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a FG AMP
In order to square the waveform
of the signal
obtained
from
the speed sensor section (output:
0.5 — 2.0 mV rms) prior to inputting it into the
F/V converter, it is amplified 69dB across a band
width of 20 to 160Hz.
= F/V Converter
1.
Since the rotational speed is detected at a fixed
frequency,
the frequency
must
be converted
to a voltage (DC).
This function is performed
by the F/V converter.
2.
Previously
(in PA2004)
this was
done
by a
2-frequency F/V converter, however, increasing
control gain of PA2007 allows a signal-frequen-
cy F/V to be used.
3.
F/V converter gain does not change even with
rpm changes.
4.
Switching reference frequency is shown in Fig.
4-5,
When the switch is OFF, speed is set to 33 1/8
rpm, and when
the switch is ON, the variable
resistor
used
by
33
1/3
rpm
is connected
parallel to the 45 rpm variable resistor.
The
resulting
total
impedance
establishes
rotat-
ional speed.
Thus, each time 33 1/3 rpm is
adjusted, 45 rpm must also be adjusted.
This
arrangement
prevents
any
rotational
instabi-
lity that might result from both switches being
temporarily OF F when speed changes are made
by switching from 33 1/3 —45 rpm.
5.
Co, Ct, Rt, and Rfv are each connected
to
ground, but the grounding point is very close
to that of PA2007.
Also,
Rt is a 0.01
uF
ceramic
capacitor
for
noise
and
oscillation
removal,
and
it is grounded
in close
prox-
imity to PA2007 too.
Rt
z 33 1/3 r.p.m
.
7
Fig. 4-5 Switching reference frequency
45 r.p.m
=
Reference Phase Generator IC PD1003
When
power is turned ON, the X'tal oscillator
block
generates
a 6.144 MHz
signal by using
the externally connected crystal oscillator.
2.
This is reduced to 1.5kHz by divider circuit 1
(1/4096), then this divided signal is input to
divider circuit 2.
| a
iele
3.
The
6kHz
signal input to divider circuit 2 is
further divided 1/27 for 33 1/3 rpm operation,
and
1/20 for 45 rpm, then transmitted from
pin 15 to PA2007 pin 7.
33 1/3 rpm: 55.5Hz
45 rpm: 75Hz
= P/V Converter
The signal received at the 7 pin (item above) is
input
to the
P/V converter.
The P/V converter
serves to convert the reference phase to DC volt-
age.
The reference phase converted into DC voltage
is combined
(by
the buffer
amp
and
resistor)
with the DC voltage from the F/V converter (and
used for rotation speed) and transmitted from pin
11 as a motor
rotation speed control, signal to IC
PA2008
pin 6, then finally to the absolute value
amp (Fig. 4-6).
Fig. 4-6 (F—V) + (P—V) circuit
= Phase-lock Discriminator Circuit
When
phase
control
is in effect,
the
output
characteristics
of the F/V converter appear as in
Fig. 4-7.
The
portion that shows no change in
speed when load torque is varied up and down can
be considered
as the
phase-locked area, and the
portion where large rotational speed changes occur
(as in Fig. 4-8)
is outside the phase-locked area.
Thus,
F/V
converter
output
can
be
input into
an absolute value comparator having an upper and
lower
threshold.
A theoretical diagram of such
a circuit is shown in Fig, 4-9.
Noise
(Vout)
/
8.0
3.5
fo
(Hz)
Noise
Fig. 4-7 input/output characteristics
15
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