Tektronix 543B, Instruction Manual

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Operating Instructions — Type 543B/RM543B
trigger
signal to the TRIGGER INPUT connector. External
triggering is often used when signal tracing in amplifiers,
phase-shift networks, and wave-shaping circuits. The signal
from a single point in the circuit can be used as an external
trigger signal. With this arrangement, it is possible to
observe the polarity, shaping and/or amplification of a
signal at various points through the circuit without resetting
the triggering controls for each new display.
Selecting Triggering Mode
Four means of trigger coupling are available with the
TRIGGERING MODE switch. The different coupling posi­
tions permit you to accept or reject certain frequency com­
ponents of the triggering signal.
With the switch set at AC, the time base can be triggered
with all frequency components of the triggering signal
within the trigger amplifier bandpass, including dc levels.
With the switch set at AC LF REJ, dc and low-frequency
signals (below about 17 kc) arc rejected or attenuated. Thus,
the trigger circuit will respond best to the higher-frequency
components of the triggering signal.
With the switch set to AUTO, proper triggering auto­
matically takes place providing that rhe signal waveform is
comparatively simple and approximately symmetrical. With
no trigger signal, or with a lower repetition rate, the trigger
circuit free runs at approximately 40 cps and triggers the
time base at this rate, providing a reference trace.
In general, use AC coupling. However, it will be necessary
to use DC coupling for very low-frequency signals. When
line-frequency hum is mixed with the triggering signal, it is
best to use AC LF REJ coupling so that triggering takes
place only on the signa! of interest (if the signal of interest
contains frequency components above about 17 kc).
The AC LF REJ position is also useful when triggering
internally from multitrace plug-in units operated in the
alternate dual-trace mode. AC LF REJ coupling has a faster
recovery time when subjected to the alternate dc levels
from the multitrace plug-in unit.
Selecting Trigger Slope
The TRIGGER SLOPE switch determines whether the trigger­
ing circuit responds on the rising ( + setting) or the falling
( — setting) portion of the triggering signal. When several
cycles of a signal appear in the display, the setting of the
TRIGGER SLOPE switch will probably be unimportant. How­
ever, if you wish to look at only a certain portion of a cycle,
the TRIGGER SLOPE switch will help start the display on the
desired slope of the input signal. Fig. 2-3 illustrates the
effect of both the TRIGGER SLOPE and TRIGGERING LEVEL
controls.
Setting Stability Control
In nearly all triggering applications, satisfactory opera­
tion can be obtained with the STABILITY control in the
PRESET (fully counterclockwise) position. The PRESET posi­
tion has the advantage of requiring no further adjustment of
the STABILITY control when switching from one triggering
signal to another. However, if stable triggering becomes
difficult with the STABILITY control at PRESET, it will be
necessary to adjust the control for proper triggering. To
adjust the STABILITY control, place the TRIGGERING LEVEL
control in the fully counterclockwise position, then turn the
STABILITY control slowly clockwise until a trace appears on
the crt. The correct setting is obtained by turning the control
counterclockwise three to five degrees from the point where
the trace appears.
Setting Triggering Level
The TRIGGERING LEVEL control determines the amplitude
point on the signal where triggering occurs.
The trigger circuit is most sensitive to ac triggering signals
with the TRIGGERING LEVEL control set near zero. Moving
the TRIGGERING LEVEL control in the + (plus) direction
causes the trigger circuit to respond at some higher positive
amplitude on rhe triggering signal. Moving the TRIGGERING
LEVEL control in the — (minus) direction causes the trigger
circuit to respond at some higher negative amplitude on
the triggering signal.
Selecting Time/Cm (Sweep Rate)
The TIME/CM and HORIZONTAL DISPLAY switches con­
trol sweep rate.
The TIME/CM and HORIZONTAL DISPLAY switches allow
you to view an applied signal at a wide variety of cali­
brated sweep rates. When making time measurements from
the crt, be sure the VARIABLE control is set to CALIBRATED.
When the HORIZONTAL DISPLAY switch is set to
NORMAL (X 1 ), the TIME/CM switch indicates the true
sweep rate. However, with the HORIZONTAL DISPLAY
switch set to a sweep magnified position, the setting of the
TIME/CM switch must be divided by the magnified amount
to determine the true sweep rate. For example, assume
that the TIME/CM switch is set at 1 mSEC and the HORI­
ZONTAL DISPLAY switch is set to X5. In this case, the
true sweep rate would be 1 (msec) divided by 5 (magnified
amount); resulting in a displayed sweep rate of 0.2 msec/
div. Fig. 2-4 illustrates how to make time measurements
from the graticule.
2-4