Sorvall RT/T6000D - Page 125

System
Descriptions:
Electrical
SORVALL®
Centrifuges
Reference Voltage
(Desired
Set
Speed)
Maximum
Speed Adiust
L
set Run SPeed
l5
PotentioiTieter
—>
(Front Panel)
Figure
6-20.
Open-Loop Speed
Control Circuit
6-23.
Brake Circuit
(continued)
as
the
armature
spins
through
the
excited
field. A 5
ohm,
50
watt
brake resistor is
used
to
limit
the
current through
the
RUN/BRAKE
relay
K
1
during braking;
the
motor
becomes
a
generator
during
this
period.
The
brake
transformer
that
supplies
the
rectified
voltage
into
the
field
windings
for
excitation is
controlled
by
the
front
panel
BRAKE
control switch
SW3
through
additional
circuitry.
The
brake circuit is
turned
off
automatically
by
hardware when
the
speed
is below
200
rpm,
regardless
of the BRAKE switch
position,
to
allow
the
rotor
to coast smoothly
to
a
full
stop
(refer to
paragraph
6-24.
200
RPM
Switch).
Figure
6-21. Brake
Circuit
6-26