Eberline RO-2 - Theory of Operation; General Operation Overview; Functional Theory: Ion Chamber

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A
MODEL RO-2
SECTION HI
THEORY OF
A. GENERAL
Refer
to
Figure
3-1,
a
block
diagram
representing
the
basic
operation
of
the
circuit.
The
ion
chamber
has
bat-
tery
potential
between
the
inside
wall
and
the
center
electrode.
When
the
air
in
the
chamber
ionizes
due
to
radiation,
a
minute
current
flows
through
the
chamber
causing
the
minus
input
lead
of
the
operational
ampli-
fier
to
go
very
slightly
positive.
This
results
in
a
negative
swing
of
the
amplifier
output
which
is
connected
to
the
feedback
elements
through
a
divider
circuit.
The
feed-
back
elements
are
connected
to
the
amplifier
input
and
ion
chamber
and
they
conduct
away
all
of
the
current
generated
in
the
ion
chamber.
The
meter
is
also
tied
to
the
output
of
the
amplifier
and
indicates
in
proportion
to
amplifier
output
voltage.
Range
changing
is
done
by
selecting
different
feedback
elements
and
by
selecting
different.points
on
the
feedback
divider.
B. FUNCTIONAL THEORY
1. Ion Chamber
The
ion
chamber
is
located
inside
the
case
below
the
meter.
It
consists
of
the
lower
two
inches
of
the
three-
inch
diameter
chamber
assembly.
The
remainder
of
the
*VOLTS
ION CHAMBER
FEEDBACK ELEMENTS
| OPERATIONAL
OPERATION
volume
contains
electronic
components,
including
the
amplifier
A1.
The
chamber
wall
is
one-sixteenth
inch
phenolic
and
the
face
is
one
mil
aluminized
Mylar®
,
Another
one
mil
Mylar?
layer
is
glued
to
the
case,
making
total
thickness
of
two
mils.
The
active
volume
of
air
in
the
chamber
is
208
ст.
The inside of the chamber has a conductive coating of
graphite aquadag which is maintained at positive bat-
tery voltage. The inside of the Mylar? face is also at the ``
same voltage. The outside of the chamber is coated with
aquadag and is maintained at ground potential to pro-
vide electrostatic shielding. The center electrode is
coated with conductive aquadag and is supported on the
center conductor of the guarded feedthrough at the top
of the chamber. The guard ring of the guarded feed-
through is positioned on insulators between the center
conductor and the positive outer ring to prevent possible
leakage from the chamber voltage to the center elec-
trode. The guard ring and center electrode are maintain-
ed at the same potential (ground potential) so no
leakage from the guard to the electrode will occur.
The
chamber
is
sealed,
except
for
a
small
hole
iri
the
.
top
wall
which
vents
it
to
the
electronic
section
im-
mediately
behind
the
chamber.
This
section
is
vented
to
the
inside
of
the
main
instrument
case
through
a
plastic
Й
CALIBRATION
AMPLIFIER RESISTORS
FEEDBACK DIVIDER
Figure 3-1. System Block Diagram
CHANGE 2
r