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.

SYNCHRO TESTERS

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.

Figure 1-42A. - Synchro Testers:

Figure 1-42B. - Synchro Testers:

These testers are used primarily for locating defective synchros. Although they do provide a method for zeroing synchros, they should not be relied on without question. It is possible for the calibrated dial to slip from its proper position, and since the dial is graduated only every 10, it is difficult to read small angles with accuracy. Therefore, the synchro tester method of zeroing synchros is potentially less accurate than those previously described. To zero a TX, CX or TR using a synchro tester, use the following procedure:

Connect the synchro tester as shown in figure 1-43.

Figure 1-43. - Zeroing a synchro using a synchro tester.

Set the unit whose position the TX or CX transmits accurately on zero or on its reference position. In the case of the TR, set its rotor to zero or to its reference position. Turn the stator of the synchro being zeroed until the synchro tester dial reads 0. The synchro is now approximately on electrically zero. Momentarily short S1 to S3 as shown. If the synchro tester dial moves when S1 is shorted to S3, the synchro is not zeroed. Check the tester dial to ensure it has not slipped. If the tester dial has not slipped, move the synchro stator until there is no movement when S1 and S3 are shorted. This is the electrical zero position of the synchro being aligned.

Q.68 What method of zeroing a synchro is perhaps the fastest but NOT necessarily the most accurate?
Q.69 What restrictions are placed on the use of the electrical lock method?
Q.70 When you zero a synchro with a synchro tester, what is indicated by a jump in the synchro tester's dial when the S1 and S3 leads are momentarily shorted?