capacitor A1A1C4. As the time constant increases, reset
The differential amplifier is now set to call for an
time increases. This increases stability by slowing the
increase in fuel. Q1A and Q3 are turned on, and Q1B
response time.
and Q2 are at the threshold level. The differential
amplifier remains in this configuration until the speed
A high-frequency feedback circuit consisting of
sensor input nulls out the speed- setting voltage level.
A1A1R16/C8 and A1A1R19/C9 compensates for any
At that time the differential amplifier becomes balanced.
high-frequency interference that might be introduced.
As conduction increases through A1A1Q3, the Q3
Derivative capacitor A1A1C11 provides derivative
collector potential biases output amplifier A1A1Q4 for
control action for the amplifier by effectively acting as
increased conduction. The Q4 emitter potential forward
a short circuit to common for the feedback signal when
biases power amplifier A1Q1, turning A1Q1 on. Power
there is a step change in the output voltage. This allows
amplifier A1Q1 saturates to clamp -9 volt to A1TB1
the amplifier to reach maximum gain momentarily.
terminal 3 and supply the current required by the
Then the effect is dissipated exponentially to zero.
actuator coil.
For single actuator operation, A1TB1 terminal 8 is
System stability is derived by feeding a portion of
connected to dc common terminal 6. For multiple
the output signal back to the amplifier input. GAIN
actuator operation, terminal 8 is connected to the +9-volt
potentiometer A1R1 sets the gain of the amplifier by
power supply at terminal 1.
varying the amount of inverse feedback. As the
amplitude of feedback increases, amplifier gain
Ramp Generator
decreases.
Ramp generator (fig. 9-17) A3 biases the speed
RESET potentiometer A1R2 sets the stability of the
setting input signal to the amplifier module in either of
control loop by changing the reset time constant of the
two modes: a deceleration mode to a low speed or an
feedback signal. The time constant is the product of the
acceleration mode.
value of RESET potentiometer A1R2 and integrating
Figure 9-17.-Ramp generator schematic.
9-25
