Tektronix 434, Инструкция по эксплуатации

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O p e ra tin g In s tru c tio n s —4 3 4
fro m the betw een-channel sw itc h in g signal and b o th w ave­
fo rm s w ill be unstable. E x te rn a l trig g e rin g fro m a signal
w h ic h is tim e -re la te d to e ith e r signal provides th e same
re su lt as CH 1 trig g e rin g .
T w o signals w h ic h are tim e -re la te d can be displayed in
th e chopped m ode show ing tru e tim e re la tio n s h ip . H o w ­
ever, if the signals are n o t tim e -re la te d , the Channel 2
d isp la y w ill appear unstable.
T w o n o n -re p e titiv e , tra n s ie n t o r random signals
o cc u rrin g w ith in th e tim e interval d e te rm in e d b y the
T IM E /D IV s w itch (1 0 tim e s sweep rate) can be com pared
using th e CHOP m ode. T o trig g e r th e sweep c o rre c tly , the
Channel 1 signal m u s t precede th e Channel 2 signal. Since
th e d isp la y shows tru e tim e re la tio n s h ip , tim e -d iffe re n c e
measurem ents can be made.
A lgebraic A d d itio n
General. T he A D D p o s itio n o f th e V e rtic a l M ode s w itch
can be used to d is p la y th e sum o r d iffe re n c e o f tw o signals,
fo r co m m o n -m o d e re je c tio n to rem ove an undesired signal,
o r fo r DC o ffs e t (a p p ly in g a DC voltage to one channel to
o ffs e t th e DC c o m p o n e n t o f a signal on th e o th e r channel).
D e fle c tio n F a c to r. The overall d e fle c tio n in th e A D D
p o s itio n o f th e v e rtica l m ode s w itch w ith b o th V O L T S /D IV
sw itches set to th e same p o s itio n is th e same as the d e fle c ­
tio n fa c to r in d ica ted by e ith e r V O L T S /D IV s w itc h . The
a m p litu d e o f an added m ode d isp la y can be d e te rm in ed
d ire c tly fro m th e re s u lta n t C R T d e fle c tio n , m u ltip lie d by
th e d e fle c tio n fa c to r in dicated b y e ith e r V O L T S /D IV
sw itch . H ow ever, if the Channel 1 and 2 V O L T S /D IV
sw itches are set to d iffe re n t d e fle c tio n fa c to rs , the re s u lta n t
voltage is d if f ic u lt to d e te rm in e fro m the C RT d isp la y. In
th is case, th e voltage a m p litu d e o f the re su lta n t d isp la y can
be d e te rm in e d a c c u ra te ly o n ly if th e a m p litu d e o f the signal
applied to e ith e r channel is k n o w n .
Precautions. The fo llo w in g general p re ca u tio n s should
be observed w hen using the A D D mode.
1. D o n o t exceed th e in p u t voltage ra tin g o f the 43 4 .
2. D o n o t a p p ly signals th a t exceed an e q u iv a le n t o f
a b o u t e ig h t tim e s th e V O L T S /D IV s w itch se ttin g . For
exam ple, w ith a V O L T S /D IV sw itch se ttin g o f .5, the
voltage a pplied to th a t channel should n o t exceed a b o u t
fo u r volts. Larger voltages m ay d is to rt th e display.
3. Use Channel 1 and 2 P O S IT IO N c o n tro l settings
w h ic h m o s t nearly p o s itio n the signal o f each channel to
m id-screen w hen view ing in e ith e r the CH 1 o r CH 2 p o s i­
tio n s o f th e V e rtic a l M ode s w itc h . T h is insures the greatest
d y n a m ic range fo r A D D m ode o p e ra tio n .
4. F o r s im ila r response fro m each ch annel, set the
Channel 1 and 2 In p u t C o u p lin g sw itches to th e same
p o s itio n .
Trigger Source
C O M P . In the COMP p o s itio n o f the T R IG G E R
S O U RC E sw itc h , th e trig g e r signal is o b ta in e d fro m the
displayed signal. T h is p o s itio n provides th e m o st co n ve n ie n t
o p e ra tio n w hen d isp la yin g single channel displays. H o w ­
ever, fo r dual-trace d isp la ys, special considerations m ust be
made to p ro vid e th e c o rre c t d isp la y. See D ual-Trace O pera­
tio n in th is section fo r dual-trace trig g e rin g in fo rm a tio n .
CH 1. T h e CH 1 p o s itio n o f the T R IG G E R SO U RC E
s w itch provides a trigger signal fro m o n ly the signal applied
to th e CH 1 co n n e c to r. T h is p o s itio n provides a stable
d isp la y o f the Channel 1 signal and is useful fo r ce rta in
d ual-trace a p p lic a tio n s (see D ual-Trace O p e ra tio n ).
E X T . A n exte rn a l signal connected to the E X T T R IG
c o n n e c to r can be used to trig g e r th e sweep in th e E X T
p o s itio n o f the T R IG G E R SO U RC E s w itc h . The external
signal m u st be tim e -re la te d to the displayed signal to
pro d u ce a stable d isp la y. A n e xte rn a l trig g e r signal can be
used to p ro v id e a triggered d isp la y w hen th e in te rn a l signal
is to o lo w in a m p litu d e fo r c o rre c t trig g e rin g , o r contains
signal c o m p o n e n ts on w h ic h it is n o t desired to trig g e r. It is
also useful w h e n signal tra c in g in a m p lifie rs , phase-shift n e t­
w o rk s , wave-shaping c irc u its , etc. The signal fro m a single
p o in t in the c ir c u it can be connected to th e E X T T R IG
c o n n e c to r th ro u g h a signal p ro b e o r cable. The sweep is
th e n triggered b y th e same signal a t all tim es and allow s
e x a m in a tio n o f a m p litu d e , tim e re la tio n s h ip o r wave-shape
changes o f signals at various p o in ts in th e c ir c u it w ith o u t
resetting the T R IG G E R c o n tro ls .
Trigger C oupling
F o u r m e th o d s o f c o u p lin g th e trigger signal to the trigger
c irc u its can be selected w ith the T R IG G E R C O U P L IN G
s w itc h . Each p o s itio n p e rm its selection o r re je c tio n o f the
fre q u e n c y co m p o n e n ts o f the trig g e r signal w h ic h trig g e r
the sweep.
A C . In th e AC p o s itio n o f the T R IG G E R C O U P L IN G
s w itc h , th e DC c o m p o n e n t o f th e trig g e r signal is b lo cke d .
Signals w ith lo w -fre q u e n c y co m p o n e n ts be lo w a b o u t 20
h e rtz are a tte n u a te d . In general, A C c o u p lin g can be used
fo r m ost a p p lica tio n s. H ow ever, if the signal contains
u n w a n te d lo w -fre q u e n c y signals o r if th e sweep is to be
triggered at a lo w -re p e titio n rate or DC level, one o f the
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