ESI VideoBridge 2150, Service Manual

Page: 71 / 332

2 . 3 � 4 Test-Leads
vs
Tes t-F i x tures
C e r ta i n m e a s u remen t a re a s a re more c r i t i ca l t ha n o th e r s a n d requ i re
the u s e o f a t e s t- f i x t u r e ra t h e r t h a n t e s t- l ea d s . Tes t- l ea d s w i t h
K EL V I N K L I P S a re be s t u s e d a t f requ e n c i e s be l ow 1 k H z o r f or h i g he r
f re q u e n c y me a s u reme n t s w he r e h i g h a c cura cy i s n o t n e e de d ( s e e n o t e
a t ta c he d t o K E L V I N KL I PS ) . C ha n g e s i n t e s t- l e a d p o s i t i on c h a n g e s t ra y
capa c i ta n ce a nd/or i nd u c ta n c e , mak i n g a t rue z e ro c o r re c t i on d i f f i cu l t
to o b ta i n .
A t h i g h e r f r e q u e n c i e s ( a b o v e 1 k H z ) , t h e n e e d f o r a t e s t - f i x t u r e
be c o m e s m o r e a n d m o r e i mp o r t a n t b e c a u s e t e s t - l e a d ( K L I P ) s p a c i n g
c a n n o t b e f i x e d a s i n a t e s t - f i x t u r e . I f
mea s u remen t s a re n e e d e d , u se a t e s t- f i x tu r e .
A l s o , i f d i f f e re n t t e s t l e a d l e n g t h s a r e u s e d ( fo r e xamp l e , c h a n g i n g
f r om 5 f oo t l ea d s t o 3 f oo t l e a ds ) , t he h i g h f requ e n cy t r i m m a y h a ve
to be re- a d j u s t e d . S e e S e c t i on 4 . 2 f o r more i n f o rma t i on on t h i s t r i m
•
2 . 3 . 5 Te s t F i x ture C a l i bra t ion
Mea s u reme n t a c cura c y i s e n ha nc e d by t h e 2 1 5 0 / 2 1 6 0 ' s a b i l i ty to cor r e c t
f o r z e ro- o f f se t e rrors c a u s e d by t e s t- l e a d a n d t e s t- f i x tu re i mp e d a n c e s
( i n d u c ta n c e , re s i s ta n c e , c a pa c i t a n c e , e t c . ) . T h e s e i mpeda n ce s a pp e a r
i n p a ra l l e l o r i n s e r i e s w i th t he u n k n ow n comp o ne n t d u r i ng mea su reme n t
a n d a d d t o t h e m e a s u r e d va l u e . T h e z e r o ca l i bra t i on f u n c t i on m e a s u re s
t he s e z e r o o f f se t e r rors a nd s t ore s them i n memory . The s t ored va l ue
i s a u toma t i ca l ly s u b t ra c te d f rom e a c h mea s u re d va l ue .
The 2 1 5 0 / 2 1 6 0 can s tore o f f se t m e a s u reme n t s f o r f ou r d i f f e re n t
combi na t i ons o f se t t i ng s f o r : t e s t f requ e n c y , t e s t s i g n a l , i n te g ra t i on
t ime , s e t t l i ng t ime a n d mea s u r e me n t s a ve ra g e d . On c e t h e s e o f f s e t s have
been me a su r e d for a g i ve n combi na ti on , the Vi deoBr i dg e w i l l re t r i e ve
t he m w he ne v e r t h a t comb i na t i on is r e - e n t e re d . T h e word " CAL I B " w i l l
be d i sp la y e d t o i nd i ca t e t h a t t h i s combi n a t i on ha s be e n ca l i br a t e d .
2 - 3 2
e l s l i 2 1 5 0 / 2 1 6 0 9 / 8 5
•