revolution. Therefore, consider a 180-degree
that occurs too rapidly for the phase-error circuit
phase difference as an on-phase condition in pulse
to compensate. During an underspeed condition,
the voltage going to the phase difference tube
suddenly changes from positive to negative (fig.
PHASE DIFFERENCE CIRCUITS. --Look
5-22). For an overspeed condition, the voltage
suddenly changes from a negative to a positive.
As you read this paragraph, refer to figure
the voltages the sampling circuits generate at the
grids of the respective tubes. With a 180-degree
5-20. The action of the off-speed circuit is
phase difference signal at the grid of V206A, the
as follows. The underspeed voltage change,
voltage at the wiper of potentiometer RP251
registered in the plate circuit of the phase
adjusts to null or zero volts. This voltage changes
difference tube, couples to the off-speed circuit
through capacitors C253 and C254. The voltage
proportionally with the grid signal from the
change in the plate circuit is positive and the
sampling circuit, and hence represents the phase
reverse bias on diode CR251 is reinforced.
difference between propellers. The following
paragraphs discuss the effect of this voltage on
However, the reverse bias on diode CR252 is
momentarily overcome, allowing capacitor C255
to charge positively. Capacitor C255 discharges
slowly through its parallel resistive network and
OFF-SPEED CIRCUITS. --When the pro-
maintains a grid bias on the off-speed tube V206B.
peller goes off-speed, the sampling circuit senses
(For an overspeed, diode CR251 conducts and
the condition as a sharp voltage change. (When
charges capacitor C255 negatively.) Successive
the slave propeller is on-speed, the slave pulses
occur at the same time interval in each successive
sharp voltage changes add to the charge on
sawtooth cycle.) When an underspeed or over-
capacitor C255 until correction of the off-speed
speed condition develops, the slave pulse occurs
condition occurs. Like the phase difference
at a different position for each sawtooth cycle.
circuit, the off-speed circuit has a zero-volt
At one point, the slave pulse falls up or down the
adjustment potentiometer in the cathode circuit.
Figure 5-22.-Off-speed pulse comparison: (A) slave underspeed; (B) slave overspeed.