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Sorvall®
CentrifugesRefrigeration
System230
Vac
^-115
VacT201ftCR23\r230
VacRET7/79RCS/43Figure
5-3.
Refrigeration
Electrical
Circuit,Simplified
Schematic
Diagram
(RC-5B)5-5.
Temperature
Control
CircuitThe
temperature
control
circuit
consists
of
a
resistance
temperature
detector
(RTD),
atemperature
meter
assembly
M102.
and
associated
circuitry.
The
RTD,
which
is
a
tem¬perature
sensitive
resistor,
is
located
in
the
rotor
chamber
and
is
connected
to
one
leg
ofa
resistance
bridge
circuit.
The
bridge
is
balanced
at
a
minimum
temperature
so
thatzero
current
flows
through
the
meter.
As
chamber
temperature
rises,
the
RTD
resis¬tance
increases
and
unbalances
the
bridge,
forcing
current
through
the
meter
coll.
Theblack
meter
pointer
moves
upscale,
indicating
increasing
temperature.Two
front
panel
knobs
adjust
the
position
of
two
additional
pointers
—
the
blue
pointerfor
setting
the
RUN
mode
temperature
and
the
red
pointer
for
setting
the
HOLD
modetemperature.
Attached
to
the
lower
end
of
each
of
these
pointers
are
a
pair
of
miniaturephotocells.
Attached
to
the
lower
end
of
the
black
pointer
is
an
arc
shaped
attachmentdesigned
to
block
the
photocell
when
the
black
pointer
approaches
either
the
blue
or
redpointer,
and
provide
a
signal
to
the
temperature
control
circuit.Supply
voltage
for
the
red
pointer
photocell
is
provided
by
the
+5
Vdc
temperature
con¬trol
power
supply
through
variable
resistor
R42.
As
the
centrifuge
warms
up,
the
blackpointer
will
block
the
corresponding
photocell,
increasing
its
resistance
in
the
circuit,and
provide
a
signal
to
activate
the
refrigeration
circuit.Supply
voltage
for
the
blue
set
pointer
photocell
is
also
provided
by
the
temperaturecontrol
power
supply,
applied
through
variable
resistor
R43.
As
the
centrifuge
warmsup,
the
black
pointer
will
unblock
the
corresponding
photocell,
reducing
its
resistancein
the
circuit,
and
provide
a
signal
to
activate
the
refrigeration
system.5-5
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