邢唷 > ! D " t h a t a n e x t e r n a l t i m e r b e u s e d i n c o n j u n c t i o n w i t h t h e S o u r c e M e t e r . T h e t i m e s t a m p s h o u l d o n l y b e u s e d t o a p p r o x i m a t e t h e a m o u n t o f t e s t t i m e r e q u i r e d . T h e m e t h o d i n w h i c h t h e t i m e s t a m p i s i m p l e m e n t e d l i m i t s i t s u s e i n t i m e - c r i t i c a l a p p l i c a t i o n s . I f a c c u r a t e e x p e r i m e n t t i m i n g i s c r u c i a l , i t i s r e c o m m e n d e d t h a t a n e x t e r n Using the Model 2400 Internal Timestamp Feature
The Model 2400 Series of SourceMeter instruments allows the user to retrieve a timestamp with each reading sent over the GPIB.
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` l t | 0 Using the Model 2400 Internal Timestamp Feature sin Doug Rathburn l oug Normal t Doug Rathburn l 5 ug Microsoft Word 8.0 0@ xA @ :=滂@ 玷 p % 犎階 < @ 0 4 - 5 4 B 6 - 1 1 D 3 - 8 5 0 2 - 0 0 6 0 9 7 B 5 0 B D R B" D" " R& & ' ' ' CJ OJ QJ 6丆J OJ QJ j \餋J OJ QJ CJ OJ QJ 0 1 l n @ B R T V l n ! ! ! ! @" 勑 o b l e m i f t i m i n g i n f o r m a t i o n i s c r i t i c a l .
T h e r e s u l t i s t h a t t h e S o u r c e M e t e r l o s e s 2 4 m s f o r e v e r y s e c o n d o f t e s t t i m e !
T o g e t a n u m b e r c l o s e r t o t h e a c t u a l t e s t t i m e , m u l t i p l y t h e t i m e s t a m p r e s u l t b y 9 . 7 6 5 6 2 5 e - 4 . T h e t i m e s t a m p s h o u l d o n l y b e u s e d t o a p p r o x i m a t e t h e a m o u n t o f t e s t t i m e r e q u i r e d . T h e m e t h o d i n w h i c h t h e t i m e s t a m p i s i m p l e m e n t e d l i m i t s i t s u s e i n t i m e - c r i t i c a l a p p l i c a t i o n s . I f a c c u r a t e e x p e r i m e n t t i m i n g i s c r u c i a l , i t i s r e c o m m e n d e d t h a t a n e x t e r n a l t i m e r b e u s e d i n c o n j u n c t i o n w i t h t h e S o u r c e M e t e r .
T h e t i m e s t a m p i s b a s e d o n a 8 k H z o s c i l l a t o r . T h i s o s c i l l a t o r i s u s e d a s t h e s y s t e m c l o c k a n d t o g e n e r a t e s y s t e m t i c k s e v e r y m i l l i s e c o n d . T h e r e f o r e , t h e t i m e s t a m p s h o u l d p r o v i d e 1 m s r e s o l u t i o n f o r t e s t t i m i n g . T h e p r o b l e m i s t h a t t h e o s c i l l a t o r i s n o t e x a c t l y 8 k H z , b u t i t i s r a t h e r 8 1 9 2 H z . T h e c a l c u l a t i o n s a r e b e l o w :
T h e s y s t e m c l o c k i s d i v i d e d b y 8 t o d e t e r m i n e w h e n s y s t e m t i c k s o c c u r .
8 1 9 2 H z / 8 = 1 0 2 4
T h i s i m p l i e s t h a t a s y s t e m t i c k i s g e n e r a t e d 1 0 2 4 t i m e s e v e r y s e c o n d .
( T h i s r e s u l t s i n a s y s t e m t i c k e v e r y 9 . 7 6 5 6 2 5 e - 4 s e c o n d s !
S i n c e t h e i n s t r u m e n t d o e s n o t w a n t t o p e r f o r m t h e m a t h t o g e n e r a t e t i m e s t a m p d u r i n g e v e r y r e a d i n g , t h e m i c r o p r o c e s s o r o n l y c o u n t s s y s t e m t i c k s . I f t h e t i m e s t a m p i s t o b e r e p o r t e d o v e r t h e f r o n t p a n e l o r b u s , t h e m i c r o p r o c e s s o r r e p o r t s t h e n u m b e r o f s y s t e m t i c k s a s t h e n u m b e r o f m i l l i s e c o n d s f o r t h e m e a s u r e m e n t . T h e d i f f e r e n c e b e t w e e n t h e n u m b e r o f s y s t e m t i c k s a n d t h e a m o u n t o f t i m e a c t u a l l y e l a p s e d c a n p o s e a p r o b l e m i f t i m i n g i n f o r m a t i o n i s c r i t i c a l .
T h e r e s u l t i s t h a t t h e S o u r c e M e t e r l o s e s 2 4 m s f o r e v e r y s e c o n d o f t e s t t i m e !
T o g e t a n u m b e r c l o s e r t o t h e a c t u a l t e s t t i m e , m u l t i p l y t h e t i m e s t a m p r e s u l t b y 9 . 7 6 5 6 2 5 e - 4 .
D . R a t h b u r n 8 - 1 7 - 9 9 0 B D R B" D" " R& & ' ' ' * * 苎 j 茵CJ H*OJ QJ 5丆J CJ OJ QJ 6丆J OJ QJ j \餋J OJ QJ CJ OJ QJ @" B" " " R& T& V& & ' ' ' ' ' ' ' ' ' ' ' ' 勑 a l t i m e r b e u s e d i n c o n j u n c t i o n w i t h t h e S o u r c e M e t e r .
T h e t i m e s t a m p i s b a s e d o n a 8 k H z o s c i l l a t o r . T h i s o s c i l l a t o r i s u s e d a s t h e s y s t e m c l o c k a n d t o g e n e r a t e s y s t e m t i c k s e v e r y m i l l i s e c o n d . T h e r e f o r e , t h e t i m e s t a m p s h o u l d p r o v i d e 1 m s r e s o l u t i o n f o r t e s t t i m i n g . T h e p r o b l e m i s t h a t t h e o s c i l l a t o r i s n o t e x a c t l y 8 k H z , b u t i t i s r a t h e r 8 1 9 2 H z . T h e c a l c u l a t i o n s a r e b e l o w :
T h e s y s t e m c l o c k i s d i v i d e d b y 8 t o d e t e r m i n e w h e n s y s t e m t i c k s o c c u r .
8 1 9 2 H z / 8 = 1 0 2 4
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( T h i s r e s u l t s i n a s y s t e m t i c k e v e r y 9 . 7 6 5 6 2 5 e - 4 s e c o n d s !
S i n c e t h e i n s t r u m e n t d o e s n o t w a n t t o p e r f o r m t h e m a t h t o g e n e r a t e t i m e s t a m p d u r i n g e v e r y r e a d i n g , t h e m i c r o p r o c e s s o r o n l y c o u n t s s y s t e m t i c k s . I f t h e t i m e s t a m p i s t o b e r e p o r t e d o v e r t h e f r o n t p a n e l o r b u s , t h e m i c r o p r o c e s s o r r e p o r t s t h e n u m b e r o f s y s t e m t i c k s a s t h e n u m b e r o f m i l l i s e c o n d s f o r t h e m e a s u r e m e n t . T h e d i f f e r e n c e b e t w e e n t h e n u m b e r o f s y s t e m t i c k s a n d t h e a m o u n t o f t i m e a c t u a l l y e l a p s e d c a n p o s e a p r S e r i e s i n g ( @" B" " " R& T& V& & ' ' ' ' ' ' ' ' ' ' ' ' 勑 / U s i n g t h e M o d e l 2 4 0 0 I n t e r n a l T i m e s t a m p F e a t u r e
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