Tektronix 511A-AD, Instruction Manual, Page: 10 / 75

NOTE — When using the internal trigger im-
pulses to view fundamental frequencies
above about 2mc it will be necessary to
progressively advance the SWEEP STA­
BILITY control somewhat above the normal
operating point to secure a stable pattern.
Function of Trigger Sei.
This control selects the trigger impulse to be used
from three sources, the line frequency, (60 cycles), the
video amplifier ( +INT and — INT), or the TRIGGER IN ­
PUT binding post. Two positions are available for both
the INT. and EXT. sources. When using those marked
4- the sweep starts at the rising portion of the trigger
impulse. The — positions start the sweep on the falling
portion. When the INPUT CHAN. SEL. switch is in the
2 STAGES position the + INT and — INT positions are
reversed in polarity since the trigger impulses are shifted
180 º by the pre-amplifier stage. For satisfactory opera­
tion in the EXT. positions a trigger of from 1 V to 50 V
peaks should be provided. Larger triggers should be
reduced by an external attenuator.
Adjustment of Trigger Ampl.
The TRIGGER AMPL. control adjusts the bias in the
trigger amplifier and therefore the amplitude of the
impulse which reaches the multivibrator. After the
SWEEP STABILITY is set as described previously, and
the TRIGGER SEL. switch set to the correct position, ad­
vance the TRIGGER AMPL. control until a stable image
is obtained. When the trigger source is a slowly chang ­
ing wave such as a sine wave or sawtooth, adjustment
of the TRIGGER AMPL. setting will change the phase
of the signal relative to the start of the sweep.
In general, it is desirable to use the minimum TRIG ­
GER AMPL. setting required to insure a stable image.
If poor synchronizing is experienced when the Type
511 -A is used to observe repetitive signals containing
erratic peak voltages, such as produced by vibrating
contacts, it may be possible to form a stabilized trigger
signal by the use of auxiliary limiting and differentiat­
ing circuits. The TRIGGER SEL. switch should then be
set to the proper EXT. polarity, and connection made to
the TRIGGER INPUT.
Adjustment of Sweep Speed
The combination of SWEEP RANGE and SWEEP
SPEED MULT, controls allows the operator to vary the
sweep speed so that the marked portion of the grati ­
cule (10 cm) is covered by the trace in any time from
.1 sec. to 1 microsecond. The number of microseconds
required for the sweep to traverse the 10 cm. scale is
determined by multiplying the SWEEP RANGE reading
by the sum of the readings of the SWEEP SPEED MULT,
dials. This indicated reading is accurate within 5%
when calibrated at the factory. Provision has been
made to compensate for variations caused by different
tubes, etc., by a screwdriver adjustment inside the case.
Procedure for adjustment of this control is described in
Section IV.
Recurrent Sweep
In case it is desirable to have a sweep without using
any sort of trigger, merely advance the SWEEP STABILI ­
TY control until a stable sweep is obtained. This sweep
is the
conventional
sawtooth variety
as used
in
most
oscilloscopes.
Single Sweep
The triggered sweep circuit used in the Type 511 in ­
herently provides for single sweep operation. The beam
is blanked out until the trigger simultaneously turns it
on and starts the sweep. For single sweep operation a
mechanical contact or hand key can be connected be ­
tween the TRIGGER INPUT binding post and ground.
If repeated sweeps occur due to intermittent or bouncing
contact, a capacitor of .1 mf. to 1 mf. should be con ­
nected across the contact. This capacitor is charged
through 22 megohms and the long time constant pre ­
vents an immediate recurrence of the sweep.
Sweep Magnifier
Frequently it is desirable to examine in some detail
a portion
of the
waveshape
under observation,
for
in­
stance the rate of fall of the end of a fairly long pulse.
In the Type 511-A the sweep magnifier circuit makes it
possible to expand any desired 20% of the sweep to
cover the entire tube face. When the SWEEP MAGNI ­
FIER POSITION control is moved from the OUT position,
the sweep is delayed for a variable time and then goes
at about 5 times its normal rate. The operating pro ­
cedure is to turn the SWEEP MAGNIFIER POSITION to
OUT. Adjust the sweep speed controls so that the por ­
tion of the wave to be magnified is at the right side of
the tube. Now turn the SWEEP MAGNIFIER POSITION
knob clockwise until the desired signal moves in from
the right to the center of the tube face. The magnified
sweep is not linear over its entire trace so that it is de­
sirable to use only the center two inches if possible. If
higher magnification than five is wanted it is only neces­
sary to
change
R47 to
a
larger
value.
A value of
10
K
will give a magnification of about 10. The somewhat
lower value chosen appears to be a more usable value
in most cases.
NOTE —A sweep of 10 cm per microsecond
is about the limit of the sweep amplifiers,
so that care must be taken that the magni­
fied sweep does not exceed this value.
Ext. Sweep Input
Provision has been made for the connection of ex­
ternal
sweep
generators
to the Type 511A. This
might
be a sine wave oscillator for frequency comparison, the
sweep obtained from a "Frequency sweep" signal gen­
erator, etc., or an auxiliary slow sweep generator. The
EXT. SWEEP INPUT binding post is connected to the
horizontal deflection plates via the EXT. SWEEP ATTEN.
and a one stage push pull amplifier. The entire system
is DC coupled, permitting the use of very slow sweeps.
TYPE 511-A, 511-AD SECTION 2, PAGE 2