Tektronix 551 Dual Beam Instruction Manual page 10

Now reset the HORIZONTAL DISPLAY switch to the
NORMAL position.
Effect of the Trigger Slope Switch
Carefully observe that part of the display which appears
at the left-hand end of the graticule. Notice that the trace
begins during the rising portions of the square waves. That
is, the sweep is triggered at a time when the slope of the
wave is positive (see Fig. 2-1). This is because the black
TRIGGER SLOPE knob is set at + UPPER rather than at
—UPPER.
Fig. 2-1. The setting of the TRIGGER
whether the display will start during the rise ( +
( — slope) of the triggering waveform.
Now turn the TRIGGER SLOPE knob to —UPPER. Observe
that both traces appear to turn upside down, so that they
now begin during the falling portion of the square wave, at
the left-hand end of the graticule. That is, the sweep is
triggered at a time when the slope of the wave is negative.
Note that one of the purposes of the TRIGGER SLOPE switch
is to provide control over whether the sweep is triggered
when the slope of the waveform is positive, or whether the
sweep is triggered when the slope of the waveform is
negative.
Now turn the TRIGGER SLOPE switch to —LOWER. Ob­
serve that the display has the same appearance that it had
when the TRIGGER SLOPE switch was in the —UPPER posi­
tion. This is because the sweep is triggered when the slope
of the square wave is negative, as was the case when the
TRIGGER SLOPE switch was in the —UPPER position. Now
turn the TRIGGER SLOPE switch to the + LOWER position.
Notice that the display has the same appearance in the
+ LOWER and +UPPER positions of the TRIGGER SLOPE
switch.
Further use of the TRIGGER SLOPE knob will be described
in the Operating Instructions under the heading " Horizontal
Deflection System".
Now return the TRIGGER SLOPE knob to the + UPPER
position.
® ®
SLOPE switch determines
slope) or fall
The AC Triggering Mode
Check that the TRIGGER SLOPE switch is set at -(-UPPER,
that the TRIGGERING LEVEL control is turned full right or
full left, and that the STABILITY control is at PRESET. Turn
the red TRIGGERING MODE switch to AC. The trace should
now disapper from the screen.
Slowly turn the TRIGGERING LEVEL control toward the
center of its range until the trace reappears; adjust this
control for a stable display of the two waveforms. Trigger­
ing is now being effected in the AC mode.
Remove the SQUARE-WAVE CALIBRATOR lead from the
INPUT A connector of the UPPER BEAM plug-in. Note that
this causes the display to disappear. Now reconnect the
SQUARE-WAVE CALIBRATOR lead to the INPUT A connec­
tor of the UPPER BEAM plug-in so that the display reappears.
Remove the SQUARE-WAVE CALIBRATOR lead from the
INPUT A connector of the LOWER BEAM plug-in. Note that
the square-wave display of the lower beam is replaced by
a horizontal reference trace, while the upper beam display is
unaffected. This is because the sweep is triggered from the
waveform displayed by the UPPER BEAM.
Now reconnect the SQUARE-WAVE CALIBRATOR lead to
the INPUT A connector of the LOWER BEAM plug-in.
Slowly turn the TRIGGERING LEVEL control several times
back and forth throughout its range from —, through + .
Carefully observe the left-hand end of the display while you
do this. Note that there is a certain part of the range of
this control that provides a display; settings too far toward
the — or + marks on the panel result in no display.
Also notice that, in that part of the range of the TRIG­
GERING LEVEL control where you get a display, this control
determines the height or " level" of the point on the wave­
form where the trace starts. If you set this control more
toward the + part of its range, the display starts higher on
the waveform (see Fig. 2-2). Since the TRIGGER SLOPE knob
is set at +UPPER, the display in each case starts on the
rising part of the waveform (where the slope is positive).
Next, set the VOLTS/CM control on the UPPER BEAM plug­
in to 10. The display will now be smaller and may disap­
pear from the screen. If the display does disappear, turn the
TRIGGERING LEVEL control towards its mid-range position
(indicated by the 0 on the front panel). By carefully ad-
STABILITY
Fig. 2-2. With the TRIGGER SLOPE switch at + UPPER in the AC
triggering mode, the TRIGGERING
point on the rising part of the UPPER-BEAM waveform at which
the display will start.
Getting Acquainted— Type 551
LEVEL control determines the
2-3