Figure 2-6.--Coarse eletrical zero markings.

Figure 2-5.--Transmission system diagram; standard connections of a simple synchro.

Regardless of the synchro to be zeroed, there are

synchro units is electrical zero. The mechanical

reference point for the units connected to the synchros

two major steps in each procedure. The first step is the

depends upon the particular application of the synchro

coarse or approximate setting. The second step is the

system. Whatever the application, the electrical and

fine setting. The coarse setting ensures the device is

mechanical reference points must be aligned with each

zeroed on the 0 position rather than the 180 position.

other. The mechanical position is usually set first, and

Many synchro units are marked in such a manner that

then the synchro device is aligned to electrical zero.

the coarse setting may be approximated physically by

Each type of synchro has a combination of rotor position

aligning two marks on the synchro. On standard

and stator voltages that is its electrical zero.

synchros, this setting is indicated by an arrow stamped

There are various methods for zeroing synchros.

on the frame and a line marked on the shaft, as shown

Some of the more common zeroing methods are the

in figure 2-6. The fine setting is where the synchro is

voltmeter and the electrical lock methods. The method

precisely set on 0O.

used depends upon the facilities and tools available and

how the synchros are connected in the system. Also, the

method for zeroing a unit whose rotor stator is not free

to turn may differ from the procedure for zeroing a

similar unit whose rotor or stator is free to turn.

Voltmeter Method

The most accurate method of zeroing a synchro is

the ac voltmeter method. The procedure and the test-

circuit configuration for this method vary somewhat,

depending upon which type of synchro is being zeroed.

Transmitters and receivers, differentials, and control

transformers each require different test-circuit con-

figurations.

For the ac voltmeter method to be as accurate as

possible, an electronic or precision voltmeter having a

0- to 250-volt and a 0- to 5-volt range should be used.

On the low scale, this meter can also measure voltages

Figure 2-6.--Coarse eletrical zero markings.

as low as 0.1 volt.

2-5