Broadband Amplifiers

as compared to the input impedance of broadband amplifier Q1 (processor). With multiple preamplifiers connected in

parallel, the combined impedance of the worst condition (twenty) would not swamp the input to the broadband amplifier

Q1.

b. Broadband Amplifiers. The input to the processor from the preamplifier in the detector, is coupled into

broadband amplifier Q1 which has a parallel fixed tuned L-C circuit that is resonant at approximately 15 kHz which is the

high end of the equipment band pass range. The output of Q1 is coupled into the second broadband amplifier Q2 which

has a parallel fixed tuned L-C circuit that is resonant at approximately 10 kHz which is the low end of the equipment band

pass range. Output from Q2 is coupled into the third broadband amplifier Q3 which has a parallel fixed tuned L-C circuit

that is resonant at approximately 12.5 kHz which falls in the center of the equipment band pass range. The combined

resonant circuits of the three broad-band amplifiers results in a relatively flat frequency response between 10 kHz and 15

kHz and rejects frequencies outside of the band that are associated with naturally occurring phenomena.

c. Detection Circuits. The output from broadband amplifier Q3 is coupled directly to the amplifier (Q4 and Q5).

Transistors Q4 and Q5 are direct coupled and provide additional gain for driving envelope detector CRT. Output from

the envelope detector CR1 is impressed on the base of the threshold detector Q6 which operates at approximately plus

0.6 volts and fires the one shot multivibrator (MV) Q7 and Q8. The output pulse from the one shot multivibrator (test

point MV) will persist for approximately 1.5 seconds (momentary threshold exceeded) or from a threshold exceeded

period plus 1.5 seconds (fig. 6-2). During no detected vibration, the voltage level at test point MV is approximately zero

and during detected vibrations, the voltage level at test point MV rises to approximately 11 volts (length of time voltage

present is determined by the one shot multivibrator). Integrator gate Q9 is normally conducting when the one shot

multivibrator is inactive and when in this state it discharges R-C integrator R34 and C18.

When one shot multivibrator is activated, integrator gate Q9 is cut off and the R-C integrator starts charging (fig.

6-2). Following the prescribed detected duration period of vibration, the R-C integrator reaches a threshold level of

approximately 3 volts. Threshold detector Q10 will conduct and operate the one shot multivibrator Q11 and Q12 which

turns off alarm relay driver Q12. Relay K1 becomes deenergized and its respective contacts open to signal a detected

vibration motion.

During a state of no alarm, Q12 is conducting to hold relay K1 in the energized position. When the alarm is

activated, Q12 goes into a nonconducting state for a period of approximately 0.7 seconds. If the detected vibration is

maintained for a long period, the 0.7-second alarm signal will repeat every 4.5 seconds. If a loss of power is

encountered, relay K1 would also deenergize and signal an alarm. When Q12 returns to a conducting state (no detected

vibration) relay K1 is again energized, and integrator discharge Q13 is driven into conduction which discharges integrator

capacitor C18.

6-4. DC Voltage Regulation

Power for operating the processor and the detector is provided by J-SIIDS control unit in the form of +20 + 2 Vdc. A

block diagram of the power regulator is shown in figure FO-2 (located in rear of manual). Diode CR5 in the positive line

of the input +20 Vdc offers circuit protection against accidentally reversing the input power polarity connection to the

processor. Voltage regulator Z1 regulates the input dc power at an output of + 12 Vdc which is used throughout the

processor/detector vibration signal.

6-2