Tektronix 516 series, Instruction Manual

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Operating Instructions — Type 5 1 6
necessary to adjust the STABILITY and TRIGGERING LEVEL
controls to obtain stable triggering. In this way, the point
on the signal at which triggering will occur may be selected;
in the automatic triggering mode, triggering occurs at the
average dc level of the waveform.
The dc triggering mode, obtained by setting the red TRIG­
GER SELECTOR control in the DC position, is particularly
useful in triggering from very low-frequency waveforms.
The trigger pulses are generated when the signal reaches
a given dc level relative to ground. Suitable triggering can
be obtained from triggering signals from dc to about 5 MHz.
In the dc triggering mode, as in the ac triggering mode, it is
usually necessary to adjust the STABILITY and TRIGGERING
LEVEL controls to obtain stable triggering.
The high-frequency synchronized mode, obtained by set­
ting the red TRIGGER SELECTOR control in the HF SYNC
position, should be used to display signals from about 5 MHz
to 15 MHz. In this mode of operation, the Time-Base Trig­
ger circuit is bypassed and the triggering signal itself, either
internal or external, synchronzies the free-running opera­
tion of the Time-Base Generator. For this reason, neither
the TRIGGERING LEVEL control nor the + and — feature
of the black TRIGGER SELECTOR control I ave any effect
on the display. The sweep will always be started on a
negative-going slope of the signal. It is usually necessary
to adjust the STABILITY control to obtain a stable display.
Adjusting the STABILITY and TRIGGERING LEVEL
Controls
As mentioned previously, it is not necessary to adjust the
STABILITY and TRIGGERING LEVEL controls as long as stable
triggering can be obtained in the automatic mode of opera­
tion. However, if stable triggering cannot be obtained in the
automatic mode, it will be necessary to use one of the other
modes. In this case, it will usually be necessary to adjust
the STABILITY control or the TRIGGERING LEVEL control,
or both, to obtain a stable presentation.
Normally, in the ac and dc modes, the STABILITY control
can be set in the PRESET position, and stable triggering ob­
tained through use of the TRIGGERING LEVEL control only.
When it is not possible to obtain stable triggering with the
STABILITY control in the PRESET position, then you should
use the following procedure in adjusting the STABILITY and
TRIGGERING LEVEL controls:
1. Set both controls fully clockwise.
2. Turn the STABILITY control counterclockwise until the
trace just disappears.
3. Set the TRIGGERING LEVEL control for a stable display.
When the TRIGGERING LEVEL control is set in the -f
region of its range, triggering of the sweep will take place
at a point on the triggering signal above its average dc level.
When the TRIGGERING LEVEL control is set in the — region
of its range, triggering of the sweep will take place at a
point on the triggering signal below its average dc level.
With some signals it will be possible to obtain stable trig­
gering at several positions of the TRIGGERING LEVEL control
or throughout a considerable portion of its range. You should
set the control where it produces the most favorable display
for the purpose desired.
When the red TRIGGER SELECTOR control is in the HF
SYNC position, the TRIGGERING LEVEL control has no effect
and a stable display is obtained through the use of the STA­
BILITY control only. In this case, rotate the STABILITY con­
trol through its range until the best display is obtained on
the screen.
Setting the Sweep Rate
Throughout the operation of the oscilloscope, the TIME/
DIV. control may be adjusted at any time to present the de­
sired waveform on the crt. For most applications, the TIME/
DIV. control is set to display several cycles of a recurring
waveform. Sometimes, when it is desired to inspect some
portion of a single cycle closely, it will be best to adjust the
TRIGGERING LEVEL control so that the portion of the wave­
form to be inspected is at the extreme left-hand edge of the
graticule and then set the TIME/DIV. control to the fastest
sweep rate (smallest numercial setting) possible, still keeping
the desired portion of the waveform on the screen. The black
numbers in the inner ring around the TIME/DIV. control in­
dicate the sweep rate when the HORIZ. DISPLAY switch is
in the NORM, position.
Magnification of the Sweep
Any part of the trace may be expanded horizontally by
a factor of 5 through the use of the HORIZ. DISPLAY switch.
To expand a given portion of the sweep, first set that portion
to the center of the graticule by means of the HORIZONTAL
POSITION control. Then set the HORIZ. DISPLAY switch to
the MAG. position. The magnified sweep feature is particu­
larly useful for inspecting portions of the waveform which
cannot be expanded sufficiently and still kept on the screen
by the method described in the previous paragraph. The
small blue numbers in the outer ring around the TIME/DIV.
control give the true sweep rates when the HORIZ. DISPLAY
switch is in the MAG. position.
FREE-RUNNING OPERATION
When the STABILITY control is set fully clockwise (and
the red TRIGGER SELECTOR control is not in the AUTO,
position), the Time-Base Generator free runs to produce a
sweep independent of any synchronizing signal. The fre­
quency of the sweep can be varied from about 0.012 Hz
to 100 kHz by means of the TIME/DIV. control and the
associated VARIABLE control.
Two outputs coincident with the sweep are available at
front-panel connectors. A positive gate about 25 volts in
amplitude is available at the + GATE OUT connector, and
a positive-going sawtooth waveform, rising to a maximum
amplitude of about 150 volts, is available at the SAWTOOTH
OUT connector. Applications for free-running operation are
discussed later in this section.
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