ESI VideoBridge 2150, Service Manual

Page: 70 / 332

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2 . 3 . 3 C o n ne c t i ons
to
Unknown
Mode l s 2 1 5 0 / 2 1 6 0 make
f ou r- t e r m i na l mea sureme n t s
w i t h pa s s i ve
g u a rd i ng . T h e y pro v i de s e pa ra te s h i e l d e d conne c t i on c a b l e s f o r c u r re n t
d r i ve a n d v o l t a g e s e n s e t o t h e h i g h a n d l ow s i d e o f t he u n k n own . T h e s e
c a b l e s a re f u l l y s h i e l d e d t o m i n i m i z e t he e f fe c t s o f s t ra y capa c i ­
t a n ce . T h ey a re la be l e d H I D R I V E , H I S E N S E , L O DR I VE , a n d L O S E NS E .
T h e s h i e l d s a round t he H I G H a n d LOW D R I V E c a b l e s a re c o n n e c t ed to t he
GUARD po i n t ( se e F i g u re 2 - 8 ) . T h e to ta l l oa d i mp e d a n c e
( Z )
t o t he
g u a r d po i n t mus t be g re a t e r t h a n o r egua 1 t o t h e i mpeda n c e o f t h e
d e v i c e u n d e r t e s t . D r i v e a n d s e n s e l e a d s f o r b o t h H I G H a n d L OW
t e rm i na l s mu s t make s e pa r a t e c onne c t i on s t o the u n k n ow n .
HI D RI V E H I SE N S E
,
,
�"',
Z LOAD','
HI TO GUARD
�{
,
,
, "
LO SE NSE
"
"
,-"
, .
," ,," Z LOAD
LO DRIVE
/';
LO TO GUARD
"
*Guard shields of H I and LO D ri v e
ccble� must b e connected a t
unknown e n d of test-leads .
GUARD*
F i gure 2-8 . Conne c t i on
to
Unknow n
For a c c u ra te mea su reme n ts of l ow i mpeda n c e u nk n o w n s , sepa ra te d ri ve
and sense c o n ne c t i o n s a re n e c e s s a ry to pre v e n t l e a d r e s i s t a n c e f rom
b e c o m i n g a p a r t o f t h e m e a s u r e d u n k n o w n . B o t h d r i v e a n d s e n s e
c o n n e c t i o n s c a n be c on ne c t e d toge t h e r t o a s i ng l e l e a d o f t h e u nk n own
( a 2 - t e rm i na l m e a s u re m e n t ) i f t h e l ea d i s a s ma l l pa r t of t he unk nown
imped a n c e ( R l d <
Z
k/ l O O O f o r < 0 . 1 % e r r o r ) . W i th p r ope r c on n e c t i on s
e a u n
a s s h o w n i n F i g u r e 2 - 8 , c a b l e l e n g t h o f 5 f e e t c a u s e s n o l o s s o f
a c c u r a c y . D i f f e r e n t c a b l e l e n g t h s o r s p e c i a l t e s t c o n d i t i o n s m a y
re s u l t i n a c cu ra cy l o ss .
C o n su l t E S I f a c tory f o r a dv i c e on y o u r app l i c a t i o n .
2 - 3 1
e l s l i 2 1 5 0 / 2 1 60 5 /8 5