Tektronix 502A - Page 16

Operating Instructions — Type 502A
If the trace shifts slightly between the different ranges of
the SENSITIVITY Control this may be cured by a very slight
readjustment of the DC BAL Control. The following pro 
cedure may be used to correct for this slight trace shift.
Set the free-running trace to a convenient horizontal
graticule line with the SENSITIVITY Control in the .2 VOLTS
PER CM position. Rotate the SENSITIVITY Control to the .1
mVOLTS PER CM position and bring the trace back to the
original horizontal graticule line with the DC BAL Control.
NOTE
The “ fast area" with the FINDER Button depressed
can only be easily seen on the higher sensitivity
settings of the SENSITIVITY Control.
Single Sweep
Single sweep is used to record waveforms which are not
repetitive or waveforms which jitter too much for normal
triggered-display photography.
To use the single sweep feature of the Type 502A, set
the MODE switch to NORMAL. If the waveform is repetitive
it should be connected to the input of the oscilloscope.
If the waveform is not repetitive then an AMPLITUDE CALI 
BRATOR signal of the same amplitude as that of the expected
signal should be used.
Adjust the trigger control to obtain a stable display
of the input signal. In the case of a waveform that jitters,
adjust the control to obtain the most stable display.
If a calibrator waveform was used to adjust the trigger
control, disconnect the calibrator waveform from the input
to the oscilloscope and connect the non-repetitive waveform
source to the oscilloscope. Push the MODE switch to the RE 
SET position. The READY light should now be lit. The Type
502A will now sweep once, on the first trigger received after
the MODE switch is released; further signals will not cause
the instrument to sweep.
If the waveform is repetitive leave the signal connected
to the input connector of the oscilloscope. When a sweep is
desired, push the MODE switch to RESET and let it return to
the SINGLE SWEEP position. Upon the return of the MODE
switch to the SINGLE SWEEP position, the sweep will sweep
once. If another sweep is desired the MODE switch must
again be pushed to the RESET position and returned to the
SINGLE SWEEP position.
It may be quite convenient to use the READY light of the
Single Sweep circuit as an indicator for photography. The
READY light will light when the circuit is awaiting a trigger
and will stay lit until the sweep has been completed. At the
end of the sweep the READY light will go out and stay
out until the circuit is reset for another sweep with the MODE
switch.
INTENSITY BALANCE Control
The INTENSITY BALANCE Control is used to adjust the in 
tensity of both vertical amplifiers to the same level. With
both traces adjusted to the same level, each will have
the same relative writing rate, hence each trace will show
the same amount on a photograph.
It may be necessary to readjust the INTENSITY BALANCE
Control each time the setting of the INTENSITY Control is
changed. This is due to the characteristics of a mono 
accelerator crt in which the triode characteristics for each
crt gun are slightly different.
AUXILIARY FUNCTION
AMPLITUDE CALIBRATOR
The AMPLITUDE CALIBRATOR is a source of accurately
calibrated square waves at a frequency of approximately
1 kilocycle ( + or — 30%). The output amplitude is accurate
within 3% of the AMPLITUDE CALIBRATOR switch settings
for no load conditions. The primary function of the calibrator
is to provide a convenient method for checking the calibra 
tion of the vertical-deflection system and for adjusting the
probes. It can be used for other purposes, however, if
it is kept in mind that the output impedance of the cali 
brator varies with the output-voltage setting.
Trace-brightness (intensity) modulation
To couple markers or other signals into the crt cathodes
for trace-brightness modulation, disconnect the ground strap
at the rear of the instrument and apply the signal between
the CRT CATHODE binding post and GND . This will simultan 
eously apply the signals to the upper and lower beam
cathodes. At normal brightness, positive signals of about 25
volts will cut the beams off. Always replace the ground strap
when you are not intensity modulating the beams.
Graticule illumination
The graticule lighting control, labeled POWER AND SCALE
ILLUM, can be ad|usted to suit the lighting conditions of
the room. A light filter is supplied with the instrument
which can be used for increased contrast. This filter should
be mounted next to the crt face so it does not block the light
from the graticule lines.
The graticule of the Type 502A Oscilloscope can be
illuminated so' that it appears to have either red or white
graticule markings. The markings can be quickly changed
from white to red or from red to white by removing the
graticule cover and inverting the graticule. As a general
rule, white graticule lines are superior to red for photo 
graphic purposes.
Direct connection to crt plates
In some applications, it may be desirable to connect a
signal directly to one or more sets of crt deflection
plates — bypassing the internal oscilloscope amplifiers. This
can be done in the Type 502A if certain precautions are
observed. One of these precautions is to m a intain the aver 
age d c voltage on the deflection plates at approximotely
+225 volts. If the average voltage is not maintained at
approximately +225 volts, the crt display may be defocused.
For many applications, ac coupling of the signal to the
deflection plates is permissible. It has the advantage of
allowing the use of front panel controls to position the
display and permits the use of signals not having the re 
quired average voltage level. A diagram of this method of
2-10
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