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TRANSDUCERS
The deck assembly contains two
tra~sducers:
speed sensing transducer and
veloc~ty
trans-
ducer.
These transducers provide signals
that are used by the logic chassis and the
controller to generally control the progres-
sion of most machine operations.
Speed Sensing Transducer
The speed sensor (Figure 3-6 and 3-11) gen-
erates a voltage output whenever a ferrous
material (steel pin set in spindle pulley)
enters the magnetic field surrounding the
pole piece at the pickup end of the trans-
ducer.
The logic then shapes this signal
into a 55 microsecond pulse.
As long as the
speed exceeds
3000
rpm, one of these pulses
will be sensed at least once each
20
ms. A
sensing circuit within the logic
m~nitors
the pulse repetition rate and
prov~des
an
enable to Speed relay
K2.
If speed is insufficient,
t~e
pulse r 7 peti-
tion rate is reduced
accord~ngly.
Th~s
has
either of two effects:
1.
2.
If the heads are not loaded,
K2
cannot energize and the logic will
not initiate the load sequence.
If the heads are already loaded,
K2
opens, thereby opening th7 cOil.of.
Retract relay
KS.
The
vo~ce co~l ~s
disconnected from the logic power
amplifier and connected to the -16v
emergency retract capacitor.
The
heads immediately are unloaded to
the retracted stop.
en ' _ _ _
SPINDLE
•
~
PUL~EY
SPEED
~
~SENSOR
55 IJoS PULSES
75148
Figure
3-11.
Speed Detection
83318200
A
Velocity Transducer
The velocity transducer (Figure 3-12) is a
two-piece device consisting of a stationary
tubular coil/housing and a movable magnetic
core.
The magnetic core is connected via the ex-
tension rod to the rear surface of the head/
arm receiver.
All motion of the carriage is
therefore duplicated by the magnetic core.
As the core moves, an emf is induced in the
coil.
The amplitude of this emf is directly
related to the velocity of the core (and
carriage).
The polarity of the emf is an
indication of the direction of movement by
the core (and carriage).
The transducer
output drives an operational amplifier lo-
cated in the logic chassis.
This signal is
used by the servo logic to control acceler-
ation/deceleration of the carriage during
Seek operations.
FIRST SEEK INTERLOCK
~SSEMBLY
The First Seek Interlock assembly provides
a fixed time delay from the completion of
the Start interlocks until heads can be
loaded during the Power On/First Seek se-
quence.
The assembly consists of a motor, reset
switch, cam linkage, and a mounting base.
The base mounts on the deck assembly.
The
motor is energized during the Power On se-
quence and starts a ls-second (approximate)
first seek interlock delay cycle.
The cam
revolves until the reset switch
is~~.
The switch then transfers and removes power
to the motor and signals completion of the
delay cycle to the logic.
If power is lost or dropped during the cycle,
the cam completes the initial cycle upon re-
application of power.
At this time, a new
cycle is initiated if Speed relay
K2
has not
been energized.
Refer to Power On paragraph
for a complete description of conditions
that apply power to the first seek inter-
lock motor.
BLOWER SYSTEM
The blower system (Figure 3-13) provides
positive pressure in the pack area.
The
presence of this elevated pressure results
in an outward dispersion of air preventing
ingestion of contaminated air.
This air
flow greatly reduces possible contamination
and resulting damage to the disk surfaces
and the read/write heads.
Power to the blower drive motor is available
whenever the UNIT POWER circuit breaker is
on.
3-17
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