Tektronix 455, Instruction Manual, Page: 32 / 246

Operating Instructions—455/A2/B2
37
A TRIGGER L E V E L—Selects the amplitude point on
the trigger signal at which the sweep is triggered. It is
usually adjusted fo r the desired display after trigger
SOURCE, COUPLING, and SLOPE have been selected.
3 8
SOURCE—Determines the source of the trigger signal
coupled to the input of the trigger circuit.
3 9
COUPLING—Determines the method used to couple
signals to the trigger generator circuit.
AC: Signals are capacitively coupled to the input
of the trigger generator. Dc is rejected and signals
below about 60 Hz are attenuated.
NORM: The trigger signal is obtained from the
signal(s) displayed on the crt. Does not show the
time-relationship o f the channel 1 and channel 2
signals in the alternate vertical mode. The NORM
setting is not recommended fo r use w ith the
CHOPPED vertical mode because the display
triggers on the switching transients.
CH 1: A sample o f the signal present in the chan­
nel 1 preamplifier is used as a trigger signal. The
channel 2 display can be unstable if it is not time-
related to the channel 1 signal.
LF REJ: Signals are capacitively coupled to the
input o f the trigger circuit. Dc is rejected and sig­
nals below about 50 kHz are attenuated. It is use­
fu l fo r providing a stable display o f the high-frequen­
cy components o f a complex waveform.
HF REJ: Signals are capacitively coupled to the
input of the trigger circuit. Dc is rejected and sig­
nals below about 60 Hz and above 50 kHz are
attenuated. It is useful fo r providing a stable dis­
play o f the low-frequency components o f a com­
plex waveform.
CH 2: A sample o f the signal present in the chan­
nel 2 preamplifier is used as a trigger signal. The
channel 1 display can be unstable if it is not time-
related to the channel 2 signal.
LINE (A Trigger circuit only): A sample of the
power-line frequency is used as a trigger signal. It
is useful when the input signal is time-related (mul­
tiple or sub-multiple) to the line frequency or when
it is desirable to provide a stable display of a line-
frequency component in a complex waveform.
DC: A ll components o f a trigger signal are coupled
to the input o f the trigger circuit. It is useful fo r
providing a stable display o f low-frequency or low-
repetition rate signals.
4 0
POWER—Turns instrument power on (out) and o ff
(in).
EXT: Signals connected to the External Trigger
Input connectors are used fo r triggering. External
trigger signals must be time-related to the displayed
signal fo r a stable display. It is useful when the in­
ternal signal is too small or contains undesired
signals that could cause unstable triggering. It is
also useful when operating in the chopped mode.
EXT -f- 10 (A Trigger circuit only): External trig ­
ger signal attenuated by a factor o f 10.
STARTS AFTER D E LA Y (B Trigger circu it only):
B sweep runs immediately after the delay tim e se­
lected by the A T IM E /D IV switch and the D E LA Y
TIM E POS control. No B trigger is required. In any
other B SOURCE switch position, a trigger is re­
quired after the delay time before B sweep w ill run.
41
A and B T IM E /D IV -T h e A T IM E /D IV switch (clear
plastic skirt) selects the sweep rate fo r the A sweep
generator circuit and selects the basic delay tim e fo r
delayed sweep operation. M ultiply the A T IM E /D IV
switch setting by the D E LA Y TIM E POS control to
compute the delay time. The VA R control must be
in the detent position fo r calibrated A sweep rate and
delay times.
The B T IM E /D IV switch (grey knob, pull out and turn
to unlock) selects the B sweep rate fo r delayed sweep
operation.
When A T IM E /D IV switch is fu lly counterclockwise
(X-Y position), horizontal deflection is provided by
the signal connected to the vertical CH 1 input
connector.
REV. A. O C T 1975
2-7