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Theory
of
Operation
Sorvall®
Centrifuges2.
Door
InterlockInterlock
door
latch
switch
S301
prevents
the
centrifuge
from
operating
when
thedoor
Is
open
and
the
controls
are
set
In
the
RUN
mode.
The
centrifuge
can
enter
theRUN
mode
with
the
door
open
by
depressing
both
the
DOOR
switch
S301
and
theON
switch
Sl
11
at
the
same
time.The
centrifuge
door
can
be
opened
during
a
RUN
cycle,
without
stopping
the
rotordrive
motor.
This
is
done
by
pressing
the
DOOR
switch
and
opening
the
door
latchat
the
same
time.3.
Speed
ControlThe
centrifuge
drive
motor
speed
is
controlled
by
a
dc
signal
generated
in
the
speedcontrol
circuit.
This
signal
is
applied
to
the
control
winding
of
the
saturable
reactorthrough
contacts
4-7
and
6-9
of
the
speed
control
relay
K206.
Its
limits
are
con¬trolled
by
torque
trimmer
potentiometer
R204.The
speed
control
circuit
consists
of
a
rpm
indicator
Ml
01.
a
tachometer
generatorTG301,
a
speed
set
comparator,
a
high
gain
amplifier,
and
a
power
amplifier.Speed
is
controlled
by
the
resistance
in
speed
control
potentiometer
R
106
againstan
ac
signal
generated
at
the
tachometer
generator
TG301.
This
signal
is
propor¬tional
to
the
rpm
of
the
centrifuge
drive
motor.Until
the
comparator
makes
a
comparison,
the
high
gain
and
power
amplifiers
areoperating
at
full
output
power,
thereby
saturating
the
control
winding
of
the
satu¬rable
reactor.
This
function
causes
the
centrifuge
drive
motor
to
operate
at
maxi¬mum
motor
acceleration.
When
the
signal
from
the
tachometer
generator
reaches
apreset
level,
it
is
compared
against
a
comparator
generated
signal.
The
comparatorthen
causes
the
power
amplifier
to
be
driven
into
the
cutoff
region.
This
causes
thepower
amplifier
to
cut
off,
reflecting
a
line
voltage
drop
across
the
reactor
instead
ofthe
drive
motor.
As
the
motor
speed
varies,
above
or
below
the
preset
level,
thepower
amplifier
modulates
the
reactor
accordingly.
The
reactor
cycles
the
drivemotor
ON
and
OFF
as
necessary
to
maintain
a
preset
rpm
controlled
by
the
resis¬tance
of
control
potentiometer
R106.The
tachometer
output
is
read
directly
at
the
speed
indicator
as
actual
rpm.4.
Overspeed
Detection
SystemThe
overspeed
detector
consists
of
a
tachometer
signal
detector,
a
signal
compara¬tor
and
control
relay
K205.
A
reference
level
corresponding
to
22
000
rpm
is
pro¬grammed
into
the
comparator.
The
output
of
the
tachometer
generator
TG301
is
anac
voltage
which
goes
to
the
comparator
where
it
is
converted
to
a
compatible
signalthat
is
compared
against
a
signal
generated
in
the
comparator.
If
the
tachometergenerator
signal
exceeds
the
preset
voltage
level,
a
signal
is
generated
which
opensthe
overspeed
switch
and
deenergizes
the
RUN/
HOLD
relay
K205,
removing
powerfrom
the
centrifuge
drive
motor
and
placing
the
centrifuge
in
the
HOLD
mode.3-4
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