Q-62. When is a synchro receiver (TR) properly zeroed?
Q-63. What should a voltmeter read when a TX is set on coarse zero?
Q-64. What precaution should you take when you use 115 volts to zero a differential?
Q-65. Why should a synchro be rechecked for zero after it is clamped down?
Q-66. What is the output voltage of a CT when it is set on electrical zero?
Q-67. When you zero a multispeed synchro system which synchro should you zero first?
ELECTRICAL LOCK METHOD
The electrical lock method, although not as accurate as the voltmeter method, is perhaps tile fastest
method of zeroing synchros. However, this method can be used only if the rotors of the units to be zeroed
are free to turn and the lead connections are accessible. For this reason, this method is usually used on the
TR because, unlike transmitters, the TR shaft is free to turn.
To zero a synchro by the electrical lock method, deenergize the unit, connect the leads as shown in
figure 1-41, and apply power. The synchro rotor will then quickly snap to the electrical zero position and
lock. If the indicating device connected to the synchro shaft does not point to zero, loosen the synchro in
its mounting and rotate it until the zero position of the indicator corresponds with the electrical zero of the
synchro. As we stated previously, you may use 115 volts as the power source instead of 78 volts,
provided you do not leave the unit connected for more than 2 minutes.
Figure 1-41.Zeroing a synchro by the electrical lock method.
Two types of synchro testers are shown in figure 1-42, view (A) and view (B). Each is nothing more
than a synchro receiver on which a calibrated dial is mounted.