based on the complex shaft system and failure mode of the compressor tester 100, taking the coaxial compressor tester as an example, vibration monitoring points are arranged for each system or equipment, and the layout scheme is as follows: 1) A horizontal, vertical and axial measuring point are set at the front support of the low-pressure compressor 151, for a total of three measuring points. The horizontal and vertical measuring points are used to monitor the operating characteristics of the front support bearing of the coaxially arranged dual-axis compressor test piece 15, and the axial measuring point is used to monitor the axial vibration characteristics of the shaft system of the dual-axis compressor test piece 15; 2) Two measuring points are set at the rear support point of the low-pressure compressor 151, one horizontal measuring point and one vertical measuring point, for a total of two measuring points, to monitor the operating characteristics of the front support bearings of the low-pressure compressor 151 and the high-pressure compressor 152; 3) A horizontal measuring point, a vertical measuring point and an axial measuring point are set at the rear support point of the high-pressure compressor 152, for a total of three measuring points, to monitor the operating characteristics of the rear support point bearing of the high-pressure compressor 152 and the axial vibration characteristics of the shaft system of the dual-axis compressor test piece 15; 4) Set one horizontal measuring point and one vertical measuring point at the input and output positions of the torsion shaft 14, for a total of four measuring points, to monitor the operating characteristics of the front and rear fulcrum bearings of the torsion shaft 14; 5) A three-way displacement sensor or horizontal, vertical and axial measuring points are arranged at the output position of the coaxial gearbox 13 to monitor the operating status of the output end bearing of the coaxial gearbox 13; 6) Arrange a three-way displacement sensor or arrange horizontal, vertical and axial measuring points at the input position of the coaxial gearbox 13 to monitor the operating status of the input end bearing of the coaxial gearbox 13; 7) One horizontal measuring point and one vertical measuring point are respectively set at the input and output positions of the first-stage speed increaser 121, for a total of four measuring points, to monitor the operating characteristics of the front and rear fulcrum bearings of the first-stage speed increaser 121; 8) One horizontal measuring point and one vertical measuring point are respectively set at the input and output positions of the secondary speed increaser 122, for a total of four measuring points, to monitor the operating characteristics of the front and rear fulcrum bearings of the secondary speed increaser 122; 9) One horizontal measuring point and one vertical measuring point are set at the input and output positions of the high-pressure power system 111, for a total of four measuring points, to monitor the operating characteristics of the front and rear fulcrum bearings of the high-pressure power system 111; 10) One horizontal measuring point and one vertical measuring point are respectively set at the input and output positions of the low-pressure power system 112, for a total of four measuring points, to monitor the operating characteristics of the front and rear fulcrum bearings of the low-pressure power system 111; 11) A horizontal measuring point is set at the fulcrum position of the outer duct exhaust duct 161 to monitor the operating characteristics of the fulcrum bearing of the outer duct exhaust duct 161; 12) A horizontal measuring point is set at the fulcrum position of the internal exhaust duct 162 to monitor the operating characteristics of the fulcrum bearing of the internal exhaust duct 162.

[0024] It should be noted that the vibration measuring points of the compressor tester 100 are installed on the casing mounting edge of the force transmission path of the dual-axis compressor test piece 15 or directly on the bearing seat. Except for the exhaust duct 16 (vertical state), the other systems or equipment (horizontal state) need to ensure that the vibration measuring points are arranged both horizontally and vertically in the cross section, which is used for detailed comparative analysis of the vibration characteristics of each system or equipment. In addition, the front and rear support points of the dual-axis compressor test piece 15 and the input and output ends of the coaxial gearbox 13 are provided with axial measuring points to monitor the potential risk of shaft deviation of the dual-axis compressor test piece 15 and the coaxial gearbox 13.

[0025] Based on the above measurement point arrangement, the detailed vibration characteristic measurement of the compressor tester 100 shaft system can be realized, and the shaft system operation flexibility curve can be described according to the vibration characteristics.

[0026] S20, based on the above-mentioned compressor tester vibration monitoring layout plan, operate the compressor tester to carry out vibration monitoring of the compressor tester, obtain the bearing characteristic parameters of the dual-axis compressor test piece and the support bearings of each equipment in the compressor tester, construct a graded vibration monitoring frequency band, and judge the vibration state of the compressor tester based on the obtained bearing characteristic parameters and the graded vibration monitoring frequency band.

[0027] In view of the multiple failure modes and complex vibration spectrum characteristics of component-level compressor testers, this application performs vibration monitoring and fault warning on the compressor tester based on frequency division characteristics.

[0028] In this application, the graded vibration monitoring frequency band is set to three levels, namely, low-frequency vibration monitoring frequency band, medium-frequency vibration monitoring frequency band and high-frequency vibration monitoring frequency band. The specific division method of low-frequency vibration monitoring frequency band, medium-frequency vibration monitoring frequency band and high-frequency vibration monitoring frequency band is as follows: 1) The frequency band below the fundamental frequency of the dual-axis compressor test piece is the low-frequency vibration monitoring frequency band. For the low-frequency vibration monitoring frequency band, the “narrow band and vibration energy summation” display method is used for monitoring.

[0029] 2) The range of the fundamental frequency of the biaxial compressor test piece to 3 times the fundamental frequency of the biaxial compressor test piece is used as the medium frequency vibration monitoring frequency band. For the medium frequency vibration monitoring frequency band, the “narrow band” display method is used for monitoring.

[0030] 3) The frequency measurement range from the 3 times fundamental frequency of the dual-axis compressor test piece to the analyzer is taken as the high-frequency vibration monitoring frequency band. For the high-frequency vibration monitoring frequency band, the “narrow band and vibration energy summation” display method is used for monitoring.

[0031] Tables 1 to 3 are schematic diagrams of vibration monitoring fault types and graded vibration monitoring frequency bands for a dual-axis compressor tester in an embodiment of the present application.

[0032] Table 1 Low frequency vibration fault types

[0033] Table 2 Medium frequency vibration fault types

[0034] Table 3 High frequency vibration fault types

[0035] In this application, the process of judging the vibration state of the compressor tester based on the bearing characteristic parameters and the graded vibration monitoring frequency bands includes: S21: Obtaining characteristic parameters of the pivot bearings of the biaxial compressor test piece 15 and each device, and calculating the pivot bearing failure frequency; S22: determining a blade passing frequency according to a set rotation speed and a number of blades of the biaxial compressor test piece 15; S23: Construct a hierarchical vibration monitoring frequency band analysis page for the complex vibration characteristics of each device in the compressor tester; The low-frequency vibration monitoring frequency band analysis page mainly analyzes the fundamental frequency and frequencies below the biaxial compressor test piece, and mainly analyzes the sum of narrowband frequencies and vibration energy; the medium-frequency vibration monitoring frequency band analysis page mainly analyzes the frequency spectrum characteristics between the fundamental frequency of the biaxial compressor test piece and 3 times the fundamental frequency of the biaxial compressor test piece, mainly focusing on narrowband frequency analysis; the high-frequency vibration monitoring frequency analysis page mainly analyzes the frequency spectrum characteristics above 3 times the fundamental frequency of the biaxial compressor test piece, and mainly analyzes the narrowband frequencies of the biaxial compressor test piece and the sum of vibration energy.

[0036] like Figure 3 and Figure 4 Shown is a curve showing the vibration characteristics of the dual-shaft compressor test piece and the coaxial gearbox shown in this embodiment of the present application as a function of the rotational speed.

[0037] S24: Performing graded warning on the vibration monitoring results of the graded vibration monitoring frequency bands. This embodiment only performs preliminary identification on the potential vibration faults identified in Table 1; S25: Correlation analysis is performed on the vibration monitoring results of the three graded vibration monitoring frequency bands to achieve online identification and diagnosis of the faults in the embodiment of Table 1. For the identified vibration faults, the operating status of the compressor tester can be guided by indicator lights of different colors to reduce the risk of test operation.

[0038] The vibration monitoring method for a component-level compressor tester provided in the present application aims to solve the problems of long transmission shaft system, complex supporting structure, and difficulty in vibration monitoring and identification under multiple fault mode characteristics of a component-level dual-axis compressor. A vibration monitoring layout method is provided and graded vibration monitoring is adopted to realize graded online identification and analysis of vibration operation characteristics of complex transmission shaft system of a component-level compressor tester, solving the problem that the existing compressor vibration test layout and feature recognition cannot meet the multi-excitation source and multi-fault mode monitoring of a coaxial compressor tester.

[0039] This application can provide strong support for aircraft engine ground test monitoring, troubleshooting, and future aircraft engine compressor and turbine tester construction and vibration monitoring and identification.

[0040] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A vibration monitoring method for a component-level compressor tester, characterized in that: include: Construct a vibration monitoring layout for a compressor tester; Based on the vibration monitoring layout scheme of the compressor tester, the compressor tester is operated to carry out vibration monitoring of the compressor tester, characteristic parameters of the biaxial compressor test piece and the support bearings of each equipment in the compressor tester are obtained, a graded vibration monitoring frequency band is constructed, and the vibration state of the compressor tester is judged based on the obtained bearing characteristic parameters and the graded vibration monitoring frequency band.

2. The vibration monitoring method of a component-level compressor tester according to claim 1, characterized in that: The compressor tester includes a power system, a speed increaser, a coaxial gearbox, a torsion shaft, a dual-axis compressor test piece and an exhaust duct, wherein: The power system includes a high-pressure power system and a low-pressure power system, the speed increaser includes a first-stage speed increaser and a second-stage speed increaser, the dual-axis compressor test piece includes a low-pressure compressor and a high-pressure compressor, and the high-pressure power system and the low-pressure power system provide driving force for the high-pressure compressor and the low-pressure compressor respectively through the first-stage speed increaser and the second-stage speed increaser; The exhaust duct includes an outer exhaust duct and an inner exhaust duct. The outer exhaust duct is arranged between the low-pressure compressor and the high-pressure compressor, and the inner exhaust duct is arranged at the rear side of the high-pressure compressor.

3. The vibration monitoring method of a component-level compressor tester according to claim 2, characterized in that: The vibration monitoring layout of the compressor tester is as follows: A measuring point is set at the front support point of the low-pressure compressor, one measuring point in the horizontal direction, one measuring point in the vertical direction and one measuring point in the axial direction, to monitor the operating characteristics of the front support point bearing and the axial vibration characteristics of the shaft system of the coaxially arranged dual-axis compressor test piece; A horizontal measuring point and a vertical measuring point are set at the rear support point of the low-pressure compressor to monitor the operating characteristics of the front support point bearings of the low-pressure compressor and the high-pressure compressor; A measuring point is set at the rear support point of the high-pressure compressor, one measuring point each in the horizontal direction, the vertical direction and the axial direction, to monitor the operating characteristics of the rear support point bearing of the high-pressure compressor and the axial vibration characteristics of the shaft system of the dual-axis compressor test piece; One measuring point is set horizontally and one vertically at the input and output positions of the torsion shaft respectively, so as to monitor the running characteristics of the front and rear fulcrum bearings of the torsion shaft; Horizontal, vertical and axial measuring points are set at the output position of the coaxial gearbox to monitor the operating status of the output end bearing of the coaxial gearbox; Arrange horizontal, vertical and axial measuring points at the input position of the coaxial gearbox to monitor the operating status of the input end bearing of the coaxial gearbox; One measuring point is set horizontally and one vertically at the input and output positions of the first-stage speed increaser, respectively, to monitor the operating characteristics of the front and rear fulcrum bearings of the first-stage speed increaser; One measuring point is set horizontally and one vertically at the input and output positions of the two-stage speed increaser, respectively, to monitor the operating characteristics of the front and rear fulcrum bearings of the two-stage speed increaser; One horizontal measuring point and one vertical measuring point are respectively set at the input and output positions of the high-pressure power system to monitor the operating characteristics of the front and rear fulcrum bearings of the high-pressure power system; One measuring point is set horizontally and one vertically at the input and output positions of the low-pressure power system respectively, so as to monitor the operating characteristics of the front and rear fulcrum bearings of the low-pressure power system; A horizontal measuring point is set at the fulcrum position of the outer duct exhaust duct to monitor the operating characteristics of the fulcrum bearing of the outer duct exhaust duct; A horizontal measuring point is set at the fulcrum position of the inner exhaust duct to monitor the operating characteristics of the fulcrum bearing of the inner exhaust duct.

4. The vibration monitoring method of a component-level compressor tester according to claim 3, characterized in that: The graded vibration monitoring frequency bands include a low-frequency vibration monitoring frequency band, a medium-frequency vibration monitoring frequency band and a high-frequency vibration monitoring frequency band.

5. The vibration monitoring method of a component-level compressor tester according to claim 4, characterized in that: The low-frequency vibration monitoring frequency band is a frequency band below the fundamental frequency of the dual-axis compressor test piece, and the low-frequency vibration monitoring frequency band is monitored using a narrow band and vibration energy summation display method.

6. The vibration monitoring method of a component-level compressor tester according to claim 4, characterized in that: The medium frequency vibration monitoring frequency band is in the range of the fundamental frequency of the biaxial compressor test piece to three times the fundamental frequency of the biaxial compressor test piece, and the medium frequency vibration monitoring frequency band is monitored using a narrow band display method.

7. The vibration monitoring method of a component-level compressor tester according to claim 4, characterized in that: The high-frequency vibration monitoring frequency band is a frequency measurement range of three times the fundamental frequency and above of the dual-axis compressor test piece, and the high-frequency vibration monitoring frequency band is monitored using a narrow band and vibration energy summation display method.

8. The vibration monitoring method for a component-level compressor tester according to any one of claims 5 to 7, characterized in that: The process of judging the vibration state of the compressor tester based on bearing characteristic parameters and graded vibration monitoring frequency bands includes: Obtain the characteristic parameters of the pivot bearings of the biaxial compressor test piece and each device, and calculate the pivot bearing failure frequency; Determine the blade passing frequency according to the set speed and number of blades of the biaxial compressor test piece; Construct a hierarchical vibration monitoring frequency band analysis page for the complex vibration characteristics of each device in the compressor tester; Provide graded early warning for vibration monitoring results in graded vibration monitoring frequency bands to complete preliminary identification of potential vibration faults; The vibration monitoring results of the three graded vibration monitoring frequency bands are correlated and analyzed to achieve online fault identification and diagnosis.

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