FULL-SCALE ENGINE DEMONST HAT ION OF AN ADVANCED SENSOR FAILURE DETECT ION, ISOLAI ION, 87-2259 AND ACCOMMODAllON ALGOKIlHM - PRFLIMINARY RESULTS Walter C. Merrill, John C. DeLaat, Steven M. Kroszkewicz, and Mahmood Abdelwahab National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 0 422 Abstract - The objective of the advanced detection, iso- lation, and accommodation (ADIA) program i s t o improve the overall demonstrated reliability of digital electronic control systems for turbine engines. For this purpose, algorithms have been developed which detect, isolate, and accommodate sensor failures using analytical redundancy. In this paper preliminary results of d full scale engine demonstration of the ADIA algorithm are pre- sented. Minimum detectable levels of sensor fail- ures for an FlOO turbofan engine control system are determined and compared to those obtained during a previous evaluation of this algorithm using a real- time hybrid computer simulation of the engine. Introduction The objective of the advanced detection, iso- lation, and accommodation (ADIA) program i s to improve the overall demonstrated reliability of digital electronic control systems for turbine engines by detecting, isolating, and accommodating sensor failures using analytical redundancy methods. This paper discusses the preliminary results of a full scale engine demonstration of an analytical redundancy based algorlthm developed as part of the ADIA program. Over the past 35 years hydromechanical imple- mentations of turbine engine control systems have matured into highly reliable units. However, there i s a trend towards increased engine complexity. This increased complexity i s required to meet ever increasing engine performance requirements. Conse- quently, the engine control has become increasingly complex. Because of this complexity trend and the revolution in digital electronics, the control has evolved from a hydromechanical to a full authority digital electronic (FADEC) implementation. These FADEC type controls have to demonstrate the same or improved levels of reliability as their hydro- mechanical predecessors. In an effort to improve the overall reliability of the digital electronic control system, various redundancy management techniques have been applied to both the total control system and to individual components. studies1 have shown that the least reliable of the control system components are the engine sensors. In fact some type of sensor redun- dancy will be required to achieve adequate control system reliability. One important type is analyti- cal redundancy (AR) .2 Analytical redundancy uses a model to generate redundant Informatlon that can be compared to measured information to detect fail- ures. Analytical redundancy based systems can have cost and weight savings over other approaches such as hardware redundancy. Considerable progress has been made in the application of analytical redundancy to improve turbine engine control system reliability. The Copyright (C 1981 American lnstitule of Aeronautics and Astronaulics. lnc. N o c o ~ y r i ~ h l is asserted in the Unilcd Statcs .. .. under Title 17, U.S. Code. The U.S. Government has a royalty-frcc liccnx to ercrcix all rights under the copyright claimed hcrcin for Covcrnmenlal purpous. All other rights arc revwed by ~hc copyright owner. accomplishments, surveyed i n Ref. 2, point to sev- eral technology needs. These include: (1) the ability to detect small (soft) failures, (2) real- time implementations of algorithms capable of detecting soft failures, (3) a comparison of fail- ure detection algorithm complexity versus perform- ance, (4) a full scale demonstration of a soft failure detection capability, and (5) an evaluation of the pseudolinearized modeling approach. The ADIA program conducted at the NASA Lewis Research Center addresses a l l of these technology needs. The ADIA program i s organized into four phases: development, implementation, evaluation, and demon- stration. References 3 t o 7 describe the develop- ment, implementation, and evaluation phases. In the development p h a ~ e ~ 9 ~ the ADIA algorithm was designed using advanced filtering and detection methodologies. In the Implementation phase5 this advanced algorithm was implemented i n microproces- sor based hardware. A parallel computer architec- ture (three processors) was used to allow the algorithm to execute i n a frame time consistent with stable real-time operation. In the evalu- ation phase6v7 an evaluation of algorlthm per- formance was obtained using a real-time engine simulation running on a hybrid computer. The objectives of the evaluation were to (1) validate the algorithm for sensor failure detection, isola- tion, and accommodation (DIA) effectiveness, (2) document algorithm performance, (3) validate the algorithm's real-time implementation, and (4) establish a data base for the demonstration phase of the ADIA program. This report describes the demonstration of the ADIA algorithm on a full scale FlOO engine in the NASA Lewis altitude test facility. This paper begins with a description of the test bed system used i n the demonstration of the ADIA algorithm. Next, a description of the ADIA algorithm is given followed by a description of the implementation hardware. The results of the demon- stration are then presented. Finally, conclusions and recommendations for further work are given. Test Bed System Description The algorithm was demonstrated using a test bed system consisting of (1) an engine system, (2) a multivariable control, and (3) the ADIA algorithm. The algorithm will be described i n the next section. The test bed system i s shown i n Fig. 1. Engine System The engine system consists of an FlOO turbofan engine and its associated control actuators and sensors. The FlOO turbofan engine is a high- performance, low-bypass ratio, twin-spool turbofan engine. The test engine has four controlled inputs, five sensed outputs, and four sensed envi- ronmental variables.
Transcript
FULL-SCALE ENGINE DEMONST H A T ION OF AN A D V A N C E D SENSOR FAILURE D E T E C T ION, ISOLAI ION, 87-2259 AND ACCOMMODAllON ALGOKIlHM - PRFLIMINARY RESULTS
W a l t e r C . M e r r i l l , John C . DeLaat, Steven M. Kroszkewicz , and Mahmood Abdelwahab N a t i o n a l Ae ronau t i cs and Space A d m i n i s t r a t i o n
Lewis Research Center C leve land , Ohio 44135
0 422
A b s t r a c t -
The o b j e c t i v e o f t h e advanced d e t e c t i o n , i s o - l a t i o n , and accommodation (ADIA) program i s t o improve t h e o v e r a l l demonst ra ted r e l i a b i l i t y o f d i g i t a l e l e c t r o n i c c o n t r o l systems f o r t u r b i n e eng ines. For t h i s purpose, a l g o r i t h m s have been deve loped wh ich d e t e c t , i s o l a t e , and accommodate sensor f a i l u r e s u s i n g a n a l y t i c a l redundancy. I n t h i s paper p r e l i m i n a r y r e s u l t s o f d f u l l s c a l e eng ine demons t ra t i on o f t h e ADIA a l g o r i t h m a r e p r e - sented. Minimum d e t e c t a b l e l e v e l s o f sensor f a i l - u res f o r an FlOO t u r b o f a n eng ine c o n t r o l system a r e determined and compared t o t hose o b t a i n e d d u r i n g a p r e v i o u s e v a l u a t i o n o f t h i s a l g o r i t h m u s i n g a r e a l - t i m e h y b r i d computer s i m u l a t i o n o f t h e eng ine .
I n t r o d u c t i o n
The o b j e c t i v e o f t h e advanced d e t e c t i o n , i s o - l a t i o n , and accommodation (ADIA) program i s t o improve t h e o v e r a l l demonst ra ted r e l i a b i l i t y o f d i g i t a l e l e c t r o n i c c o n t r o l systems f o r t u r b i n e eng ines by d e t e c t i n g , i s o l a t i n g , and accommodating sensor f a i l u r e s u s i n g a n a l y t i c a l redundancy methods. T h i s paper d i scusses t h e p r e l i m i n a r y r e s u l t s o f a f u l l s c a l e eng ine demons t ra t i on o f an a n a l y t i c a l redundancy based a l g o r l t h m deve loped as p a r t o f t h e A D I A program.
Over t h e p a s t 35 years hydromechan ica l i m p l e - men ta t i ons o f t u r b i n e eng ine c o n t r o l systems have matured i n t o h i g h l y r e l i a b l e u n i t s . However, t h e r e i s a t r e n d towards i nc reased eng ine c o m p l e x i t y . Th i s i nc reased c o m p l e x i t y i s r e q u i r e d t o meet ever i n c r e a s i n g eng ine per formance requ i remen ts . Conse- q u e n t l y , t h e eng ine c o n t r o l has become i n c r e a s i n g l y complex. Because o f t h i s c o m p l e x i t y t r e n d and t h e r e v o l u t i o n i n d i g i t a l e l e c t r o n i c s , t h e c o n t r o l has evo l ved f r o m a hydromechan ica l t o a f u l l a u t h o r i t y d i g i t a l e l e c t r o n i c (FADEC) imp lemen ta t i on . These FADEC t y p e c o n t r o l s have t o demonst ra te t h e same o r improved l e v e l s o f r e l i a b i l i t y as t h e i r hydro- mechan ica l p redecessors .
I n an e f f o r t t o improve t h e o v e r a l l r e l i a b i l i t y o f t h e d i g i t a l e l e c t r o n i c c o n t r o l system, v a r i o u s redundancy management t echn iques have been a p p l i e d t o b o t h t h e t o t a l c o n t r o l system and t o i n d i v i d u a l components. s t u d i e s 1 have shown t h a t t h e l e a s t r e l i a b l e o f t h e c o n t r o l system components a r e t h e eng ine sensors . I n f a c t some t y p e o f sensor redun- dancy w i l l be r e q u i r e d t o ach ieve adequate c o n t r o l system r e l i a b i l i t y . One i m p o r t a n t t y p e i s a n a l y t i - c a l redundancy (AR) . 2 A n a l y t i c a l redundancy uses a model t o gene ra te redundant I n f o r m a t l o n t h a t can be compared t o measured i n f o r m a t i o n t o d e t e c t f a i l - u res . A n a l y t i c a l redundancy based systems can have c o s t and w e i g h t sav ings over o t h e r approaches such as hardware redundancy.
Cons ide rab le p rog ress has been made i n t h e a p p l i c a t i o n o f a n a l y t i c a l redundancy t o improve t u r b i n e eng ine c o n t r o l system r e l i a b i l i t y . The
Copyright (C 1981 American lnstitule of Aeronautics and Astronaulics. lnc. No c o ~ y r i ~ h l is asserted in the Unilcd Statcs . . ..
under Title 17, U.S. Code. The U.S. Government has a royalty-frcc liccnx to ercrcix all rights under the copyright
claimed hcrcin for Covcrnmenlal purpous. All other rights arc revwed by ~ h c copyright owner.
accompl ishments , surveyed i n Ref . 2, p o i n t t o sev- e r a l t echno logy needs. These i n c l u d e : ( 1 ) t h e a b i l i t y t o d e t e c t sma l l ( s o f t ) f a i l u r e s , ( 2 ) r e a l - t i m e imp lemen ta t i ons o f a l g o r i t h m s capab le o f d e t e c t i n g s o f t f a i l u r e s , ( 3 ) a compar ison o f f a i l - u r e d e t e c t i o n a l g o r i t h m c o m p l e x i t y versus pe r fo rm- ance, ( 4 ) a f u l l s c a l e demons t ra t i on o f a s o f t f a i l u r e d e t e c t i o n c a p a b i l i t y , and ( 5 ) an e v a l u a t i o n o f t h e p s e u d o l i n e a r i z e d mode l i ng approach. The ADIA program conducted a t t h e NASA Lewis Research Center addresses a l l o f t hese techno logy needs.
The ADIA program i s o rgan i zed i n t o f o u r phases: development, imp lemen ta t i on , e v a l u a t i o n , and demon- s t r a t i o n . References 3 t o 7 d e s c r i b e t h e deve lop- ment, imp lemen ta t i on , and e v a l u a t i o n phases. I n t h e development p h a ~ e ~ 9 ~ t h e A D I A a l g o r i t h m was des igned u s i n g advanced f i l t e r i n g and d e t e c t i o n me thodo log ies . I n t h e Imp lemen ta t i on phase5 t h i s advanced a l g o r i t h m was implemented i n m ic rop roces - so r based hardware. A p a r a l l e l computer a r c h i t e c - t u r e ( t h r e e p rocesso rs ) was used t o a l l o w t h e a l g o r i t h m t o execu te i n a f rame t i m e c o n s i s t e n t w i t h s t a b l e r e a l - t i m e o p e r a t i o n . I n t h e e v a l u - a t i o n phase6v7 an e v a l u a t i o n o f a l g o r l t h m p e r - formance was o b t a i n e d u s i n g a r e a l - t i m e eng ine s i m u l a t i o n r u n n i n g on a h y b r i d computer. The o b j e c t i v e s o f t h e e v a l u a t i o n were t o ( 1 ) v a l i d a t e t h e a l g o r i t h m f o r sensor f a i l u r e d e t e c t i o n , i s o l a - t i o n , and accommodation (D IA ) e f f e c t i v e n e s s , ( 2 ) document a l g o r i t h m per formance, ( 3 ) v a l i d a t e t h e a l g o r i t h m ' s r e a l - t i m e imp lemen ta t i on , and ( 4 ) e s t a b l i s h a d a t a base f o r t h e demons t ra t i on phase o f t h e ADIA program. T h i s r e p o r t d e s c r i b e s t h e demons t ra t i on o f t h e ADIA a l g o r i t h m on a f u l l s c a l e FlOO eng ine i n t h e NASA Lewis a l t i t u d e t e s t f a c i l i t y .
Th i s paper beg ins w i t h a d e s c r i p t i o n o f t h e t e s t bed system used i n t h e demons t ra t i on o f t h e ADIA a l g o r i t h m . Next , a d e s c r i p t i o n o f t h e ADIA a l g o r i t h m i s g i v e n f o l l o w e d by a d e s c r i p t i o n o f t h e imp lemen ta t i on hardware. The r e s u l t s o f t h e demon- s t r a t i o n a r e t h e n p resen ted . F i n a l l y , conc lus ions and recommendations f o r f u r t h e r work a r e g i v e n .
Tes t Bed System D e s c r i p t i o n
The a l g o r i t h m was demonst ra ted u s i n g a t e s t bed system c o n s i s t i n g o f ( 1 ) an eng ine system, ( 2 ) a m u l t i v a r i a b l e c o n t r o l , and ( 3 ) t h e ADIA a l g o r i t h m . The a l g o r i t h m w i l l be d e s c r i b e d i n t h e n e x t s e c t i o n . The t e s t bed system i s shown i n F i g . 1 .
Eng ine System
The eng ine system c o n s i s t s o f an FlOO t u r b o f a n eng ine and i t s a s s o c i a t e d c o n t r o l a c t u a t o r s and sensors . The FlOO t u r b o f a n eng ine i s a h i g h - per formance, low-bypass r a t i o , t w i n - s p o o l t u r b o f a n eng ine . The t e s t eng ine has f o u r c o n t r o l l e d i n p u t s , f i v e sensed o u t p u t s , and f o u r sensed e n v i - ronmenta l v a r i a b l e s .
These v a r i a b l e s a r e d e f i n e d as f o l l o w s .
C o n t r o l l e d eng ine i n p u t s , Ucom and Um
WF Main combustor f u e l f l o w A F Exhaust n o z z l e a rea C I V V Fan I n l e t v a r i a b l e vanes R C V V Rear compressor v a r i a b l e vanes
Sensed eng ine o u t p u t s . Zm
N1 Fan speed N2 Compressor speed PT4 Burner p r e s s u r e PT6 Exhaust n o z z l e p r e s s u r e F T I l Fan t u r b i n e i n l e t t empera tu re
Sensed env i ronmen ta l v a r i a b l e s , Em
PO Ambient ( s t a t i c ) p r e s s u r e PT2 Fan i n l e t ( t o t a l ) p r e s s u r e TT2 Fan i n l e t t empera tu re TT25 Compressor i n l e t t empera tu re
S t r i c t l y speaking, TT25 i s a sensed eng ine o u t p u t v a r i a b l e . However, s i n c e TT25 i s used o n l y as a s c h e d u l i n g v a r i a b l e i n t h e c o n t r o l ( l i k e TT2), i t i s cons ide red an env i ronmen ta l v a r i a b l e and i s n o t covered by t h e ADIA l o g i c .
M u l t i v a r i a b l e C o n t r o l System
The m u l t i v a r i a b l e c o n t r o l (MVC) system shown i n F i g . 1 i s e s s e n t i a l l y a model f o l l o w i n g , p r o p o r - t i o n a l - p l u s - i n t e g r a l c o n t r o l . The M V C c o n t r o l 8 was p r e v i o u s l y demonst ra ted i n an a l t i t u d e t e s t o f an F l O O eng ine.9 The components o f t h e c o n t r o l a r e t h e r e f e r e n c e p o i n t schedu les , t h e t r a n s i t i o n schedu les , t h e p r o p o r t i o n a l c o n t r o l l o g i c , t h e i n t e g r a l c o n t r o l l o g i c , and t h e eng ine p r o t e c t i o n l o g i c . The r e f e r e n c e p o i n t schedules gene ra te a d e s i r e d eng ine o p e r a t i n g p o i n t i n response t o t h e p i l o t ' s t h r u s t command (PLA) and sensed eng ine env i ronment . The t r a n s i t i o n l o g i c genera tes r a t e l i m i t e d command t r a j e c t o r i e s f o r smooth t r a n s i t i o n between s t e a d y - s t a t e o p e r a t i n g p o i n t s . The p r o p o r - t i o n a l and i n t e g r a l c o n t r o l l o g i c m i n i m i z e t r a n s i - e n t and s t e a d y - s t a t e d e v i a t i o n s f r o m t h e commanded t r a j e c t o r i e s . The eng ine p r o t e c t i o n l o g i c l i m i t s t h e s i z e o f t h e commanded eng ine i n p u t s . The n o r - mal c o n t r o l mode i n t h e MVC l o g i c used f u e l f l o w t o s e t eng ine f a n speed and n o z z l e a rea t o s e t n o z z l e p r e s s u r e ( e n g i n e p r e s s u r e r a t i o ) . However, a t t hose c o n d i t i o n s where l i m i t i n g i s r e q u i r e d , f u e l f l o w can be used t o l i m i t t h e maximum FTIT, t h e maximum PT4, o r t h e minimum PT4.
Demonst ra t ion Hardware --
The ADIA a l g o r i t h m was demonst ra ted u s i n g an F l O O eng ine i n t h e NASA Lewis a l t i t u d e t e s t f a c i l - i t y . T h i s f a c i l i t y can d u p l i c a t e a w ide range o f f l i g h t c o n d i t i o n s ( a l t l t u d e and Mach number). Reference 10 d e s c r i b e s t h e m ic rop rocesso r -based c o n t r o l system computer wh ich implemented t h e MVC and ADIA a l g o r i t h m s , i n c l u d i n g accompanying i n t e r - f ace and m o n i t o r i n g hardware i n t e r a c t i v e d a t a a c q u i s i t i o n s o f t w a r e . A sepa ra te persona l -computer - based system f o r s i m u l a t i n g sensor f a i l u r e s l 1 was used. T h i s f a i l u r e s i m u l a t o r was l o c a t e d between t h e eng ine sensors and t h e c o n t r o l system computer. I t s i m u l a t e d sensor f a i l u r e s by add ing an a p p r o p r i - a t e b i a s v o l t a g e t o t h e s e l e c t e d eng ine sensor
o u t p u t s s i g n a l s . A l l sensor f a i l u r e s ( i . e . , b o t h ha rd and s o f t ) were i n j e c t e d i n t h i s f a s h i o n .
A l g o r i t h m D e s c r i p t i o n
The ADIA a l g o r i t h m d e t e c t s , i s o l a t e s , and accommodates sensor f a i l u r e s i n an F l O O t u r b o f a n eng ine c o n t r o l system. The a l g o r i t h m i n c o r p o r a t e s advanced f i l t e r i n g and d e t e c t i o n l o g i c and i s gene ra l enough t o be a p p l i e d t o d i f f e r e n t eng ines o r o t h e r t ypes o f c o n t r o l systems. The ADIA a l g o r i t h m ( F i g . 1 ) c o n s i s t s o f t h r e e e l e r n ~ n t s : ( 1 ) ha rd sensor f a i l u r e d e t e c t i o n and i s o l a t i o n l o g i c . ( 2 ) s o f t sensor f a i l u r e d e t e c t i o n and i s o l a - t i o n l o g i c , and ( 3 ) an accommodation f i l t e r . Hard f a i l u r e s a r e d e f i n e d as o u t - o f - r a n g e o r l a r g e b i a s e r r o r s t h a t occu r i n s t a n t a n e o u s l y i n t h e sensed va lues . S o f t f a i l u r e s a r e d e f i n e d as sma l l b i a s e r r o r s o r d r i f t e r r o r s t h a t i n c r e a s e r e l a t i v e l y s l o w l y w i t h t i m e .
I n t h e normal o r u n f a i l e d mode o f o p e r a t i o n , t h e accommodation f i l t e r uses t h e f u l l s e t o f eng ine measurements t o gene ra te a s e t o f o p t i m i l e s t i m a t e s o f t h e measurements. These es t ima tes ( Z ) a r e used by t h e c o n t r o l law. When a sensor f a i l u r e occu rs , t h e d e t e c t i o n l o g i c determines t h a t a f a i l u r e has occu r red . The i s o l a t i o n l o g i c t h e n determines wh ich sensor i s f a u l t y . T h i s s t r u c t u r a l i n f o r m a t i o n i s passed t o t h e accommodation f i l t e r . The accommoda t i o n f i l t e r removes t h e f a u l t y measurement f r o m f u r t h e r c o n s i d e r a t i o n . The f i l t e r , however, c o n - t i n u e s t o gene ra te t h e f u l l s e t o f o p t i m a l e s t i m a t e s f o r t h e c o n t r o l . Thus t h e c o n t r o l does n o t have t o r e s t r u c t u r e f o r any sensor f a i l u r e . The A D I A a l g o r i t h m i n p u t s as shown i n F i g . 1 a r e t h e sensed eng ine o u t p u t v a r i a b l e s , Zm, and t h e sensed eng ine i n p u t v a r i a b l e s , The o u t p u t s o f t h e a l g o - r i t h m , t h e e s t i m a t 2 1 t h i t ) . o f t h e measured eng ine o u t p u t s , Z m ( t ) , a r e used as i n p u t t o t h e p r o p o r - t i o n a l p a r t o f t h e c o n t r o l . D u r i n g normal mode o p e r a t i o n , eng ine measurements a r e used i n t h e i n t e g r a l c o n t r o l t o ensure a c c u r a t e s t e a d y - s t a t e o p e r a t i o n . When a sensor f a i l u r e i s accommodated, t h e measurement i n t h e i n t e g r a l c o n t r o l i s r ep laced w i t h t h e co r respond ing accommodation f i l t e r e s t i - mate by r e c o n f i g u r i n g t h e i n t e r f a c e s w i t c h m a t r i x .
Accommodation F i l t e r
The accommodation f i l t e r model a l o n g w i t h a Kaltnan g a i n es t ima tes -o f t h e eng ine s t a t e s o u t p u t s Z as f o l l o w s .
nco rpo ra tes an eng ine u ~ d a t e t o gene ra te
X and t h e eng ine
Here t h e s u b s c r i p t b r e p r e s e n t s t h e base p o i n t ( s t e a d y - s t a t e eng ine o p e r a t i n g p o i n t ) and X i s t h e 4 by 1 model s t a t e v e c t o r , Um t h e 4 by 1 sensed c o n t r o l v e c t o r , and 2, i s t h e 5 by 1 sensed o u t p u t v e c t o r . The m a t r i x K i s t h e Kalman g a i n m a t r i x and y i s t h e r e s i d u a l v e c t o r . The F , G, H, and D m a t r i c e s a r e t h e a p p r o p r i a t e l y dimensioned system m a t r i c e s . T h e i r i n d i v i d u a l m a t r i x elements a l o n g w i t h t hose o f K a r e c o r - r e c t e d by t h e eng ine i n l e t c o n d i t i o n s - Em and scheduled an n o n l i n e a r f u n c t i o n s o f Z . These f u n c t i o n s a r e g i v e n i n Ref. 2.
R e c o n f i g u r a t i o n o f t h e accommodation f i l t e r , a f t e r t h e d e t e c t i o n and i s o l a t i o n o f a sensor f a i l - u re , i s accompl ished by f o r c i n g t h e a p p r o p r i a t e r e s i d u a l e lement t o ze ro . Th i s e f f e c t i v e l y s u b s t i - t u t e s t h e e s t i m a t e f o r t h e feedback (sensed) v a r i - a b l e . For example i f a compressor speed sensor f a i l u r e (N2) has been i s o l a t e d , t h e e f f e c t o f r econ - f i g u r a t i o n i s t o f o r c e y2 = 0. T h i s i s e q u i v a l e n t t o s e t t i n g sensed N2 equal t o t h e e s t i m a t e o f N2 genera ted by t h e f i l t e r . The r e s i d u a l s gen- e r a t e d by t h e accommodation f i l t e r a r e used i n t h e ha rd f a i l u r e d e t e c t i o n l o g i c .
Ha&Failure De&c_tion and I s o l a t i o n Log i c
The hard sensor f a i l u r e d e t e c t i o n and i s o l a - t i o n l o g i c i s s t r a i g h t f o r w a r d . To accompl ish ha rd f a i l u r e d e t e c t i o n and i s o l a t i o n t h e a b s o l u t e va lue o f each component o f t h e r e s i d u a l v e c t o r i s com- pared t o i t s own t h r e s h o l d . I f t h e r e s i d u a l abso l u t e va lue i s g r e a t e r t han t h e t h r e s h o l d , then a f a i l u r e i s d e t e c t e d and i s o l a t e d f o r t h e sensor co r respond ing t o t h e r e s i d u a l e lement . Th resho ld s i z e s a r e i n i t i a l l y de termined f rom t h e s tanda rd d e v i a t i o n o f t h e n o i s e on t h e sensors . These s tanda rd d e v i a t i o n magnitudes a r e then i nc reased t o account f o r mode l i ng e r r o r s i n t h e accommodation f i l t e r . The ha rd d e t e c t i o n t h r e s h o l d va lues a r e t w i c e t h e magni tude o f t hese a d j u s t e d s tanda rd d e v i a t i o n s . These magnitudes a r e summarized I n 'Table 1 .
S o f t F a i l u r e D e t e c t i o n and I s o l a t i o n Log ic -
The s o f t f a i l u r e d e t e c t i o n l o g i c c o n s i s t s o f m u l t i p l e - h y p o t h e s i s - b a s e d t e s t i n g . Each hypo thes i s i s implemented u s i n g a Kalman f i l t e r . The s o f t f a i l u r e d e t e c t i o n / i s o l a t i o n l o g i c s t r u c t u r e i s shown i n F i g . 2. A t o t a l o f s i x hypo thes i s f i l t e r s a r e shown, one f o r normal mode o p e r a t i o n and f i v e f o r t h e f a i l u r e modes (one f o r each eng ine o u t p u t senso r ) . The s t r u c t u r e f o r each hypo thes i s f i l t e r i s i d e n t i c a l t o t h e accommodation f i l t e r . However, each hypo thes i s f i l t e r uses a d i f f e r e n t s e t o f measurements. For example t h e f i r s t hypo thes i s f i l t e r (HI) uses a l l o f t h e sensed eng ine o u t p u t s excep t t h e f i r s t , N1. The second uses a l l o f t h e sensed o u t p u t s excep t t h e second, N2, and so on. Thus, each hypo thes i s f i l t e r genera tes a un ique r e s i d u a l v e c t o r , y i . From t h i s r e s i d u a l each h y p o t h e s i s f i l t e r genera tes a s t a t i s t i c o r l i k e l i - hood based upon a we ighted sum o f squared r e s i d u a l s (WSSR). Assuming Gaussian sensor n o i s e , each sam- p l e o f y i has a c e r t a i n l i k e l i h o o d o r p r o b a b i l i t y .
where k i s a c o n s t a n t and
WSSR 1 = y;Z-'yi
The 61 a r e t h e s tanda rd d e v i a t i o n s d e f i n e d i n Tab le 1 . These s tanda rd d e v i a t i o n va lues s c a l e t h e r e s i d u a l s t o u n i t l e s s q u a n t i t i e s t h a t can be summed t o f o r m WSSR. The WSSR s t a t i s t i c i s smoothed t o remove g ross n o i s e e f f e c t s by a f i r s t o r d e r l a g
w i t h a t i m e c o n s t a n t o f 0.1 sec. M a t h e m a t i c a l l y , when t h e l o g o f t h e r a t i o o f l i k e l i h o o d s i s taken, t hen
The l o g o f t h e r a t i o o f each h y p o t h e s i s l i k e l i h o o d t o t h e normal mode l i k e l i h o o d i s c a l c u l a t e d . I f t h e maximum l o g l i k e l i h o o d r a t i o exceeds t h e t h r e s - h o l d , t hen a f a i l u r e i s d e t e c t e d and i s o l a t e d and accommodation occu rs . I f a sensor f a i l u r e has occu r red I n N1 f o r example, a l l o f t h e h y p o t h e s i s f i l t e r s excep t H1 w i l l be c o r r u p t e d by t h e f a u l t y i n f o r m a t i o n . Thus each o f t h e co r respond ing l i k e - l i h o o d s w i l l be sma l l excep t f o r HI. Thus, LR1 w i l l be t h e maximum and i t w i l l be compared t o t h e t h r e s h o l d t o d e t e c t t h e f a i l u r e .
I n i t i a l l y , t h e s o f t f a i l u r e d e t e c t i o n / i s o l a t i o n t h r e s h o l d was determined by s tanda rd s t a t i s t i c a l a n a l y s i s o f t h e r e s i d u a l s t o s e t t h e con f i dence l e v e l o f f a l s e a larms and missed d e t e c t i o n s . Next , t h e t h r e s h o l d was m o d i f i e d t o account f o r mode l i ng e r r o r . I t was soon appa ren t f r o m i n i t i a l e v a l u a t i o n s t u d i e s t h a t t r a n s i e n t mode l i ng e r r o r was dominant i n d e t e r m i n i n g t h e f i x e d t h r e s h o l d l e v e l s . I t was a l s o c l e a r t h a t t h i s t h r e s h o l d was t o o l a r g e f o r d e s i r a b l e s t e a d y - s t a t e o p e r a t i o n . Thus, an a d a p t i v e t h r e s h o l d was i n c o r p o r a t e d . The a d a p t i v e t h r e s h o l d i s t r i g g e r e d by an i n t e r n a l c o n t r o l system v a r i a b l e wh ich i s I n d i c a t i v e o f t r a n s i e n t o p e r a t i o n . When t h e eng ine expe r i ences a t r a n s i e n t , t h e i s o l a t i o n t h r e s h o l d i s expanded. The e x a c t m o d i f i c a t i o n was found by e x p e r i m e n t a t i o n on a s i m u l a t i o n t o m i n i m i z e f a l s e a larms d u r i n g t r a n s i e n t s . The a d a p t i v e t h r e s - h o l d expans ion l o g i c enab led t h e s t e a d y - s t a t e de tec - t i o n t h r e s h o l d t o be reduced t o 80 p e r c e n t o f i t s o r i g i n a l va lue . A d d i t i o n a l d e t a i l s o f t h e a l g o r i t h m can be found i n Re f . 6.
F a i l u r e Accommodation
For accommodation two sepa ra te s teps a r e t aken . F i r s t , a l l seven o f t h e f i l t e r s ( t h e accommodation f i l t e r and t h e s i x h y p o t h e s i s f i l t e r s ) a r e recon- f i g u r e d t o account f o r t h e d e t e c t e d f a i l u r e mode. Second, i f a s o f t f a i l u r e was d e t e c t e d , t h e s t a t e s and e s t i m a t e s o f a l l seven f i l t e r s a r e updated t o t h e c o r r e c t va lues o f t h e h y p o t h e s i s f i l t e r wh ich cor responds t o t h e f a i l e d sensor .
AOIA A l g o r i t h m I m p l e m e n t a t l o n
To conduct t h e t e s t - b e d demons t ra t i on an imp lemen ta t i on o f t h e ADIA a l g o r i t h m was I n t e g r a t e d w i t h an e x i s t i n g microcomputer imp lemen ta t i on o f t h e F l O O m u l t i v a r i a b l e c o n t r o l (MVC) a l g o r i t h m . The r e s u l t i n g c o n t r o l s microcomputer system was based on t h e I n t e l 80186 m ic rop rocesso r a r c h i t e c - t u r e . To s a t i s f y t h e c o n t r o l update i n t e r v a l r equ i remen t o f 40 msec t o guarantee eng ine s t a b i l - i t y , t h r e e p rocesso rs (CPU1s) o p e r a t i n g i n p a r a l l e l a r e used. Data i s t r a n s f e r r e d between CPU's t h rough d u a l - p o r t e d memory. S y n c h r o n i z a t i o n between CPU's I s ach ieved th rough i n t e r r u p t s .
The e x i s t i n g MVC imp lemen ta t i on was programmed i n f i x e d p o i n t assembly language and was used w l t h - o u t change on CPU No. 1 . The ADIA a l g o r i t h m exe- cu tes on CPU1s No. 2 and No. 3 and was programmed u s i n g f l o a t i n g p o i n t a r i t h m e t i c and FORTRAN. The
t o t a l memory requ i remen t f o r t h e t h r e e CPU's i s 51 Kbytes f o r t h e a l g o r i t h m and 15 Kbytes f o r t h e e x e c u t i v e . I n a l l cases t h e code and c o n s t a n t s were about 65 p e r c e n t and t h e d a t a o r v a r i a b l e s about 35 p e r c e n t o f t h e t o t a l memory r e q u i r e d . A d d i t i o n a l d e t a i l s o f t h e imp lemen ta t i on can be found i n Re f . 6 .
Demonst ra t ion R e s u l t s -. -. - - -. . --
T h i s s e c t i o n d e s c r i b e s p r e l i m i n a r y r e s u l t s o b t a i n e d i n demons t ra t i ng t h e ADIA a l g o r i t h m u s i n g t h e F l O O eng ine. The t e s t p rocedu re and t h e r e s u l t s o f t h e demons t ra t i on a r e d i scussed . The o b j e c t i v e o f t h e eng ine t e s t was t o demonst ra te t h e o p e r a t i o n and per formance o f t h e A D I A a l g o r i t h m and i t s imp lemen ta t i on over a s u b s t a n t i a l p o r t i o n o f t h e f l i g h t enve lope o f t h e F l O O eng ine.
Procedure -
l h e t e s t m a t r i x , shown i n F i g . 3, summarizes t h e t e s t s used t o demonst ra te t h e a l g o r i t h m . The d i f f e r e n t eng ine o p e r a t i n g c o n d i t i o n s ( a l t i t u d e / M a c h number) used f o r t h e demons t ra t i on a r e l i s t e d ac ross t h e t o p o f t h e m a t r i x and t h e d i f f e r e n t t e s t s con- ducted a t t hese p o i n t s a l o n g t h e s i d e . C u r r e n t l y , o n l y r e s u l t s f o r t h e 10 000 f t a l t i t u d e , 0.6 Mach number ( 1 0 K/D.6) o p e r a t i n g c o n d i t i o n have been o b t a i n e d . Eng ine power (PLA) s e t t i n g s were s e l e c t e d which r e p r e s e n t maximum n o n a f t e r b u r n i n g ( i n t e r m e d i - a t e ) t h r u s t (PLA = 80) and -50 p e r c e n t o f i n t e r m e - d i a t e t h r u s t (PLA = 50 and 70 ) . The r a t i o n a l e used t o s e l e c t t h e t e s t m a t r i x o p e r a t i n g p o i n t s was t o d u p l i c a t e as many o f t h e p o i n t s used i n t h e F l O O M u l t i v a r i a b l e C o n t r o l program7 as p o s s i b l e , t o a v o i d h i g h f a n i n l e t p ressu res , and t o reasonab l y span t h e enve lope. T h i s r a t i o n a l e i s a compromise among t a k i n g advantage o f p r e v i o u s r e s u l t s f o r com- p a r i s o n , l i m i t e d r i s k eng ine o p e r a t i o n , and f u l l enve lope v a l i d a t i o n .
The t y p e o f t e s t s used i n t h e demons t ra t i on were s e l e c t e d t o c o m p l e t e l y d e f i n e d e t e c t i o n pe r formance f o r t h r e e common f a i l u r e modes. A l so , t e s t s were conducted t o de te rm ine eng ine c o n t r o l per formance w i t h and w i t h o u t eng ine sensor f a i l - u r e s . The t e s t s a r e summarized i n Tab le 2 .
R e s u l t s
Three t ypes o f demons t ra t i on r e s u l t s w i l l now be p resen ted . The f i r s t shows t h e accuracy o f t h e accommodation f i l t e r w i t h no sensor f a i l u r e s . t h e second shows t h e d e t e c t i o n per formance o f t h e ADIA a l g o r i t h m . F i n a l l y , accommodation per formance i s demonst ra ted.
E s t i m a t o r accu racy . The s i n g l e most i m p o r t a n t element i n d e t e r m i n i n g ADIA a l g o r i t h m per formance i s t h e accuracy o f t h e eng ine o u t p u t e s t i m a t e s used i n t h e a l g o r i t h m . These e s t i m a t e s a r e determined u s i n g t h e accommodation f i l t e r , wh i ch incorporates a s i m p l i f i e d eng ine model. A sample o f t h e accuracy o f t h e f i l t e r i s p resen ted i n F i g . 4 wh ich shows an I d l e - t o - i n t e r m e d i a t e - p o w e r PLA p u l s e t r a n s i e n t gen- e r a t e d a t t h e 10 K/0.6 c o n d i t i o n . The v a r i a b l e s shown, f a n speed ( N l ) and exhaust n o z z l e p r e s s u r e (PT6) , demonst ra te t h e e x c e l l e n t e s t i m a t e accuracy ach ieved . These r e s u l t s a r e t y p i c a l o f t h e o t h e r e s t i m a t e s .
Detec t ion /accommodat ion -. . - - - - -- . . - - per formance. - -. -- l w o types o f sensor f a i l u r e were cons ide red , ha rd and s o f t . Hard f a i l u r e s , because o f t h e i r s i z e , a r e e a s i l y d e t e c t e d . Thus, ha rd f a i l u r e d e t e c t i o n per formance, a l t h o u g h i m p o r t a n t t o system r e l i a b i l i t y , was exam- i n e d a t o n l y one o p e r a t i n g c o n d i t i o n ( 1 0 K/0 .6) . The ADIA a l g o r i t h m exhibited e x c e l l e n t h a r d d e t e c - t i o n per formance a t t h i s c o n d i t i o n . There were no f a l s e a larms o r missed d e t e c t i o n s o f any ha rd f a i l u r e s . Hard f a i l u r e s were i n j e c t e d i n each o f t h e eng ine sensor o u t p u t s i g n a l s . Success fu l d e t e c - t i o n and accommodation o f t h e f a i l u r e was accom- p l i s h e d i n each case. I n a d d i t i o n no f a l s e a larms i n t h e ha rd d e t e c t i o n l o g i c were encountered d u r i n g t h e subsequent s o f t f a i l u r e demons t ra t i on .
S o f t sensor f a i l u r e s , a l t h o u g h sma l l i n magni- t ude , i f unde tec ted may r e s u l t i n degraded o r unsafe eng ine o p e r a t i o n . S o f t f a i l u r e s a r e more d i f f i c u l t t o d e t e c t t hen ha rd f a i l u r e s . T h e r e f o r e t h e demon- s t r a t i o n c o n c e n t r a t e d on s o f t f a i l u r e per formance. Two s o f t f a i l u r e modes were s t u d i e d , b i a s and d r i f t . The c r i t e r i a used t o e v a l u a t e d e t e c t i o n , i s o l a t i o n , and accommodation per formance were: ( 1 ) minimum d e t e c t a b l e b i a s va lues and d r i f t r a t e s , ( 2 ) e lapsed t i m e between sensor f a i l u r e and d e t e c t i o n , ( 3 ) s t e a d y - s t a t e per formance d e g r a d a t i o n a f t e r f a i l u r e accommodation, and ( 4 ) t r a n s i e n t response o f t h e eng ine t o t h e f i l t e r and c o n t r o l r e c o n f i g u - r a t i o n o f f a i l u r e accommodation. The minimum d e t e c t a b l e l e v e l s o f b i a s and d r i f t r a t e o b t a i n e d f o r t h e 10 K/0.6 c o n d i t i o n a r e summarized i n Tab le 3. The minimum d e t e c t a b l e d r i f t r a t e s were determined by a d j u s t i n g t h e d r i f t magni tude such t h a t a f a i l u r e was d e t e c t e d -5 sec a f t e r f a i l u r e i n c e p t i o n .
The demons t ra t i on r e s u l t s a r e compared t o t h e l e v e l s o b t a i n e d d u r i n g t h e r e a l - t i m e h y b r i d e v a l u - a t i o n phase o f t h e program. The comparison a t PLA = 80' shows an e x c e l l e n t agreement f o r b o t h b i a s and d r i f t magni tudes. A t PLA = 50" however, t h e demons t ra t i on r e s u l t s a r e s l i g h t l y h i g h e r t h a n t h e h y b r i d e v a l u a t i o n r e s u l t s . I n t h i s case t h e d e t e c t i o n t h r e s h o l d has been expanded by a f a c t o r o f two t o s tudy t h e d e g r a d a t i o n i n per formance t h l s would cause. I n gene ra l , t h e d e t e c t i o n l e v e l s a r e s t i l l good excep t f o r N1. The a l g o r i t h m was unab le t o d e t e c t a f a i l u r e s m a l l e r t h a n t h e h a r d d e t e c t i o n l e v e l o f 600 rpm.
A d d i t i o n a l l y , d e t e c t i o n per formance f o r sequen- t i a l f a i l u r e s was s t u d i e d . S i x d i f f e r e n t sequences o f s o f t f a i l u r e s were i n j e c t e d i n t o t h e t e s t bed system. One example o f a f a i l u r e sequence was t o f a i l N1, t h e n 4 sec l a t e r f a l l N2, t h e n PT4, and t h e n PT6. I n each case t h e a l g o r i t h m s u c c e s s f u l l y d e t e c t e d and accommodated each sensor f a i l u r e i n t h e c o r r e c t o r d e r . These t e s t s demonst ra te t h e a b i l i t y o f t h e a l g o r i t h m t o c o n t i n u e t o s u c c e s s f u l l y p e r f o r m even a f t e r some sensors have f a i l e d .
F i n a l l y , a s imu l taneous s o f t f a i l u r e o f PT4 and PT6 ( b o t h f a i l e d a t t h e same i n s t a n t o f t i m e ) was i n j e c t e d i n t o t h e eng ine system. The a l g o - r i t h m , a l t h o u g h n o t s p e c i f i c a l l y des igned f o r t h l s ex t reme ly l ow p r o b a b i l i t y even t , s u c c e s s f u l l y d e t e c t e d and accommodated t h l s f a i l u r e s c e n a r i o .
Accommodation per formance. Two exper iments were used t o demonst ra te t h e success fu l accommodation o f
sensor f a i l u r e s . The f i r s t exper iment c o n s i s t e d o f i n j e c t i n g , d e t e c t i n g , and accommodating a s i n g l e sensor f a i l u r e and then commanding a PLA p u l s e t r a n s i e n t . Engine per formance w i t h t h i s accommo dated f a i l e d sensor i s compared t o normal mode eng ine per formance. T y p i c a l r e s u l t s a r e shown f o r t h e PT6 s i n g l e f a i l u r e case f o r f a n speed ( F i g . 5 ( a ) ) and exhaust n o z z l e p r e s s u r e ( F i g . 5 ( b ) ) . Performance was good s i n c e t h e d e s i r e d o r reques t va lues were c l o s e l y m a i n t a i n e d . A s l i g h t d r o p i n a c t u a l P l 6 can be seen b u t t h i s i s a c c e p t a b l e . I n a l l o t h e r cases t h e accommodated s i n g l e f a i l u r e t r a n s i e n t per formance was good.
The second exper iment demonst ra ted t h e e x c e l - l e n t accuracy o f t h e eng ine model. I n t h i s e x p e r i ment, f i r s t a l l t h e eng ine sensors were f a i l e d and accommodated. Then, a PLA p u l s e t r a n s i e n t was genera ted f rom i d l e t o about 7 5 pe rcen t o f f u l l power. R e s u l t s f o r N1 and P l 6 a r e shown i n F i g . 6. Again e x c e l l e n t per formance was demonst ra ted. L i t - t l e o r no ove rshoo t was observed and eng ine s teady- s t a t e per formance was good. T h i s demonst ra tes t h e c a p a b i l i t y o f sa fe , p r e d i c t a b l e eng ine o p e r a t i o n w i t h o u t any eng ine feedback i n f o r m a t i o n over a broad power range.
Conc lus ions - .
Based on r e s u l t s o f eng ine t e s t s ob ta ined so f a r , s e v e r a l p r e l i m i n a r y c o n c l u s i o n s have been reached. F i r s t , i t can be conc luded t h a t t h e ADIA f a i l u r e d e t e c t i o n a l g o r i t h m works q u i t e w e l l . Sen- so r f a i l u r e d e t e c t i o n and accommodation were demon s t r a t e d a t two power c o n d i t i o n s . The minimum d e t e c t a b l e f a i l u r e magnitudes r e p r e s e n t e x c e l l e n t a l g o r i t h m per formance and compare f a v o r a b l y t o v a l - ues p r e d i c t e d by s i m u l a t i o n . Accommodation p e r - formance was e x c e l l e n t . T r a n s i e n t eng ine o p e r a t i o n over t h e f u l l power range w i t h s i n g l e sensors f a i l e d and accommodated was s u c c e s s f u l l y demonst ra ted. Open l oop eng ine o p e r a t i o n ( a l l sensors f a i l e d and accommodated) over 75 pe rcen t o f t h e power range was a l s o demonst ra ted. Second, t h e a l g o r i t h m i s implementab le i n a r e a l i s t i c env i ronment and i n an update i n t e r v a l c o n s i s t e n t w i t h s t a b l e eng ine ope r - a t i o n . O f f - t h e - s h e l f m ic rop rocesso r based hardware and s t r a i g h t f o r w a r d programming p rocedu res , i n c l u d - i n g FORTRAN and f l o a t i n g p o i n t a r i t h m e t i c , were used. P a r a l l e l p r o c e s s i n g was a l s o used and shown t o be an e f f e c t i v e approach t o a c h i e v i n g a r e a l - t i m e imp lemen ta t i on u s i n g o f f - t h e - s h e l f ( c o s t e f f e c t i v e ) computer resou rces . F i n a l l y , i t i s conc luded t h a t t h e demonst ra ted h i g h per formance d e t e c t i o n , i s o l a - t i o n , and accommodation c a p a b i l i t i e s o f t h e ADIA a l g o r i t h m j u s t i f i e s f u r t h e r demons t ra t i on t h roughou t t h e f l i g h t enve lope. Pending t h e a n t i c i p a t e d suc- c e s s f u l outcome o f t h e a d d i t i o n a l demons t ra t i on t e s t i n g , a f l i g h t t e s t e v a l u a t i o n may be j u s t i f i e d as f u t u r e work.
References - -
1. Baker, L.E., Warner, D.E., and D i s p a r t e , C.P., "Des ign o f F a u l t T o l e r a n t E l e c t r o n i c Engine C o n t r o l s , " AIAA Paper 81-1496, J u l y 1981.
2. M e r r i l l , W . C . , "Sensor F a i l u r e D e t e c t i o n f o r J e t Engines Us ing A n a l y t i c a l Redundancy," Jou rna l - o f GuidanceI C o n t r o l and Dynamics, Vo l . 8, No. 6, Nov.-Dec. 1985, pp. 673-682.
3 . B e a t t i e , E.C., Laprad, R . F . , McGlone, M.E., Rock, S.M., and Akh te r , M.M., "Sensor F a i l u r e D e t e c t i o n System - f o r t h e FlDO Turbofan Eng ine, " PWA 5736-17, P r a t t and Whitney Air- c r a f t , East H a r t f o r d , C T , Aug. 1981. (NASA CR-165515 . )
4 . B e a t t i e , E . C . , Laprad, R . F . , Akh te r , M . M . , and Rock, S.M., "Sensor F a i l u r e D e t e c t i o n f o r J e t Eng ines, " PWA 5891-18, P r a t t and Whitney A i r -
H a r t f o r d , CT, May 1983. (NASA c r a f t , East CR-168190.)
5. De laa t , J.C. Implementa t D e t e c t i o n . A l g o r i t h m , " ( A l s o , NASA
and M e r r i l l , W . C . , " A Real-Time i o n o f an Advanced Sensor F a i l u r e I s o l a t i o n and Accommodation AIAA Paper 84-0569, Jan. 1984. TM-83553 . )
6 . M e r r i l l . W . C . , and DeLa t t , J.C., "A Real-Time S i m u l a t i o n E v a l u a t i o n o f an Advanced D e t e c t i o n , I s o l a t i o n and Accommodation A l g o r i t h m f o r Sensor F a i l u r e s i n T u r b i n e Eng ines, " NASA 1M-87289, 1986.
7 . M e r r i l l , W . C . , DeLa t t , J.C., and B ru ton , W . , "Advanced D e t e c t i o n , I s o l a t i o n , and Accommoda- t i o n o f Sensor F a i l u r e s - Rea l -T ime E v a l u a t i o n , " NASA TP- , 1987. (To be p u b l i s h e d . )
8. Soeder, J.F., "F-100 M u l t i v a r i a b l e C o n t r o l Syn thes i s Program - Computer Imp lemen ta t i on o f t h e F-100 M u l t i v a r i a b l e C o n t r o l A l g o r i t h m , " NASA 1P-2231, 1983.
9 . Le th inen , B. , Cos tak i s , W . G . , Soeder, J .F . , and Se ldne r , K . , "F-100 M u l t i v a r i a b l e C o n t r o l Syn thes i s Program - R e s u l t s o f Eng ine A l t i t u d e Tes ts , " NASA TM 5-83367, 1983.
10. DeLa t t , J.C., Soeder, J.F., "Design o f a Microprocessor -Based C o n t r o l , I n t e r f a c e , and M o n i t o r i n g (CIm) U n i t f o r Tu rb ine Engine C o n t r o l s Research," NASA TM-83433, 1983.
11. Melcher , K .J . , DeLaat, J.C., M e r r i l l , W.C. , Ober le , L.G., Schaefer , J.H., and Sad le r , G . G . , "A Sensor F a i l u r e S i m u l a t o r f o r C o n t r o l System R e l i a b i l i t y S t u d i e s , " NASA TM-87271, 1986.
TABLE 1 . - HARD DETECTION
THRESHOLD UAGNITUOES
- PLA
- 50
80
Sensor
F T I T
d e v l a t l o n
Name
TABLE 2. - TEST DEFINITIONS
Sensor f a l l u r e s Hard
S o f t
D r l f t
SSF
PLA t r a n s i e n t s P u l s e
S l n g l e
Open
D e s c r l p t l o n
Large magn l tude ( h a r d ) b l a s f a l l u r e 1s Induced.
Smal l magn l tude ( s o f t ) b l a s f a l l u r e I s l n d u c e d .
Smal l magn l tude ( s o f t ) d r l f t f a l l u r e I s l n d u c e d .
4 sequence o f s u c c e s s l v e sensor f a l l u r e s I s lnduced.
I d l e t o l n t e r m e d l a t e t o I d l e t r a n s l e n t PLA e x c u r s l o n s . The l n t e r m e d l a t e power l e v e l I s m a i n t a i n e d f o r 1 0 sec.
P u l s e t e s t w l t h a s l n g l e sensor f a l l u r e accomnodated b e f o r e l n l t l a t l n g t h e t r a n s l e n t .
Same as t h e P u l s e t e s t e x c e p t t h a t t h e mlnlmum power l e v e l I s r a l s e d s l l g h t l y and t h e maxlmum power l e v e l I s decreased s l l g h t l y and t h e e n g l n e I s c o n t r o l l e d w l t h o u t u s i n g any sensed e n g l n e o u t p u t l n f o r m a t l o n I n t h e c o n t r o l , l . e . , a l l sensors f a l l e d .
TABLE 3. - nINlnun OEIECTABLE BIAS ANO DRIFT FAILURE MAGNITUDES
[ A l t l t u d e = 10 K, Mach = 0.6.1
;ensor IMlnlmum detectable blas f a t l u r e / \ Mlnlmum detectable d r l f t f a l l u r e
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