Averaging
T w o c irc u it m e th o d s are usu ally u se d fo r averagin g in ele c tro nic co u nte rs .
O ne is used in th e tim e in te rv a l m e as u re m e n t to c o u n t e ac h tim e in terv al
w ith th e co u n tin g c irc u it an d a cc u m m u la te . L et N be th e n u m b e r o f m e a
su re m e n ts, a n d ±1 c o u n t/\/N is p a rt o f m ea su re m en t p re cisio n . T he o th er
m e th o d is th e on e used in p e rio d m e a su re m en t to fo rm a gate w ith th e
p erio d signal to be m ea su re d to m ea su re th e g ate tim e w ith th e in te rn a l
tim e base. O ne fa c to r o f m e as u re m en t p rec isio n is ±1 c o u n t/N . B o th av erag
ing m e th o d s are u sed to e n h a n c e m e a su re m e n t p re cisio n o f e le c tro n ic c o u n
te rs ; ho w e ve r, th e in h e re n t e rro r fa c to rs in sid e th e in s tru m e n t (p ro p a g a tio n
d ela y tim e d iffe re n c e , S c h m itt trig ge r c irc u it h y stere sis b a n d ) ca n n o t b e
im p ro v e d. T h e re fo re , th e u p p e r lim it o f th e n u m b e r o f effe ctiv e m ea su re
m e n ts acc ru es. In usin g th e av erag ing fu n c tio n , th e ±1 c o u n t erro r m u s t be
g u a ra n te ed to o c c u r at ra n d o m . A c o u n te r u su ally se n ds th e sign al to be
m ea su re d to th e c o u n te r g ate c irc u it c o m p le te ly a sy n c h ro n o u s w ith th e
in te rn a l tim e base a n d th e e rro r can b e re ga rd e d to o c c u r at ra n d o m .
B an d w id th
F o r e le c tro n ic c o u n te rs , n oise is a cause o f c o u n tin g e rro rs a n d m u st be c o n
sid ere d in re la tio n to se n sitiv ity .
T h e b a n d w id th sw itch is u sed to rem o ve th e h ig h -fre q u en c y c o m p o n e n t
(see fig u re b e lo w ) w ith a lo w -pass filte r o f 10 M H z, 5 M H z, e tc . T his fu n c
tio n is usefu l in m e asu re m en t o f o sc illatio n a n d m u ltip lie d w aves in a m u lti
p lie r c irc u it.
C OM -SE P S w itc h
A sw itc h to be se le c te d to su it th e signal to be m e asu re d in tim e inte rv al
m e a s u re m e n t. W h en th is sw itch is set to C O M ., th e sta rt a nd s to p signals
are in te rn a lly c o n n e cte d en a b lin g a tim e in te rv a l m e as u re m en t o n a single
signal. S EP . sw itc h se p arate s th e s ta rt a n d sto p sign als, re q uirin g th e tw o
signals, o f s ta rt a n d s to p , to b e m e as u re d . (C O M : C o m m o n ; SE P : S e p ara te )
A—4
To Next Page
Loading...