Federal Signal Corporation PA300 Series 690009, Инструкции по установке, обслуживанию и эксплуатации

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SECTION V SECTION V
CIRCUIT DESCRIPTION CIRCUIT DESCRIPTION
5 5--1 1.. G GE EN NE ER RA AL L..
The Model PA300 circuitry can be divided into The Model PA300 circuitry can be divided into
seven functional blocks. Refer to figure 5-1 and 6-4 seven functional blocks. Refer to figure 5-1 and 6-4
while reading the following paragraphs.
while reading the following paragraphs.
5-2 5-2.. RA RATE O TE OSCI SCILL LLATO ATORS A RS AND V ND VOL OLTAG TAGE E
CONTROLLED OSCILLATOR. CONTROLLED OSCILLATOR.
The heart of the Model PA300 circuitry is the The heart of the Model PA300 circuitry is the
rate oscillator and VCO sections. The rate oscillator rate oscillator and VCO sections. The rate oscillator
not only determines the cycling rate of each
not only determines the cycling rate of each siren siren
tone, but also generates the control voltage that tone, but also generates the control voltage that
operates the voltage controlled oscillator
operates the voltage controlled oscillator (VCO). The (VCO). The
VCO generates a squar VCO generates a square-wave output whose f e-wave output whose fre- re-
quency is directly proportional to the control voltage. quency is directly proportional to the control voltage.
The output of the VCO is coupled to the siren’s
The output of the VCO is coupled to the siren’s power power
output amplifier. output amplifier.
The siren rate oscillator consists of The siren rate oscillator consists of an LM556 an LM556
dual timer configured as two astable oscillators. The dual timer configured as two astable oscillators. The
first astable oscillator (IC12A) employs analog
first astable oscillator (IC12A) employs analog
switches (IC10A , IC10B) to select the resistance for
switches (IC10A , IC10B) to select the resistance for
the RC timing network which determines the astable
the RC timing network which determines the astable
oscillator’s cycling rate. IC10C , another analog
oscillator’s cycling rate. IC10C , another analog
switch, connects the discharge pin of IC12A to the RC
switch, connects the discharge pin of IC12A to the RC
timing network. When the peak function is called for,
timing network. When the peak function is called for,
Figure 5-1. Functional Block Diagram. Figure 5-1. Functional Block Diagram.
-10- -10-
the control pin (IC10-6) goes low putting the switch the control pin (IC10-6) goes low putting the switch
in a high impedance state (OFF), and allows the RC
in a high impedance state (OFF), and allows the RC
rate capacitor (C11) to charge as the siren tone
rate capacitor (C11) to charge as the siren tone
peaks.
peaks.
IC12B, another astable oscillator, generates the IC12B, another astable oscillator, generates the
control voltage required to generate the air-horn control voltage required to generate the air-horn
sound. Normally, IC12B is held in the reset state
sound. Normally, IC12B is held in the reset state
(IC12-10 low) until the air horn control line is pulled
(IC12-10 low) until the air horn control line is pulled
high.
high.
IC8C, a one-of-two analog switch, selects the IC8C, a one-of-two analog switch, selects the
siren or air horn control voltage from IC12A or siren or air horn control voltage from IC12A or
IC12B. IC8B selects either the RC control voltage
IC12B. IC8B selects either the RC control voltage
(manual, wail and yelp modes) or the square wave
(manual, wail and yelp modes) or the square wave
control voltage (hi-lo) derived from the output of
control voltage (hi-lo) derived from the output of
IC12A. The voltage divider network of
IC12A. The voltage divider network of R27, R28, R29 R27, R28, R29
and CR8 provides the DC level shifting of the IC12A and CR8 provides the DC level shifting of the IC12A
output necessary to obtain the desired hi-lo tone
output necessary to obtain the desired hi-lo tone
frequencies.
frequencies.
IC13, a phase-locked loop, contains the voltage IC13, a phase-locked loop, contains the voltage
controlled oscillator. C21, R46, R47, R57, and the controlled oscillator. C21, R46, R47, R57, and the
control voltage on pin 9 determine the output fre-
control voltage on pin 9 determine the output fre-
quency.
quency.