Tektronix 549 Instruction Manual page 10

OPERATING INSTRUCTIONS
Introduction
The Type 549 combines high speed storage with a general
purpose laboratory oscilloscope. Th is section of the manual
describes operation and applications of the instrument.
The description begins with the storage tube and its oper­
ational characteristics, then covers each front and rear panel
control, switch and connector.
Circuit functions and modes of operation for the Type 549
are described next, with emphasis on storage and storage
technique. -
The section concludes with general oscilloscope measure­
ment applications.
Storage Tubes
Terms and storage nomenclature used in this manual are
defined at the start of the circuit description section.
brief discussion on storage tube principles is also presented.
The storage tube in the Type 549 is a relatively new tube,
and can be more easily damaged than conventional CRT's.
However with reasonable care they w ill provide very satis­
factory servise. The following precautions w ill prevent dam­
age, increase tube life and maintain optimum performance.
Protective circuitry is incorporated to lim it beam inten­
sity. However, a repetitive sweep over the same area for
extended periods may damage the storage target. Use only
the intensity level required to write a well-defined display.
Turn the IN T E N S IT Y control to its minimum setting during
warm-up time and before changing to slower sweep speeds
or switching the H O R IZO N TA L DISPLAY selector.
Turn the IN T E N S IT Y control
POW ER switch to OFF when changing plug-in units.
Avoid continued use of one target area. Th is causes dif­
ferential aging of the storage target and may result in d if­
ferential light emitting qualities over the target area.
Avoid leaving stored display on the screen longer than
required. Operation in the ready-to-write
state w ill give longer target life.
When store operation is no longer required, shift to con­
ventional mode operation. Conventional operation does not
deteriorate the storage screens; however, avoid prolonged
display periods of a repetitive waveform or a free running
sweep. These may cause a residual image of the display to
appear in the store mode.
Readjustment of the focus and astigmatism
required after the beam intensity level is changed to main­
tain optimum writing speed.
Storage tube characteristics change with use more notice­
ably than characteristics of conventional tubes. Circuit cali­
bration should, therefore, be checked frequently to ensure
optimum operation. Operating levels for a new tube should
be checked after the first 100 hours of operation. Progres­
@2
SECTION 2
A
counterclockwise and the
(fully erased)
is usually
sively longer periods between checks may then be set.
Storage Target Phenomena
The storage screen may display unusual dark or bright
areas which resemble previously written information. Three
different types of residual images may be noted.
1. Negative resid ual image.
Th is appears in the ready-to-write state as a negative
image of some previously stored display.
leaving a stored display on the target over an extended
period. Th is type of image usually disappears within a few
hours of operation.
2. Brig h t resid ual image.
Th is appears only in the enhanced mode as a bright image
of some previously written display. The secondary emission
characteristics of the affected target area have changed so
that they fade positive when pulsed by the enhanced pulse
while the reminder of the target area reacts normally.
These bright residual images are caused by stored dis­
plays for extended periods. They are not a problem if the
enhance level is kept below the point the images appear and
with time w ill fade away.
3. D ark Burn.
Th is is a spot or line across the screen which has a lower
light level than the rest of the target when the target is
fu lly written. If extreme, the dark burn area w ill not store.
Dark burn is caused by the destruction of the storage
screen from a high intensity writing beam and is sim ilar to
phosphor burn in a conventional CRT.
Th is type of damage may remain indefinitely if the burn
is extensive.
Generally, non-destructive type images w ill fade in about
the same period of time it took to produce them. It is import­
ant to age the target area as uniformly as possible to main­
tain uniformity in writing speed and light level.
General Information
The Type 549 w ill operate in ambient temperatures up to
122° F (50° C). A minimum of two inches unobstructed clear­
ance around the instrument is recommended for adequate
ventilation. If the internal temperature becomes too high,
a thermal cutout w ill open and disconnect power until the
internal temperature has returned to approximately 115° F.
If this occurs, check to see that air circulation and ventila­
tion are adequate. Constant temperature is important for
accurate operation of the instrument.
The instument requires a minimum 20 minute warm-up
period at ambient room temperature of + 2 5 ° C ± 5 ° C for
rated accuracies.
It is caused by
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