Trigger Slope; Trigger Level; Horizontal Sweep Rates; Time Measurement - Tektronix 7B80 Instruction Manual

Operating Instructions-7B80
EXTERNAL. The EXT position connects the signal from
the EXT TRIG IN connector to the trigger circuit. The ex-
ternal signal must be time-related to the displayed wave-
form for a stable display. An external trigger signal can be
used t o provide a triggered display when the internal signal
is either too low in amplitude for correct triggering or con-
tains signal components on which triggering is not desired.
It is also useful when signal tracing in amplifiers, phase-shift
networks, wave-shaping circuits, etc. The signal from a
single point in the circuit can be connected to the EXT
TRIG IN connector through a probe or cable. The sweep is
then triggered by the same signal at all times and allows am-
plitude, time relationship, or waveshape changes of signals
at various points in the circuit to be examined without re-
setting the TRIGGERING controls.
The +10 push button attenuates the external trigger signal
by a factor of 10. Attenuation of high amplitude external
trigger signals is desirable to increase the effective range of
the LEVEL control.
Trigger Slope
The TRIGGERING SLOPE switch (concentric with the
TRIGGERING LEVEL control) determines whether the
trigger circuit responds on the positive- or negative-going
portion of the trigger signal. When the SLOPE switch is in
the (+) (positive-going) position, the display starts on the
positive-going portion of the waveform (see Figure 1-3).
When several cycles of a signal appear in the display, the
setting of the SLOPE switch is often unimportant. How-
ever, if only a certain portion of a cycle i s to be displayed,
correct setting of the SLOPE switch is important to provide
a display that starts on the desired slope of the input signal.
Trigger Level
The TRIGGERING LEVEL control determines the voltage
level on the trigger signal at which the sweep is triggered.
When the LEVEL control is set in the
+
region, the trigger
circuit responds at a more positive point on the trigger sig-
nal. When the LEVEL control is set in the - region, the
trigger circuit responds at a more negative point on the
trigger signal. Figure 1-3 illustrates this effect with different
settings of the SLOPE switch.
To set the LEVEL control, first select the TRIGGERING
MODE, COUPLING, SOURCE, and SLOPE. Then set the
LEVEL control fully counterclockwise and rotate it clock-
wise until the display starts at the desired point.
Horizontal Sweep Rates
The TIMEIDIV switch provides calibrated sweep rates from
5 seconds/division to 10 nanoseconds/division in a 1-2-5
sequence. The VARIABLE TIMEIDIV control must be in
the calibrated position and the MAG switch set to X I to
obtain the sweep rate indicated by the TIMEIDIV switch.
However, the mainframe crt readout will display the appro-
priate sweep rate.
The VARIABLE TIMEIDIV control includes a two-position
switch to determine if the sweep rate i s calibrated, or un-
calibrated. When the VARIABLE control is pressed in, it is
inoperative and the sweep rate i s calibrated. When pressed
and released outward, the VARIABLE control i s activated
for uncalibrated sweep rates, to at least the sweep rate of
the next slower position.
A calibrated sweep rate can be obtained in any position of
the VARIABLE control by pressing in the VARIABLE con-
trol. This feature is particularly useful when a specific un-
calibrated sweep rate has been obtained and it is desired to
switch between calibrated and uncalibrated displays.
Time Measurement
When making time measurements from the graticule, the
area between the second and tenth vertical lines of the gra-
ticule provides the most linear time measurements (see
Figure 1-4). Position the start of the timing area to the
second vertical line and adjust the TIMEIDIV switch so the
end of the timing area falls between the second and tenth
vertical lines.
Sweep Magnification
The sweep magnifier can be used to expand the display by a
factor of 10. The center division of the unmagnified display
is the portion visible on the crt in the magnified form (see
Figure 1-5). The equivalent length of the magnified sweep is
more than 100 divisions; any 10 division portion can be
viewed by adjusting the POSITION and FINE POSITION
controls to bring the desired portion into the viewing area.
When the MAG switch is set t o X I 0 (OUT) the equivalent
magnified sweep rate can be determined by dividing the
TIMEIDIV setting by 10; the equivalent magnified sweep
rate is displayed on the crt readout.
Variable Hold Off
The HOLD OFF control improves triggering stability on re-
petitive complex waveforms by effectively changing the
repetition rate of the horizontal sweep signal. The HOLD
OFF control should normally be set to i t s minimum setting.
When a stable display cannot be obtained with the TRIG-
GERING LEVEL control, the HOLD OFF control can be
varied for an improved display. If a stable display cannot be
obtained at any setting of the LEVEL and HOLD OFF con-
trols, check the TRIGGERING COUPLING and SOURCE
switch settings.
Scans by ArtekMedia O 2006