Du Pont SORVALL RC-5 Service Manual page 32

Sorvall® Centrifuges
Theory
of
Operation5.
RefrigerationCompressor
operation is similar
to
operation
in
the HOLD
mode.
except
the
tem¬perature
control, programmed by
the blue set pointer, causes ac power
to
Howacross
the
closed contacts
of
relay
K205.The
timing circuit is programmed
for
a
minimum of
40
seconds
OFF
cycle and
anunlimited
time ON
cycle.
This circuit is activated
by
the presence
of
a signal
fromthe
tachometer generator
TG301.6.
Overtemperature
Detection
SystemThe
overtemperature detector consists
of
a
signal
comparator,
control amplifier
andrelay
K4.
If the
temperature
rises above the red set
pointer,
a temperature
signal
isgenerated
by
the
comparator
to
open
the overtemperature switch triac
CR20
anddeenergize
run-hold relay K205. placing
the centrifuge in the
HOLD
mode.7.
Brush
Warning
SystemThe
brush
warning system consists
of
circuit breakers
CB 1 and CB2 and
two
nor¬mally
open
brush switches in the drive
motor.
As the brush
wears,
the
switchslowly
closes,
until
contact
is
made, connecting ac
motor
voltage
to its
correspond¬ing
circuit
breaker through a
250-ohm
resistor. Voltage above
12
to
20
volts
tripsthe
breaker.
The
tripped circuit
breaker
opens
the 115 Vac
connection between
run-hold
relay
K205
and
ON
switch
Sill
which energizes thermal relay K207.
Thermalrelay
K207
switches
ON
and
OFF
providing an intermittent voltage to
BRUSHESindicator
lamp
DS103. When circuit breakers
trip, remaining
brush life is
approxi¬mately
10
hours. Once
the
run
is
completed,
the centrifuge will
not restart until
thecircuit
breakers
are
reset.8.
Motor
BrakingThe
motor
brakes
only
as the centrifuge enters or is in the
HOLD
mode.
However,the
braking function
can be set at
any
time. Pressing
BRAKE
switch
S109A
ener¬gizes
brake
relay
K208
to
apply
+5 Vdc
to contact
9 of
motor relay K202.
PressingOFF
switch
Sl 10
deenergizes
motor
relay
K202
to
apply
the +5 Vdc
to
the
Junctionof
resistors R201 and R202
to
brake the
motor.
BRAKE
lamp
DS109
is energized
by30
Vac through S
109B.3-3.
RC-5B
Theory
of Operation (figures
3-11
through3-24)The
theory
of
operation for the
RC-5B
centrifuge Is similar to
that
of the RC-5, with
thefollowing
exceptions:a.
Operational
ModesThe
RC-5B
is capable of
operating
in the
HOLD
or
TIMED
modes.
Under normal
condi¬tions,
the
compressor
will
continue
to
operate
in the
STOP
mode.
The
RC-5B
will
alsooperate
In the SLOW
mode when equipped
with the optional automatic
rate
controller.3-5