General Operating Information; Triggering Switch Logic; Triggering Modes - Tektronix 7B80 Instruction Manual

Operating Instructions-7B80
8. Press the AC COUPLING, INT SOURCE, and NORM
MODE buttons. Adjust the LEVEL control for a stable
display.
9. Press the AUTO MODE button and adjust the LEVEL
control for a free-running display.
10. Press the NORM MODE button and check for no
display.
11. Adjust the LEVEL control for a stable display and
press the SINGLE SWP MODE button.
12. Note that one trace occurs when the RESET MODE
button is pressed.
13. Disconnect the mainframe calibrator signal from the
amplifier unit input and press the RESET MODE button.
Check for no display and note that the READY indicator
is lit.
14. Note that one trace occurs and that the READY indi-
cator extinguishes when the mainframe calibrator signal is
reconnected t o the amplifier unit input.
GENERAL OPERATING INFORMATION
Triggering Switch Logic
The MODE, COUPLING, and SOURCE push buttons of the
TRIGGERING switches are arranged in a sequence which
places the most-often used position at the top of each series
of push buttons. With this arrangement, a stable display can
usually be obtained by pressing the top push buttons: P-P
AUTO, AC, INT. When an adequate trigger signal is applied
and the LEVEL control is correctly set, the unit is triggered
a s indicated by the illuminated TRIG'D light. If the
TRIG'D light is not on, the LEVEL control is either at a
setting outside the range of the trigger signal applied t o this
unit from the vertical unit, the trigger signal amplitude i s in-
adequate, or its frequency is below the lower frequency
limit of the AC COUPLING switch position. If the desired
display is not obtained with these buttons pushed in, other
selections must be made. Refer t o the following discussions
or the instruction manuals for the associated oscilloscope
mainframe and vertical unit(s) for more information.
Triggering Modes
The MODE push-button switches select the mode in which
the sweep is triggered.
P-P AUTO. The P-P AUTO MODE provides
a
triggered dis-
play at any setting of the LEVEL control whenever an ade-
quate trigger signal
i s
applied. The range of the LEVEL
control in the P-P AUTO MODE
i s
between approximately
10% and 90% of the peak-to-peak amplitude of the trigger
signal. The LEVEL control can be set so that the displayed
waveform starts
a t
any point within this range on either
slope. The trigger circuits automatically compensate for a
change in trigger-signal amplitude. Therefore, i f the LEVEL
control i s set t o start the waveform display at a certain per-
centage point on the leading edge of a low-amplitude signal,
it triggers at the same percentage point on the leading edge
of a high-amplitude signal if the LEVEL control is not
changed. When the trigger repetition rate is outside the
parameter given in the Specification section, or when the
trigger signal is inadequate, the sweep free runs at the rate
indicated by the TIME/DIV switch t o produce a bright
base-line reference trace (TRIG'D light off). When an ade-
quate trigger signal i s again applied, the free-running condi-
tion ends and a triggered display is presented.
The P-P AUTO MODE is particu!arly useful when observing
a series of waveforms, since it is not necessary t o reset the
LEVEL control for each observation. The P-P AUTO
MODE is used for most applications because of the ease of
obtaining a triggered display. The AUTO, NORM, and
SINGLE-SWP MODE settings may be used for special
applications.
AUTO. The AUTO MODE provides a triggered display
with the correct setting of the LEVEL control whenever an
adequate trigger signal i s applied (see Trigger Level discus-
sions). The TRIG'D light indicates when the display is
triggered.
When the trigger repetition rate is outside the frequency
range selected by the COUPLING switch or the trigger sig-
nal is inadequate, the sweep free runs at the rate indicated
by the TIME/DIV switch (TRIG'D indicator off). An ade-
quate trigger signal ends the free-running condition and a
triggered display is presented. The sweep also free runs at
the rate indicated by the TIMEIDIV switch when the
LEVEL control is at a setting outside the amplitude range
of the trigger signal. This type of free-running display is
useful when it i s desired t o measure only the peak-to-peak
amplitude of a signal without observing the waveshape
(such as bandwidth measurements).
NORMAL. The NORM MODE provides a triggered display
with the correct setting of the LEVEL control whenever an
adequate trigger signal is applied. The TRIG'D light indi-
cates when the display is triggered.
Scans by ArtekMedia O 2006