101
3. 1.5. 4.
FAST
MODE
Before
writing
in
this
mode,
the fast
and
front
meshes
should
first
be
erased
and
prepared.
The
writing
beam
can
then
write
into
the
fast
mesh
and
the
recorded
waveform
is
transferred
as soon
as possible
after
that
to the
front
mesh.
The
storage
layer
of
the
fast
mesh
has
a low
capacitance,
which
gives
a high
writing
speed
but a
low
storage
time.
The
front
mesh
is the
type used
in
conventional
storage
calhode-ray
tubes
and
has
the
facility
of
variable
persistence
operation.
A
complete
erase/prepare
-
write
-
transfer
cycle is now
described. The
voltage
waveforms
that are
applied
to
the
storage
electrodes
are
shown
in Fig.
3.3.
In
order
to
erase/prepare,
the
front
mesh is
connected
to a +500
V, 100
ms
pulse
(the
first erase
pulse)
and
then
returned
for 500
ms
to its original
potential of
approximately
0 V.
This
first erase
pulse
starts
immediately
after
the ERASE
pushbutton
is
released.
After
the 500 ms zero
potential
period there
is
a second
erase
pulse of
about 10 V
applied to the front
mesh for 900
ms. At the
end of this
pulse
the mesh is
applied
to a potential
that
is somewhat
lower
than the zero
potential.
This level is
adjustable
and controls
the sensitivity
of the
fast
mesh after its
preparation.
During
the
preparation
period of
the front
mesh, at 300 ms after
the start
of the second
erase pulse,
the fast
mesh
is lowered from 140
V to
about
+5
V in order to prepare it.
At the
end of the
second erase
pulse of the front mesh
the storage section
is
ready
to be written
in. The
erase/prepare
-
write
-
transfer
cycle is interrupted
here and the storage
system waits
for the
time-base sweep
that writes
the fast
mesh. During
the waiting period the charge
condition of the
fast mesh is stabilised
by pulses
with an upper
level of
+140
V.
These stabilising
pulses
have
a 150 Hz
frequency and
a duty cycle of 0.07 %.
Immediately
after
the time-base sweep
has ended
and the fast
mesh has
been written
into,
a transfer
pulse of +500V,
100 ms
duration,
is applied to the front
mesh.
During
this transfer
pulse,
the
fast mesh potential is slightly
lowered.
The charge pattern
on the fast mesh has now
been
transferred
to the front mesh.
During
the whole erase/prepare
-
write
-
transfer cycle
of the
storage
meshes the
collimator electrodes
3,
2 and
1,
and
the
flood
gun accelerator are
pulsed in the
positive
direction.
Figure
3.3. also shows
a time-base blocking
signal and the time-base sweep. The time-base
is
unblocked from
100
ms after
the
end
of the second erase pulse until the start of
the time-base sweep; only
during
this
period
can it respond to a trigger signal.
3.
1.5. 5. STORE MODE
In this mode,
the storage electrodes
of
the
c.r.t. are
applied
to constant d.c. voltages. Only the flood gun
accelerator is
pulsed,
using
a 100 Hz square
wave
with
an
upper
level of
+20
V and a lower level of 0 V. The
duty
cycle is adjustable
between 0 and 80 % by means of the INTENS control (R14). A duty cycle of 80 %
gives a maximum brightness
of the recorded waveform and
0
%
gives
a
blanked
display.
The remaining storage electrodes are
applied
to
constant d.c. voltages, typically
as follows:
—
front mesh voltage between
—5
V
and +15
V,
—
fast mesh
voltage of
+140
V,
—
collector
mesh voltage of
+1
50 V,
—
3rd collimator
voltage
of +75
V,
—
2nd
collimator voltage of between
+30
V
and
+90
V,
—
1st collimator
voltage
of
30 V,
—
the time-base
is
continuously
blocked.
3.
1.
5. 6.
NON
STORE MODE/MEMOR Y
OFF
In
this mode
the
storage
system of the
c.r.t.
is
switched off and the storage electrodes are applied
to constant
d.c. voltages,
typical values
being
as
follows:
—
front mesh
at
—35
V,
—
fast mesh at
+140
V,
—
collector mesh at
+1
50 V,
—
3rd collimator at +75 V,
—
2nd collimator
at
+30 V
to
+90
V,
—
1st
collimator
at +30 V,
—
flood gun accelerator at
+20
V.
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