Sorvall RT/T6000D - Speed Control Knob

System
Descriptions:
Electrical
SORVALL®Centrifuges
6-12.
Speed
Control
Knob
(refer
to
figure
6-10)
The
speed
control knob is
used to
select the
desired run
speed
of
the
rotor.
The
RT/T6000D
and
RT/T6000B
(SNs
9101800
and
above) centrifuges are operated
using a
closed-loop
speed
control
design;
the
desired
run
speed
of the
rotor
is selected
by
turning
the
speed
control knob to
the
corresponding speed
setting on
the
knob.
The
centrifuge constantly
monitors the
actual
speed
of
the
rotor
with
respect
to the
desired
run
speed
and
controls
the motor's
acceleration
and/or deceleration to
obtain the desired
speed.
On earlier
versions
of
the RT/T6000
series
of
centrifuges
(RT/T6000
and RT/T6000B.
SNs
below
9101800),
the desired
speed
is
attained
by
turning
the
speed
control
knob while
watching
the
speed
Indicator, making adjustments accordingly to
obtain the desired
speed;
this
is
an open-loop speed
control
design.
The
speed
control
knob
acts
as
a
voltage
divider between
the
+12
Vdc
and
ground.
Its
wiper
arm
is attached directly to
one Input
of
the
speed
threshold
comparator on
the RT/
T6000B/D
centrifuges
SNs
9101800
and
above.
(On the RT/T6000B,
SNs
below
9101800.
and
RT/T6000
centrifuges
the
wiper
is
open—open-loop
speed
control).
In the
closed-loop
configuration,
this
voltage
on the
wiper
arm represents
the
user's
desired
run
speed.
It
is
compared
to
the
output
from
the
anticipation
circuit that
sums
the actual
RPM
and
the
ACVE
signal.
The
resulting
output
of this
comparison
is
input against
the
triangle
waveform generator
signal to
produce
the
final
Main
PWM
Signal
that
controls
the SCR
firing
angle.
When the
speed
control
knob
is
turned to
a
position
other
than
OFF.
the
speed
control
switch
will
energize
the
speed
control
circuit,
allowing current
to
flow
to
the
motor
(if
the
door
is
closed
and
latched, no errors
exist,
and
the
timer control knob
is
also in
a position
other
than
OFF).
Turning
speed
control
knob
to
OFF
while in
a run
mode
will
terminate
run immediately.
Figure
6-10.
Speed Control
Circuit