The assessm en t of i n d i v i d u a l c i r c u i t performance and t h a t of com plete in stru m e n ts was a n e c e s s a r y and i n t e g r a l p a r t o f t h e s t u d y . The f in d i n g s of such a sse s sm e n ts were in v a lu a b le in o p ti m i z i n g i n d i v i d u a l c i r c u i t p a r a m e t e r s , and i n d e t e r m i n i n g t h e i n t e r a c t i v e e f f e c t s o f combining t h e s e c i r c u i t s i n t o working in s tr u m e n ts . S p e c ia l t e s t e q u i p m e n t was c o n s t r u c t e d s o t h a t t h e f u l l r a n g e o f t h e th r e e i m p o r t a n t Le ^ m e t e r p a r a m e t e r s c o u l d be p r e s e n t e d t o t h e instrum ent. As d i s c u s s e d i n C h a p t e r F o u r , t h e p a r a m e t e r s a r e : t h e dynamic s p a n , t h e e x c h a n g e r a t e t o l e r a n c e a n d t h e p e a k f a c t o r c a p a b i l i t y . Each o f t h e s e g i v e s a d d i t i o n a l i n f o r m a t i o n a b o u t a g i v e n c i r c u i t design or i n s t r u m e n t ’s s u i t a b i l i t y t o a c c u r a t e l y i n t e g r a t e th e wide s p a n of p o s s i b l e i n p u t s i g n a l l e v e l s and m e a s u r e m e n t d u r a t i o n s . The m ethod f o r a p p l y i n g t h e s e s i g n a l s and t h e m ethod f o r i n t e r p r e t i n g t h e r e s u l t s i s a l s o given in Chapter Four.
T e s ts w ere c a r r i e d o u t on a number o f d i f f e r e n t m a n u f a c t u r e r s ’ ISLMs, and th e r e s u l t s were compared w ith th o se o b ta in e d using th e h y b r i d Le q meter w hich had been p r o d u c e d a s p a r t o f t h i s p r o j e c t . The r e s u l t s o f th e s e t e s t s w e re r e p o r t e d a t t h e I n s t i t u t e o f A c o u s t i c s S p r i n g Conference 1980. A copy o f the r e l e v a n t e x t r a c t from the p ro cee d in g s i s in cluded in Appendix D. In th e t a b l e of exchange r a t e t o l e r a n c e e r r o r s , the ISLM produced as p a r t of t h i s p r o j e c t i s in s tr u m e n t number 5.
The a s s e s s m e n t p r o c e d u r e s u se d i n t h i s work h a v e i n c l u d e d b o t h t o n e b u r s t and s i n g l e - c y c l e input s i g n a l s . A paper d i s c u s s i n g th e r e l a t i v e m e ri ts of th e two methodologies was p re s e n te d a t the 12th I n t e r n a t i o n a l Congress on A c o u s t i c s , T o r o n t o , 1986 [ 1 9 ] . T h i s p a p e r h i g h l i g h t e d t h e
need f o r s p e c i a l i z e d s i g n a l s o u r c e s , and t h e v a l u e o f t h e s p e c i a l i n t e r f a c e developed f o r th e advanced m icro p ro cesso r-b a se d in s tr u m e n t. The d e d i c a t e d s y s t e m d e v e l o p e d a s p a r t o f t h i s work h a s a s i g n a l t o n o is e r a t i o o f g r e a t e r t h a n 80 dB. T h i s i s t h e l i m i t o f t h e f r e q u e n c y a n a l y s e r which has been a v a i l a b l e . The f i n a l v e r s io n of th e in s tru m e n t has a dynam ic r a n g e i n e x c e s s o f t h i s , and a p p r o a c h i n g t h e 110 dB maximum of the c o n t r o l range of t h e a t t e n u a t o r s . I t i s t h e r e f o r e c l e a r t h a t th e e v a l u a t i o n equipment and procedures need c o n s ta n t u p d a tin g in o rd e r t o c o r r e c t l y a s s e s s th e l a t e s t in s tr u m e n ts .
8.1 Instrum entation
The f o l l o w i n g i n s t r u m e n t a t i o n was used during th e f i n a l asse ssm e n t s t a g e o f t h e p r o j e c t . T h i s a r r a n g e m e n t i s r e p r e s e n t a t i v e o f t h e wide range o f equipment used throughout th e development and e a r l i e r assessm ent s t a g e s of th e work.
1. S p e c i a liz e d t o n e b u r s t g e n e r a t o r d e v e l o p e d a s p a r t o f t h i s work.
2. 2 x Enertec Programmable Function G enerators Type 4431. 3. Marconi MF A tte n u a to r Type TF 2162.
4. Gould D i g i t a l Storage O sc illo sc o p e Type 4035.
5. Bruel & Kjaer High R e so lu tio n S ig n a l Analyser Type 2033. 6. Hewlett Packard P l o t t e r Type 7470A
7. F a r n e l l Dual Power Supply Type LT 30-1.
The E n e r t e c p r o g r a m m a b l e f u n c t i o n g e n e r a t o r s w e re u s e d i n combination, w ith one device d e te rm in in g t h e r e p e t i t i o n r a t e f o r th e
tone b u r s t s e q u e n c e s and t h e o t h e r d e t e r m i n i n g t h e t o n e b u r s t d u r a t i o n a n d s i g n a l f r e q u e n c y . A l t h o u g h t h i s w as an e a s y arrangement t o c o n t r o l , p a r t i c u l a r l y v i a t h e IEEE 488 i n t e r f a c e bus, t h e s i g n a l q u a l i t y and r a n g e o f s i g n a l s was n o t a s g r e a t a s th e d e d ic a te d system developed as p a r t of t h i s work. This l a t t e r system was t h e r e f o r e used fo r a l l measurements o th e r tha n i n i t i a l e v a l u a t i o n s .
CHAPTER NINE