Du Pont SORVALL RC-5 Service Manual page 104

Son/all®
CentrifugesDrive
System
CircuitThe
main
function of
transfer relay
K407 is to switch the drive motor
from the slow
start+35
V
low voltage circuit
ofQ401 to the main
operating.
230
Vac.
high voltage circuit
ofthe
saturable reactor for acceleration,
then
reverse
the
process
for
deceleration.
Theswitching
of these
two
circuits
Incorporates
varlstors
VR2
and
VR3 that protect
the
cir¬cuit
in
K407
from ac spikes caused
by
the
opening
and closing
of the
relay
contacts.These
two circuits control
the
drive motor operating rate.
During
the
transition,
the
+35V
low voltage circuit and
the
ramp control
circuit
are
both removed from
the drive
motorby
relay
K206.
During
the
SLOW START
operation,
relay
K210 disables the
compressorrelay
circuit, preventing
the
compressor
from operating during
this function, to
protectthe
samples under
test from
vibration.The
main
function of
relay
K206
is to provide a
5-second time delay when
the
drivemotor
accelerates to
900
rpm
or decelerates
to 700
rpm.
This
delay
allows the
drivemotor
brushes to be firmly seated on
the commutator before the transfer relay
switchesthe
drive motor from
a
high
voltage
circuit to a low voltage
circuit
or
reverses the
func¬tion,
as required.
The brushes
are always
in contact
with the drive motor
armaturecommutator.
During
the
circuit transfer, relay
K210
applies
115
Vac to
the
brushspring
motor, causing
it to retract
the
primary
lower brush
spring,
while the
secondaryupper
brush
spring
maintains less tension on
the
brushes
which are always
in
contactwith
the
commutator.
This function occurs
while the drive motor is
using
low
powerand
coasts
to
a slow. gradual
stop.When
the drive motor accelerates above
700
rpm,
if the brake switch is
pressed,
thebrake
circuit
will
be enabled.
Below 700
rpm,
when the brake circuit
is disabled,
thedrive
motor
will
also coast to a gradual
stop.FREQUENCY-TO-VOLTAGECONVERTERFigure
4-9. Automatic Rate
Controller,Simplified
Block
Diagram4-23