Figure 1-47.--Synchronizer, simplified schematic.

When the alternate bridge rectifier conducts, the

the pulse turns it on. By controlling the phase of the gate

voltage across R23 permits C4 (fig. 1-44) to charge,

pulse (with respect to the supply voltage), the firing

introducing the phase delay of the SCR gate pulse.

(delay) angle of the SCR gate may be delayed to any

Firing of SCRs, CR13, and CR14 applies equal potential

point in the cycle up to approximately 180. Through

at both ends of voltage divider R22 and R23. This

control of the firing angle, the average power delivered

removes the voltage drop across R23 and thus allows

to the load can be adjusted.

Q7 to turn off and Q8 to turn on. Thus, the timing

Referring to figure 1-46, you can see that by apply-

capacitor C4 is clamped until the start of the next half

ing a gate pulse at 0 of the phase time axis (view A),

cycle.

output power will be applied during the complete half

cycle. View B shows that power is obtained for a half of

FREQUENCY DISCRIMINATOR

each half cycle by applying a pulse at 90 of the phase

time axis. The other extreme of no output when the

The speed/frequency regulator automatically main-

phase delay is 180 is represented in view C.

tains the motor speed and the generator frequency at a

preset value despite line variations or load changes.

SYNCHRONIZER

Constant output frequency is obtained by auto

The function of the synchronizer is to assure that the

matically adjusting the power to the motor control field

firing angle is always reckoned from the instant the

in response to a frequency discriminator. The frequency

supply voltage crosses the zero axis at each positive half

discriminator converts the generator output frequency

cycle (fig. 1-46, view A). As shown in figure 1-47, when

to a voltage signal that is in direct proportion to the

the SCRs are not conducting, an alternate bridge

speed/frequency of the motor generator.

rectifier circuit is. This alternate bridge consists of diode

CR12, resistor R21, the generator field, resistors R23

The speed/frequency regulator circuit is the same as

and R22, diode CR16, and the secondary of T3. During

the voltage regulator previously discussed. The

the alternate half cycle, the patch (dashed arrows) is the

operational difference is that the voltage regulator

required an increase in generator output voltage to cause

same except diodes CR 11 and CR 17 are used.

Figure 1-47.--Synchronizer, simplified schematic.

1-43