Operating Instructions—434
from the between-channel switching signal and both wave
form s w ill be unstable. External triggering from a signal
which is time-related to either signal provides the same
result as CH 1 triggering.
Tw o signals which are tim e-related can be displayed in
the chopped mode showing true time relationship. H ow
ever, if the signals are not time-related, the Channel 2
display w ill appear unstable.
Two non-repetitive, transient or random signals
occurring w ith in the tim e interval determined by the
T IM E /D IV switch (10 times sweep rate) can be compared
using the CHOP mode. To trigger the sweep correctly, the
Channel 1 signal m ust precede the Channel 2 signal. Since
the display shows true tim e relationship, tim e-difference
measurements can be made.
Algebraic Addition
General. The A D D position o f the Vertical Mode switch
can be used to display the sum or difference o f tw o signals,
fo r comm on-mode rejection to remove an undesired signal,
or fo r DC offset (applying a DC voltage to one channel to
offset the DC com ponent o f a signal on the other channel).
Deflection Factor. The overall deflection in the ADD
position of the vertical mode switch w ith both V O LT S /D IV
switches set to the same position is the same as the deflec
tion factor indicated by either V O LTS /D IV switch. The
am plitude of an added mode display can be determined
directly from the resultant CRT deflection, m ultiplied by
the deflection factor indicated by either V O L TS /D IV
switch. However, if the Channel 1 and 2 V O LT S /D IV
switches are set to different deflection factors, the resultant
voltage is d iffic u lt to determine from the CRT display. In
this case, the voltage amplitude of the resultant display can
be determined accurately only if the amplitude of the signal
applied to either channel is known.
Precautions. The fo llow ing general precautions should
be observed when using the ADD mode.
1. Do not exceed the input voltage rating o f the 434.
2. Do not apply signals th at exceed an equivalent of
about eight times the V O LT S /D IV switch setting. For
example, w ith a V O LTS /D IV switch setting of .5, the
voltage applied to that channel should not exceed about
fo ur volts. Larger voltages may d istort the display.
3. Use Channel 1 and 2 POSITION control settings
which m ost nearly position the signal of each channel to
mid-screen when viewing in either the CH 1 or CH 2 posi
tions of the Vertical Mode switch. This insures the greatest
dynam ic range fo r AD D mode operation.
4. For similar response from each channel, set the
Channel 1 and 2 Inp ut Coupling switches to the same
position.
Trigger Source
C O M P . In the COMP position of the TRIGGER
SOURCE switch, the trigger signal is obtained from the
displayed signal. This position provides the most convenient
operation when displaying single channel displays. How
ever, fo r dual-trace displays, special considerations must be
made to provide the correct display. See Dual-Trace Opera
tio n in this section fo r dual-trace triggering inform ation.
CH 1. The CH 1 position of the TR IG G ER SOURCE
switch provides a trigger signal from only the signal applied
to the CH 1 connector. This position provides a stable
display o f the Channel 1 signal and is useful fo r certain
dual-trace applications (see Dual-Trace O peration).
EXT. An external signal connected to the EXT TRIG
connector can be used to trigger the sweep in the EXT
position of the TRIGG ER SOURCE switch. The external
signal must be time-related to the displayed signal to
produce a stable display. An external trigger signal can be
used to provide a triggered display when the internal signal
is too low in amplitude fo r correct triggering, or contains
signal components on which it is not desired to trigger. It is
also useful when signal tracing in amplifiers, phase-shift net
works, wave-shaping circuits, etc. The signal from a single
point in the circu it can be connected to the EXT TRIG
connector through a signal probe or cable. The sweep is
then triggered by the same signal at all times and allows
examination of amplitude, tim e relationship or wave-shape
changes of signals at various points in the circu it w ith out
resetting the TRIG GER controls.
Trigger Coupling
Four m ethods o f coupling the trigger signal to the trigger
circuits can be selected w ith the TRIGG ER COUPLING
switch. Each position permits selection or rejection o f the
frequency components of the trigger signal which trigger
the sweep.
AC. In the AC position of the TRIG GER COUPLING
switch, the DC com ponent of the trigger signal is blocked.
Signals w ith low-frequency components below about 20
hertz are attenuated. In general, AC coupling can be used
fo r most applications. However, if the signal contains
unwanted low-frequency signals or if the sweep is to be
triggered at a low -repetition rate or DC level, one o f the
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