The receiver, or synchro motor, is
electrically similar to the synchro generator. The synchro
receiver uses the voltage
generated by each of the synchro generator windings to
position the receiver
rotor. Since the transmitter and receiver are electrically
similar, the angular position of the
receiver rotor corresponds to that of the synchro transmitter
rotor. The receiver differs mechanically
from the transmitter in that it incorporates a damping device
to prevent hunting. Hunting
refers to the overshoot and undershoot that occur as the
receiving device tries to match the
sending device. Without the damping device, the receiver
would go past the desired point slightly,
then return past the desired point slightly in the other
direction. This would continue, by
smaller amounts each time, until the receiver came to rest at
the desired position. The damper prevents
hunting by feeding some of the signal back, thus slowing down
the approach to the desired
point.
Differential synchros are used with
transmitter and receiver synchros to insert a second signal.
The angular positions of the
transmitter and the differential synchros are compared, and
the difference or sum is
transmitted to the receiver. This setup can be used to
provide a feedback signal
to slow the response time of the receiver, thus providing a
smooth receiver motion.
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 T2.
Figure T2
When the transmitter’s shaft is turned, the
synchro receiver’s shaft turns such that its
"electrical position"
is the same as the transmitter’s. 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 transmitter
shaft.
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