Tektronix 502 series, Инструкция по эксплуатации

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TRIGGERED OPERATION
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In order to obtain a stable display of some
recurrent waveform, it will be necessary for you
to trigger the horizontal sweep at the correct in­
stant of time. This will insure that the sweep will
start at the same point on the observed wave­
form for each cycle of operation. The sweep
should be triggered either by some waveform
bearing a fixed time relationship to the observed
waveform or by the observed waveform itself.
Either method will produce the desired stable
display. If the waveform which is applied to the
upper beam and the waveform which is applied
to the lower beam have a definite time relation­
ship to each other it is possible to trigger from
either beam and obtain simultaneously a stable
display of both waveforms.
The following instructions tell you how to
select the proper triggering signal for various
applications of your oscilloscope. These instruc­
tions also provide information about the advan­
tages and limitations of each triggering mode.
You should attempt to become thoroughly fa­
miliar with all of the various triggering modes in
order that you may obtain maximum use from
your instrument. A thorough knowledge of the
triggering modes will allow you a greater selec­
tion of triggering methods when you are con­
fronted with a definite triggering problem.
How to select the triggering signal source.
1. To trigger the sweep from the waveform dis­
played on the upper beam, set the TRIGGER
SELECTOR switch at UPPER AC or UPPER DC.
2. To trigger the sweep from the waveform dis­
played on the lower beam, set the TRIGGER
SELECTOR switch at LOWER AC or LOWER DC.
3. To trigger the sweep at the power line fre­
quency, set the TRIGGER SELECTOR switch at
LINE. You would normally use this mode of trig­
gering when you are observing a waveform
which bears a fixed time relationship to the
power-line frequency.
4. To trigger the sweep from some external
waveform bearing a definite time relationship to
the observed waveform, connect the external
waveform to the TRIGGER INPUT connector and
set the TRIGGER SELECTOR switch at EXT AC or
EXT DC. External triggering provides definite
advantages over other modes of triggering in
certain cases. With external triggering, the trig ­
gering signal generally remains essentially con­
stant in amplitude and shape. It is thereby
possible to observe the shaping and amplifica­
tion of a signal by each stage of a circuit with­
out resetting the triggering controls for each
observation. Also time and phase relationships
between the waveforms at different points in the
circuit can be seen. If, for example, the external
triggering signal is derived from the waveform
at the input to a circuit, the time relationship
and phase of the waveforms at each point in the
circuit are automatically compared to the input
signal by the display presented on the face of
the crt.
How to select the triggering mode.
Automatic Mode
Automatic triggering is obtained by rotating
the TRIGGERING LEVEL control fully counter­
clockwise to the AUTOMATIC position. This
mode provides a preset triggering level which is
set to allow triggering at the average voltage
point of the applied waveform. Also, the sweep
runs at approximately a 50 cycle rate when no
triggering signals are applied. Automatic trig­
gering can be used with triggering signals ob­
tained from the LINE, UPPER, LOWER, or EXT
positions of the TRIGGER SELECTOR switch, but
for most waveforms, it is useful only for trigger­
ing at frequencies above approximately 50
cycles. Automatic triggering saves considerable
time in observing a series of waveforms since
it is not necessary to reset the triggering level
for each observation. For this reason, it is the
mode that is normally used. Other modes are
normally used only for special applications or
where stable triggering is not attainable in the
automatic mode.
DC Mode
The dc mode is selected in the UPPER DC,
LOWER DC, and EXT DC positions of the TRIG­
GER SELECTOR switch. This mode of triggering
is particularly useful in triggering from wave­
forms which are not adaptable to the ac mode,
such as random pulse trains or very low fre­
quency waveforms. Random pulse trains pose a
special problem in the ac mode since the ran­
dom occurance of the input waveforms causes
the average voltage level to shift. This in turn
may cause the triggering level to shift to an un­
stable point. This problem is not encountered in
the dc mode since the triggering point is deter­
mined only by instantaneous voltages.
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OPERATING INSTRUCTIONS — TYPE 502
3-3