Tektronix 454A User Manual

Op er at i ng
I nst r uct i ons- 454zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ‘ / R 454A
h i g h - qual i t y,
l ow- l oss cabl e . R esi st i ve
coaxi al at t enuat or s

T
h e DC Coupl i ng p osi t i o
n can be used f or
most
can b e used t o
mi ni mi ze r ef l ect i ons d ue
t o t he 15 p F i nput

ap p l i cat i ons . T h i s p osi t i on
al l ows measur eme n t of
t h e DC
ca p aci t ance
i f t he a pp l i ed si gnal
h as suf f i ci ent ampl i t u d
e .

com p one n t of ±
si gnal . I t must al so be
use d t o d i s p l ay
si gnal s bel ow a
b out 10 h er t z ( 1 h er t z wi t h
±
10
§ p r o b e) as
t h ey wi l l be
at t enuat ed i n t he AC p osi t i on .
H i g h - l evel , l ow- f r equency
si gnal s can be
connect e d
d i r ect l y t o t h
e 454 ‘ I NPU T con
n ect or s wi t h s h or t
uns h i el de d l ea
d s . T h i s cou p l i ng
met ho d wor k s best f or

I n
t h e AC Co up l i ng p
osi t i on, t he DC com p one n t of
t h e
si gnal s bel ow
a b out one k i l o h er t z
an d d ef l ect i on f act or s

si g n al i s b l oc ked by ±
capaci t or i n t h e i n p ut ci r cui t . T h
e
above o ne
vol t / di vi si on . Wh en t h i s
met ho d i s used, est abl i s
h  l ow- f r equency

r es p onse

i n t
h
e
AC posi t i on i s a b out 10
± commo
n gr oun d bet ween t
h e 454 ‘ an d t he eq ui p
ment

h er t z ( - 3 dB p oi nt ) . T
h er ef or e, some l ow- f r equency
un
d er t est ( common gr oun
d p r ovi d ed b y l i ne cor
d s i s

at t enuat i on can be ex p
ect ed near t h i s f r e q uency
l i mi t .
us u al l y i na d eq uat e) .
At t empt t o posi t i on t
h e l ea d s away

At t enuat i on i n t
he f or m of wavef or m t i l t wi l l
al so a ppear i n
f r om any so u r ce
of i n t er f er ence t o
avoi d er r or s i n t he

s q uar e waves
w h i c h have l ow- f r equency
com p onent s . T h e
di s p l ay . I f
i nt er f er ence i s excessi ve
wi t h un s h i el d ed l ea d s,

AC
cou p l i ng posi t i on p r ovi d es t h e best di s
p l ay of si gnal s
use ±
coaxi al cabl e or ± p r obe .

wi t h
±
DC
com p one nt w h i c h i s muc h
l ar ger t h an t h e AC
com p onent s .
Loadi ng E f f ect of
t he 454 ‘

T
h
e G
ND p osi t i on p r ovi d es ±
gr oun d r ef er e nce at t h e
As
near l y as

p ossi b l e,

si mul at e

act ual
oper at i ng

i n p ut
of t he 454 ‘ wi t h out t he
need t o ext er nal l y gr oun d
con
d i t i ons i n t h e eq ui p
ment un d er t est . Ot h
er wi se, t h e

t he I N PU T connect or s . T h e si g n
al a p pl i ed t o t he i n put
equi p me n t un d er t est
may n ot p r oduce ± nor mal
si g n al . T h e

connect or i s i nt er nal l y di sco nn ect e
d , b u t not gr oun d e d , an d
10 § at t e n uat or
an d f i el d ef f ect t r ansi st or
p r obes ment i one d
 t he i nput ci r cui t i s h el d at
gr oun d p ot ent i al .
p r evi ousl y
of f er t h e l east ci r cui t
l oadi ng . See t he p r o be
i nst r uct i o n manual f or l oa
d i n g ch ar act er i st i cs of t he p
r obes .

The G ND p
osi t i on can al so be used t o
p r e- c h ar ge t h e
cou p l i ng
cap aci t or t o t he aver age vol t age
l evel of t he si gnal
Wh
en
t
he si gnal i s cou p l e d di r ect l y
t o t he i n p ut of t he

a
p p
l i ed t o t h e I NPU T connect or
.
T
h i s al l ows measur ement
454 ‘ ,
t he i np ut i m p eda nce i s
about one mego h m p
ar al l el e d
 of onl y t he AC com p onent
of si g n al s h avi ng bot h AC an
d
by a b out 15 p F . Wh en
t he si gnal i s co up l e d t o
t h e i np u t

DC
com p onent s . T
h e p r e- c h ar gi ng net wor k i ncor
p or at e d i n
t h i s uni t
al l ows t h e i n p ut - cou p l i ng cap aci t or t o
c har ge t o
t hr ough ± coaxi al
cabl e, t he ef f ect i ve i nput
capaci t ance

t he DC
sour ce vol t age l evel w h en t h e I np ut Cou p
l i ng swi t c h
f r depend upon t he eque s

of t he

t y pe and l engt h of ca b
l e u se d a n d t he

i s
set t o GND . T he pr oce d u r e
f or usi ng t h i s f eat ur e i s as
ncy si gnal
.

f ol l ows :
Gr ound Consi d er at i ons

1 . B
ef or e co n nect i ng t h e si gnal co
n t ai ni ng ± DC
Gr ou
compo nent t o t he 454 ‘ I NPU T con n
ect or , set t he I n p ut
R el i abl e
si gnal measur ement s cannot be
made unl ess

Coupl i n g swi t c h t o GND . T
hen connect t he si gnal t o t h e
bot h t h
e osci l l oscope an d t he uni t un
d er t est ar e connect e d

I NPU T connect or .
t oget
h er by ± commo n r ef er ence
( gr ound) l ead i n addi t i on
t o
t he si gnal l ea d or p r obe .
Al t h oug h t h e t h r ee- wi r e AC
power cor d p r ovi des ±
common connect i on w h en use
d wi t h  2
.
W
ai t a bo u t one secon d
f or
t
he cou
p
l i ng cap aci t or t o
e q ui p ment wi t
h si mi l ar p ower cor d s, t h
e gr ou n d l oop

c h ar ge .
pr oduce d
may ma k e accur at e measur ement s
i m p ossi bl e . T he
gr oun d st r aps
sup p l i ed wi t h t h e p r o
b es p r ovi de an a d e q uat e
gr oun d .
T h e s h i el d of ± coaxi al
cabl e p r ovi d es ± common

3 .
Set t he I n p ut Cou p l i ng swi t c h t o AC .
T h e t r ace
gr ou nd w hen co nn ect ed
b et ween t wo coaxi al
connect or s

( d
i spl ay) wi l l r emai n on t he scr een an
d t h e AC com p one n t
( or wi t h sui t abl e
ada p t er s t o pr ovi de ± common
gr oun d ) .

of t h e si g n al can b e meas u r e d i n
t h e nor mal manner .
Wh en usi ng
uns
h
i el d ed si gnal l ea d s, ± commo
n gr oun d l ead
s houl d be
con nect ed f r om t he 454 ‘ c
h assi s t o t he c h assi s
of t
h
e
e q ui p ment un d er t est .

Def l ect i on F act or
Th
e amount of ver t i cal d ef l ect i o n p r o d uce d
b y ± si gnal i s
I n p ut Cou p
l i ng

det er mi
ned b y t he si g n al ampl i t ude,
t h e at t enuat i on f act or
of t h e pr obe ( i f use d ) , t
h
e
set t i ng of t he V O L TS/ DI V
Th e C h annel 1 an
d 2 I nput Coup l i ng
swi t c h es al l ow ±

swi t c h and t he
set t i ng of t he V A R I A BLE V O L
TS/ DI V
c h oi ce
of i npu t co up l i ng met
ho d s . T he t ype of di s p l ay

cont r ol . T he cal i b r at e d def l ect i on f act or s
i n d i cat e d b y t he
d esi r e d and t he a p
pl i ed si gnal wi l l det er mi n e t h
e
cou
p l i ng

V
O
L TS/ DI V swi t c hes appl y
onl y w hen t h e VA R I A BLE
t o use .

cont r ol i s set
t o t he CA L p osi t i on .
2- 1 8

Tektronix 454A Specifications

General

Brand	Tektronix
Model	454A
Category	Test Equipment
Language	English