Operating Information - Tektronix 1S1 Instruction Manual

No Sweep screen vertically with the DC OFFSET con-
trol.
(cont'd)
Check that the TRIGGER SENSITIVITY
control is set correctly.
Check the CONTROL TD BIAS adjustment.
Check the COMPARATOR LEVEL adjust-
ment.
Free- Check that the TRIGGER SOURCE switch
Running is not at FREE RUN.
Sweep
Check that the TRIGGER SENSITIVITY
control is set correctly.
Check the CONTROL TD BIAS adjustment.
Check the COMPARATOR LEVEL adjust-
ment.
No Check that the TRIGGER SOURCE switch
Triggering is set to the correct source and correct
slope.
Check that the input signal amplitude is
within the correct amplitude range for the
source used (40 mv to 2 volts for internal;
8 mv to 200 mv for external).
Check that the triggering signal frequency
is within the proper triggering range (100
kc to 1 Gc for sine waves). Use fast-rise
pulses from 10cps to 100kc (and up to
1 Gc).
Check that the TRIGGER SENSITIVITY and
RECOVERY TIME controls are set correctly
for the particular signal frequency.
Check the INT TRIG LEVEL adjustment.
Display Check that the triggering signal amplitude
Jitter is correct (see "No Triggering" above).
Check that the triggering signal frequency
is within the proper triggering range (see
"No Triggering"
SYNC triggering may provide a more
stable display.
Check that the triggering signal rate of
rise is fast enough (7mv/jusec or faster
for internal; 1 mv//µsec or faster for ex-
ternal).
Check that the TRIGGER SENSITIVITY and
RECOVERY TIME controls are set correctly
for the particular signal frequency.
Check the COMPARATOR LEVEL adjust-
ment.
Triggering Check that the input triggering signal am-
Cannot Be plitude is not too large for the source used
Held Off (see "No Triggering" above).
Check the INT TRIG LEVEL adjustment.

OPERATING INFORMATION

Selecting Display Dot Density
Selection of the dot density that will produce the best
display depends on both the repetition rate of the input trig-
gering signal, and the maximum repetition rate of the trigger
circuit on the time position range being used. If the input
repetition rate is low, or if the trigger holdoff period is
long, the trace progresses very slowly across the crt screen
when the dot density is high. On the other hand, if the dot
above). Above 10Mc,
Operating Instructions – Type 1S1
density is set lower than necessary, some of the display
information may be unnecessarily lost between samples. In
general, the best setting of the SAMPLES/CM control is one
that produces the highest dot density possible with a reason-
able display repetition rate. If there are fast-rise portions
on the waveform, however, it may be advantageous to set
the SAMPLES/CM control for a more dense display in order
to observe the detail of the waveform.
If smoothing is used for reducing display noise, the dot
density must be sufficiently high to allow the sampling cir-
cuits to follow the input signal closely. If the shape of
the displayed waveform changes as the SAMPLES/CM con-
trol is turned, the display is being modified by the com-
bination of smoothing and low dot density. In this case, the
control should be set for the best compromise between repeti-
tion rate and dot density that does not change the display
waveshape significantly from that present with a high dot
density.
Selecting Equivalent Sweep Rate
The various combinations of TIME/CM switch settings and
TIME POSITION RANGE indicator settings permit a consider-
able amount of flexibility in selecting the best sweep rate
and the best time positioning range for the particular wave-
form display. See "Time Magnification" below for the use
of the magnification controls.
Since the display produced by the Type 1S1 is made up of
samples taken from different cycles of the input waveform,
the sweep rate indicated by the TIME/CM switch is not the
actual display rate, but is rather the "equivalent-time" sweep
rate. This means that the TIME/CM switch is calibrated in
time units that would be appropriate if the display were a
continuous real-time presentation. This permits making ac-
curate time measurements in the sub-nanosecond range
directly from the sampling display. If the dot density is set
quite high, the actual sweep rate of the display may be very
slow, even though a very fast equivalent-time sweep rate is
used.
It is usually best to use the fastest sweep rate that is
commensurate with the waveform to be observed. This per-
mits high resolution when making time measurements, since
the portion of the waveform to be measured is spread out
over several cm. A fast sweep rate also provides the high-
est possible display repetition rate (for a given dot density),
since the holdoff period of the trigger circuit is shorter on
the time position ranges available at the faster sweep rates.
The TIME POSITION and FINE controls can then be used to
position the desired portion of the display on the screen for
observation.
If a sweep rate slower than 50µsec/cm is required, a
conventional pramplifier plug-in unit may be substituted for
the Type 1S1, or the oscilloscope and Type 1S1 can be set
for real-time sampling operation, as described later in this
section.
Time Magnification
A direct-reading time magnifier is built into the TIME/CM
switch, permitting the range of the time positioning controls
to be increased by factors of 10 and 100, and permitting up
to X100 magnification of a display from sweep rates from
50 µsec/cm to 1 nsec/cm. Horizontal dot spacing of the
display is not changed by the time magnification. This
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