ICROPROCESSOR APPLICATlO E

I n t r o d u c t i o n

T h e Electr ical E n g i n e e r i n g Technology program a t t h e U n i v e r s i t y o f Tennessee a t Martin p r o v i d e s a broad base of t e c h n i c a l knowledge f o r i t s g r a d u a t e s . To t h i s end emphas is is p l a c e d on a number o f a r e a s w i t h i n t h e d i s c i p l i n e , i n c l u d i n g e l e c t r o n i c s , communicat ions, power d i s t r i b u t i o n , and d i g i t a l d e v i c e s . It is i n t e n d e d t h a t t h e g r a d u a t e s be p r o p e r l y t r a i n e d f o r employment i n l i g h t i n d u s t r y p r e v e l a n t i n t h e r e g i o n or i n t h e l o c a l power d i s t r i b u t i o n u t i l i t i e s .

D e s c r i p t i o n of Courses

The power d i s t r i b u t i o n f i e l d is examined i n a y e a r - l o n g sequence of c o u r s e s i n t h e s e n i o r y e a r . I n c l u d e d among t h e many t o p i c s examined a r e sys tem e f f i c i e n c y and l o s s e s , main tenance o f sys tem i n t e g r i t y , p r o t e c t i o n d e v i c e s and t h e i r c o o r d i n a t i o n , and cus tomer r e l a t i o n s . An i n t e g r a l p a r t o f t h e c o u r s e i s t h e l a b o r a t o r y u s e o f a power d i s t r i b u t i o n system s i m u l a t o r c o n s t r u c t e d by Hampden E n g i n e e r i n g C o r p o r a t i o n . T h i s d e v i c e s i m u l a t e s a power d i s t r i b u t i o n sys tem from g e n e r a t i o n t o u s e and i n c l u d e s such f e a t u r e s a s m u l t i p l e p a r a l l e l g e n e r a t o r s ; m u l t i p l e t r a n s m i s s i o n p a t h s ; and t y p i c a l l o a d s and t ime-of -day p a t t e r n s f o r r e s i d e n t i a l , i n d u s t r i a l , commercial , and a g r i c u l t u r a l cus tomers . Also i n c l u d e d a r e s e v e r a l i n s t r u c t o r - i n s e r t a b l e f a u l t s which i l l u s t r a t e t h e i r system-wide e f f e c t and t h e impor tance of p r o p e r l y c o o r d i n a t e d p r o t e c t i o n d e v i c e s . A l l c o n t r o l l a b l e v a r i a b l e s and s w i t c h e s can be o p e r a t e d both manual ly and a u t o m a t i c a l l y . Automatic c o n t r o l can be accompl ished e i t h e r by timer c o n t r o l l e d c o n t a c t s w i t c h i n g , or by c o n t a c t c l o s u r e on a panel d e s i g n e d t o a l l o w computer i n t e r f a c i n g . It is t h i s computer i n t e r f a c i n g p a n e l which makes t h e simulator so u s e f u l as an i n t e r d i s c i p l i n a r y t r a i n i n g a i d .

The a r e a of d i g i t a l d e v i c e s is a l s o i n v e s t i g a t e d i n a y e a r - l o n g sequence of c o u r s e s i n t h e s e n i o r y e a r . The f i r s t two q u a r t e r s are devoted t o such t o p i c s as g a t e s , f l i p - f l o p s , c o u n t e r s , memory d e v i c e s and A / D and D / A d e v i c e s . The l a s t h a l f o f t h e second c o u r s e b e g i n s an examinat ion of m i c r o p r o c e s s o r s , wi th

Ottis L. Barron Associate Professor Engineer ing Technology The U n i v e r s i t y o f Tennessee

Martin, Tennessee a t Martin

emphasis on t h e 6800 series. It is i n t h e t h i r d c o u r s e , which c o n c e n t r a t e s on m i c r o p r o c e s s o r a p p l i c a t i o n s , t h a t u s e is made of the power d i s t r i b u t i o n s i m u l a t o r .

The P r o j e c t

S i n c e one of t h e major o b j e c t i v e s o f t h e m i c r o p r o c e s s o r a p p l i c a t i o n c o u r s e is t o deve lop t h e s t u d e n t ' s a b i l i t y t o u s e t h e m i c r o p r o c e s s o r as a t o o l i n s o l v i n g a v a r i e t y of problems, e x t e n s i v e u s e is made of p r o j e c t ass ignments . These ass ignments r e q u i r e t h e a p p l i c a t i o n of knowledge o b t a i n e d from a number of c o u r s e s , i n c l u d i n g perhaps e l e c t r o n i c s , communicat ions, and power d i s t r i b u t i o n . I n o r d e r t o e s t a b l i s h t h e i n t e r d e p e n d e n c e of t h e v a r i o u s s u b j e c t a r e a s i n e l e c t r i c a l e n g i n e e r i n g t e c h n o l o g y , one p r o j e c t ass ignment makes s p e c i f i c u s e of t h e power d i s t r i b u t i o n s i m u l a t o r . T h i s ass ignment r e q u i r e s t h e u s e of a m i c r o p r o c e s s o r t o c o n t r o l t h e f requency a n d / o r v o l t a g e of a 600 v o l t g e n e r a t o r .

Both g e n e r a t o r o u t p u t v o l t a g e and f requency a r e a v a i l a b l e a t t h e computer i n t e r f a c e p a n e l , b u t cannot be used d i r e c t l y because of incompatable v o l t a g e l e v e l s . The g e n e r a t o r o u t p u t of 600 v o l t s is s c a l e d t o 120 v o l t s a.c. a t t h e i n t e r f a c e . It is n e c e s s a r y t o c o n v e r t t h i s v o l t a g e t o a d i g i t a l form f o r u s e by t h e m i c r o p r o c e s s o r . The trainer boards used i n t h e l a b (Heath Model ET-3400) o p e r a t e on s t a n d a r d TTL v o l t a g e l e v e l s (0-5 v o l t s d . c . ) , so t h e s t u d e n t s must c o n d i t i o n t h e s i g n a l b e f o r e it can be used. ADC0809 a n a l o g - t o - d i g i t a l c o n v e r t e r (ADC) c i r c u i t s a r e used t o o b t a i n a d i g i t a l e q u i v a l e n t of t h e ana log v o l t a g e a f t e r it h a s been c o n v e r t e d t o a 0-5 v o l t d.c. s i g n a l . The approach u s u a l l y used is t o t r a n s f o r m t h e 120 v o l t s a .c . t o a lower v o l t a g e , then r e c t i f y and filter it t o o b t a i n a d.c. v o l t a g e . T h i s v o l t a g e is then s c a l e d t o o b t a i n t h e d e s i r e d g e n e r a t o r - t o - d . c . v o l t a g e r a t i o .

Once t h e p r o p e r d .c . v o l t a g e r a n g e is o b t a i n e d , t h e s i g n a l is c o n v e r t e d t o i ts d i g i t a l e q u i v a l e n t by t h e ADC0809. T h i s d e v i c e h a s 8 ana log i n p u t l i n e s . The p r o p e r l i n e is s e l e c t e d by a p p l y i n g t h r e e b i n a r y i n p u t s t o a p p r o p r i a t e p i n s on t h e device . If o n l y one ana log i n p u t

62 CH 1829-1/82/0000-0062 $00.75 @ 1982 IEEE 1 982 FRONTIERS IN EDUCATION CONFERENCE PROCEEDINGS

is used , t h e p r o p e r l i n e may be s e l e c t e d by h a r d w i r i n g t h e t h r e e l o g i c i n p u t s t o a p p r o p r i a t e l o g i c v o l t a g e s . The s t u d e n t must a l s o p r o v i d e t h e p r o p e r s i g n a l s t o i n i t i a t e t h e c o n v e r s i o n p r o c e s s and o u t p u t t h e d i g i t a l s i q n a l t o t h e mic roprocesso r .

Once t h e d i g i t a l v a l u e is o b t a i n e d , it must b e compared w i t h t h e nominal g e n e r a t o r v o l t a g e v a l u e t o d e t e r m i n e what , i f any, a c t i o n s h o u l d be t aken . The s t u d e n t must d e t e r m i n e t h e d e s i r e d c o n t r o l a c t i o n and deve lop t h e n e c e s s a r y machine l anguage programs t o implement t h i s a c t i o n . Using t h e p r e v i o u s l y e s t a b l i s h e d g e n e r a t o r - t o - d i g i t a l r d t io , t h e d i g i t a l e q u i v a l e n t o f t h e maximum and minimum g e n e r a t o r v o l t a g e is de te rmined . The m i c r o p r o c e s s o r program compares t h e a c t u a l d i g i t a l v a l u e t o t h e s e limits and, i f n e c e s s a r y , b ranches t o a program t o raise or lower t h e v o l t a g e .

The g e n e r a t o r v o l t a g e is changed by comple t ing t h e c i r c u i t between two t e r m i n a l s on t h e s i m u l a t o r i n t e r f a c e . T h i s change is accompl i shed w i t h r e l a y c o n t a c t s which are c o n t r o l l e d by t h e mic roprocesso r . A p e r i p h e r i a l i n t e r f a c e a d a p t e r (PIA) c h i p is used t o c o n n e c t t h e m i c r o p r o c e s s o r bus t o 5 v o l t r e l a y s , one t o p r o v i d e f o r i n c r e a s i n g t h e g e n e r a t o r e x c i t a t i o n v o l t a g e and one t o d e c r e a s e it. Once a c t i v a t e d t h e r e l a y c o n t a c t s remain c l o s e d u n t i l t h e g e n e r a t o r v o l t a g e a g a i n f a l l s w i t h i n t h e a c c e p t a b l e r ange . F i g u r e 1 i l l u s t r a t e s t h e i n t e r c o n n e c t i o n s r e q u i r e d between t h e m i c r o p r o c e s s o r (MPU), t h e PIA, t h e ADC, and t h e r e l a y s . F i g u r e s 2 and 3 show t h e r e l a y c o n t r o l c i r c u i t s and t h e a .c . - to-d.c . c o n v e r t e r c i r c u i t r e s p e c t i v e l y .

A s o u t p u t v o l t a g e changes it a l s o a l te rs g e n e r a t o r c u r r e n t . (4 c u r r e n t change i n t u r n r e s u l t s i n a v a r i a t i o n l i n f r equency . Frequency d i s c r e p a n c i e s c a n b e c o r r e c t e d by r a i s i n g or lower ing t h e f i e l d va3ltage o f t h e motor which d r i v e s t h e g e n e r a t o r i n a manner s i m i l a r t o t h a t

E E ADDRESS BUS

+----------"\I

used t o c o n t r o l t h e g e n e r a t o r e x c i t a t i o n v o l t a g e . The o u t p u t f r equency is compared t o upper and lower l i m i t i n g v a l u e s and c o r r e c t i v e a c t i o n is t a k e n i f necessd ry .

S i n c e t h e s i g n a l f r equency is so low (60 Hz. ) , t h e p e r i o d r a t h e r t han t h e f r equency i t s e l f is measured. The waveform is f i r s t c o n v e r t e d t o a s q u a r e wave. T h i s s i g n a l is then r o u t e d t o a PIA i n p u t which r e sponds t o v o l t a g e l e v e l changes. A c o u n t i n g r o u t i n e is i n i t i a t e d on one t r a n s i t i o n and t h e c o u n t e r is read on t h e nex t change. Making u s e o f t h e time r e q u i r e d f o r t h e program t o inc remen t Lhe c o u n t e r by one c o u n t , one can de te rmine t h e t o t a l e l a p s e d time between t r a n s i t i o n s . I n t h i s manner t h e c o u n t e r t o t a l c o r r e s p o n d i n g t o t h e d e s i r e d f r equency can be de t e rmined . Accep tab le v a r i a t i o n s i n f r equency de te rmine t h e upper and lower c o u n t e r limits. Counts o u t s i d e t h e limits c a u s e b ranch ing t o routines which c l o s e t h e a p p r o p r i a t e r e l a y c o n t a c t s which r e s u l t s i n i n c r e a s i n g or d e c r e a s i n g t h e f i e l d v o l t a g e , which i n t u r n moves t h e f r equency toward t h e d e s i r e d set p o i n t . The f r equency i n p u t is shown on F i g u r e 1. The r e l a y c o n t r o l c i r c u i t of F i g u r e 2 i s used t o c o n t r o l t h e f i e l d v o l t a g e changes.

C o n c l u s i o n s

The m i c r o p r o c e s s o r p r o j e c t a s s ignmen t s r e s u l t i n an i n c r e a s e d l e v e l o f s t u d e n t s e l f - c o n f i d e n c e . Although i n t i t a l l y bewi lde red by t h e complex i ty o f t h e problem, t h e s t u d e n t soon realizes t h a t it is j u s t a combinat ion of a number o f s m a l l e r problems. He is f o r c e d t o make use o f h i s bank o f knowledge f rm s e v e r a l a r e a s o f e l e c t r i c a l e n g i n e e r i n g technology. A t t h e comple t ion o f t h e p r o j e c t , t h e s t u d e n t g e n e r a l l y e x p r e s s e s p r i d e and s a t i s f a c t i o n i n h i s a b i l i t y t o make use o f h i s knowledge, and an i n c r e a s e d awareness t h a t t h e i n d i v i d u a l areas of s t u d y do n o t exist i n a vacuum, b u t a r e a c t u a l l y c l o s e l y i n t e r r e l a t e d .

ADC 3

MPU

C13NTROL BUS CA1

ANALOG INPUT SELECT

FREQUENCY

Figure 1: Hardware Interconnection Diagram

ADD. LATCH

_. ~ ~

CONTROL CIRCUITS ANALOG INPUT

1 982 FRONTIERS IN EDUCATION CONFERENCE PROCEEDINGS 6 3

SIMULATOR INTERFACE PANEL CONNECTORS

STEPDOWN /\ TRANSFORMER

P

D.C. OUTPUT

Y O m o N

LVh'ER

" P

FROM w PORT B RELAY DRIVERS LINES

F i g u r e 2 : R e l a y C o n t r o l For S i m u l a t o r A d j u s t m e n t

F igure 3 : A.C.- to-D.C. C o n v e r t e r

64 1982 FRONTIERS IN EDUCATION CONFERENCE PROCEEDINGS

r' An A s s o c i a t e P r o f e s s o r of E l e c t r i c a l E n g i n e e r i n g Technology a t t h e U n i v e r s i t y of Tennessee a t M a r t i n , D r . Bar ron r e c e i v e d h i s B.S.E.E. from L o u i s i a n a S t a t e U n i v e r s i t y and h i s M.S. and Ph.D. from M i s s i s s i p p i S t a t e U n i v e r s i t y . He i s a c t i v e i n I E E E , h a v i n g s e r v e d a s f a c u l t y a d v i s o r f o r t h e UTM S t u d e n t Chapter and a s v i c e p r e s i d e n t of t h e J a c k s o n , Tennessee , S u b - s e c t i o n . H~ has also p r e s e n t e d p a p e r s a t s e v e r a l r e g i o n a l m e e t i n g s . He i s e s p e c i a l l y i n t e r e s t e d i n m i c r o p r o c e s s o r a p p l i c a t i o n s . D r . Bar ron was a f i e l d e n g i n e e r w i t h A u t o n e t i c s D i v i s i o n of Rockwell and h a s p a r t i c i p a t e d i n summer p r o j e c t s w i t h I T T , t h e M i s s i s s i p p i T e s t F a c i l i t y and t h e ASEE-NASA Summer F a c u l t y R e s e a r c h Program.

1 982 FRONTIERS IN EDUCATION CONFERENCE PROCEEDINGS 65