Control transformer synchros are used when only a voltage indication of angular position is
desired. It is similar in construction to an ordinary synchro except that the rotor windings are
used only to generate a voltage which is known as an error voltage. The rotor windings of a
control transformer synchro are wound with many turns of fine wire to produce a high
impedance. Since the rotor is not fed excitation voltage, the current drawn by the stator windings
would be high if they were the same as an ordinary synchro; therefore, they are also wound with
many turns of fine wire to prevent excessive current.
During normal operation, the output of a control transformer synchro is nearly zero (nulled) when
its angular position is the same as that of the transmitter.
A simple synchro system, consisting of one synchro transmitter (or generator) connected to one
synchro receiver (or motor), is shown in Figure 2.
Figure 2 Simple Synchro System
When the transmitters shaft is turned, the synchro receivers shaft turns such that its "electrical
position" is the same as the transmitters. What this means is that when the transmitter is turned
to electrical zero, the synchro receiver also turns to zero. If the transmitter is disconnected from
the synchro receiver and then reconnected, its shaft will turn to correspond to the position of the