5.3.2.4 Tachometer Amplifier
The
Tachometer Amplifier shown on Schematic No. 102810, sheet 1, amplifies and inverts
the velocity feedback signal from velocity transducer. This feedback signal
is
routed from
pin 9
of
J203
(zone A15) to the input
of
U14
(zone G14).
U14
is
a Type
741
operational
amplifier which is used as a summing amplifier. Potentiometer
R204
provides offset
balance adjustments
for
U14.
When Reverse Slow Mode (NLRSM1) at pin
23
of
J201
is
low
and Heads Retracted
(SHRXG) at pin
28
of
J202 is high (Le., when the positioner servo is in the Reverse Slow
Mode
and
the heads are retracted)
all
(zone
G14)
turns on and the output of velocity
transducer is grounded. This action removes the velocity feedback signal from the input
of
U14
and causes the output
of
U14
at
TP16
to
go
to
Ov.
5.3.2.5 Summing Amplifier
The
Summing Amplifier
U16
(zone
G13)
is shown on Schematic No. 102810, sheet 1. This
amplifier sums the following reference, feedback
or
control signals
of
the positioner servo
system.
(1)
Velocity reference signal.
(2)
Velocity feedback signal.
(3)
(X
+
0)
position feedback signal.
(4)
Offset signal.
(5)
Track offset-plus and track offset-minus signal.
(6)
Reverse slow velocity mode, forward slow velocity mode, and reverse slow
and
heads up velocity mode signal.
(7)
External perturbation input signal.
(8)
Temperature compensation and head alignment
(200
tpi).
The positioner servo system normally operates in the Velocity Mode. Velocity feedback is
provided continuously except when Reverse
Slow Mode (NLRSM1) is low and Heads
Retracted
(SHRXG) is high, i.e., the servo is in the Reverse Slow Mode and the heads are
retracted. At this point velocity feedback is cut off.
The Velocity Reference Enable signal (NLVREG) (pin
20
of
J201) going low turns
on
03
(zone
F15)
and enables the velocity reference signal from
TP9
into the summing junction
of
U16
(zone G13). The Position Mode signal (LPMXG) (pin
22
of
J201) going high turns
on
013 (zone
G13)
enabling the X + 0 signal from
U7
(zone
F14)
into the summing junction
of
U16.
Thus, the servo is placed in the Position Mode.
The
Forward Slow Mode signal (NLFSM1) low, and the Reverse Slow Mode signal
(NLRSM1) high at pins
24
and
23
of
J201, respectively, introduces a Forward Slow Mode
signal (at
TP10)
into the summing junction
of
U16.
This
can
be monitored at
TP10
(zone
D16).
Conversely, NLFSMl high and NLRSMl low introduces a Reverse Slow Mode signal
(monitored at
TP10)
into the summing amplifier.
Track Offset
Plus (NLTOPG) and Track Offset Minus (NLTOMG) signals are introduced at
the summing junction
of
U16
only when the servo is in the Position mode of operation.
NL
TOPG
(pin
26
of
J201) low and NLTOMG (pin
25
of
J201) high introduces the Track
Offset
Plus signal; NLTOPG high and NLTOMG low introduces the Track Offset Minus
signal into the summing junction
of
U16.
These signals
can
be monitored at
TP11
(zone
E16.)
TP19
is provided to introduce
an
external perturbation Signal into the summing
junction.
Potentiometer
R22
(zone
F16)
is provided
for
nulling the X + 0 signal
in
reference to servo ground.
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