servomotor rotation to correct the off-phase
The pulsating voltage generated at the wiper by
condition. This action occurs provided the phase
the changing grid bias on the tube is the
control potentiometer (fig. 5-23) is set for zero
speed-error voltage. The effect of this voltage is
volts. In this case, the phase difference voltage
discussed later.
actually represents phase error. However, it is
SIGNAL SUMMING. --As you can see by
desirable to have a slave propeller maintain a
specific angle of lead or lag to the master
looking at figures 5-20 and 5-23, the phase-
propeller. The phase control potentiometer then
difference and speed-error voltages couple to the
adjusts to cancel the phase-difference voltage at
signal summing point. Also connected to this
the summing point. For example, to maintain a
point are the limiting circuit, the phase-control
slave lead of 10 degrees from the 180-degree
potentiometer, and magnetic modulator signal
position of the master pulse, the phase control
winding number 2. Any difference in potential
potentiometer adjusts to cancel the phase-
between the signal summing point and the
difference voltage. The phase-difference voltage
feedback potentiometer causes a current in
is generated when the slave propeller leads the
the modulator winding. This results in motor
master propeller by 10 degrees. Thus, when
movement, which, in turn, causes the feedback
the slave propeller leads by 10 degrees, net
potentiometer to null whatever potential is at the
potential at the summing point is zero, and
summing point.
the speed-bias servomotor does not move.
When the slave propeller changes from the
PHASE-ERROR CORRECTION. --When
10-degree lead condition, the phase-difference
the slave propellers aren't on-phase, phase-
voltage changes. The net potential at the summing
difference voltage acts through the averaging
point is the difference between the phase control
circuit to the summing point causing speed-bias
Figure 5-23.-Simplified schematic of signal summing.
5-39
