Tektronix 503, Instruction Manual

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Operating Instructions— Type 503
which bears a fixed time relationship to the input wave­
form. The following instructions show how to select and
use the proper triggering signal for various applications
of the oscilloscope.
Selecting the Trigger Source
For most applications the sweep can be triggered by the
input waveform. The only requirement is that the input
signal be large enough to provide at least 0.5 centimeter
of deflection on the screen at the sensitivity level for which
the VERTICAL SENSITIVITY control is set. To obtain trig ­
gering of the sweep from the input waveform, set the
SOURCE switch to the INT. position.
Sometimes it is advantageous to trigger the sweep with
some external signal. This is especially true when the input
waveform is of such small magnitude that it cannot provide
stable triggering of the sweep by itself. External trigger­
ing is also useful where waveforms are to be sampled from
several different places within a device. By using external
triggering, it is not necessary to reset the triggering controls
each time a new waveform is shown. In order to obtain a
stable display, it is necessary that the external waveform
bear a fixed time relationship to the input waveform. To
use an external waveform for triggering the horizontal
sweep, connect the signal to the EXTERNAL TRIG. IN con­
nector and set the SOURCE switch to the EXT. position.
When observing a waveform which bears a fixed time
relationship to the line frequency, the sweep may be trig ­
gered from the line-frequency waveform. To do this, set
the SOURCE switch in the LINE position.
Selecting the Trigger Coupling
For most recurrent waveforms, AC coupling of the trig ­
gering signal (COUPLING switch in the AC position) will
provide satisfactory triggering of the sweep. DC coupling
of the triggering signal (COUPLING switch in the DC posi­
tion) is particularly useful in triggering from random pulse
trains or very low frequency waveforms. W ith DC coupling
the sweep is triggered when the waveform reaches a preset
level (established by the Trigger LEVEL control). W ith AC
coupling the sweep is triggered when the signal reaches
a given amplitude from its average level.
Selecting the Trigger Slope
When the SLOPE switch is in the + position, the sweep
is triggered on a positive-going slope of the triggering
signal. When the SLOPE switch is in the — position, the
sweep is triggered on a negative-going slope of the trig ­
gering signal.
In most cases, selection of the triggering
slope is not critical since triggering on either slope will
provide a display which is suitable.
Selecting the Trigger Level
The LEVEL control determines the point, (AC or DC,
depending upon the setting of the COUPLING switch) on
the triggering signal at which the sweep is triggered. W ith
the SLOPE switch in the + position, adjustment of the LEVEL
control makes it possible to trigger the sweep consistently
at virtually any point on the positive-going slope o f the
triggering signal. Likewise, with the SLOPE switch in the
— position, adjustment of the LEVEL control makes it pos­
sible to trigger the sweep consistently at virtually any point
on the negative-going slope of the triggering signal. Fig.
2-6 shows the effects of the LEVEL control and the SLOPE
switch.
A t the extreme clockwise and counterclockwise ends of
its range, the LEVEL switch activates, respectively, the FREE
RUN and AUTO, switches. The effects of these switches
are discussed in the following paragraphs.
Automatic Mode of Operation
Setting the LEVEL control fully counterclockwise to the
AUTO, position sets the Type 503 Oscilloscope up for an
automatic mode of triggering which is suitable for most
applications. In this mode, the triggering signal is AC cou­
pled, and the triggering level is automatically set such that
any external triggering signal of one volt or more, or
internal triggering signal which will produce 1 centimeter
or more of deflection on the CRT screen, w ill trigger the
sweep.
In the absence of such a triggering signal, the
sweep w ill continue to be triggered automatically at about
a 50-Hz rate to produce a base line which indicates that the
instrument is adjusted to display any signal which might
be connected to the vertical channel.
Free-Running Mode of Operation
Setting the LEVEL control fully clockwise to the FREE RUN
position produces a free-running sweep, independent of
any synchronizing signal. The frequency of the free-running
sweep is dependent upon the setting of the SWEEP TIME/
CM control. This free-running trace is useful as a base line
from which to make DC measurements when the input signal
is DC coupled.
Magnification of the Sweep
Any part of the trace may be expanded horizontally
by as much as 50 times through the use of the SWEEP M A G ­
NIFIED portion of the HORIZONTAL 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 HORIZONTAL DISPLAY
switch to the desired degree of magnification.
In magnified sweep operation, the sweep rate is increased
by a factor indicated by the HORIZONTAL DISPLAY switch.
For example, if the SWEEP TIME/CM switch is set to 5 f i SEC
and the HORIZONTAL DISPLAY switch is set to X 1 0 , the
true sweep rate is 0.5 microsecond per centimeter.
NOTE
M a g n ifie d sweep rates to 0.1 m icrosecond/cm
are accurate to w ith in 5 % . C om binations o f the
SWEEP TIM E /C M and HORIZONTAL DISPLAY
switches can produce sweep rates in excess o f
0.1 m icrosecond/cm ; a t these fa ste r sweep rates,
c a lib ra tio n to le ra n ce m ay exceed 5 % .
2-6