characteristics found in synchro systems. In general, the load capacity of a synchro system is limited by
the number and types of receiver units loading the transmitter, the loads on these receiver units, and the
Torque is simply a measure of how much load a machine can turn. In torque synchros, only small
loads are turned; therefore, only a small amount of torque is required. The measure of torque is the
product of the applied force and the distance between the point of application and the center of rotation.
For instance, if a 3 ounce weight is suspended from a synchro pulley having a radius of 2 inches, the
torque required to move the weight is 6 ounce-inches. In heavy machinery, torque may be expressed in
pound-feet, but torque synchro measurements are in ounce-inches.
NOTE: The unit of torque is the pound-foot or ounce-inch. Do not confuse this with foot-pounds,
which is the measurement of work. Many times in referring to torque, tools are marked in foot-pounds.
While this use of foot-pounds is technically incorrect, common usage has made it acceptable.
The torque developed in a synchro receiver results from the tendency of two electromagnets to align
themselves. Since the rotor can be turned and the stator usually cannot, the stator must exert a force
(torque) tending to pull the rotor into a position where the primary and secondary magnetic fields are in
line. The strength of the magnetic field produced by the stator determines the torque. The field strength
depends on the current through the stator coils. As the current through the stator is increased, the field
strength increases and more torque is developed.
Q-13. What major factors determine the load capacity of a torque-synchro transmitter?
Q-14. Define the term "torque."
Q-15. What unit of measurement refers to the torque of a synchro transmitter?
OPERATING VOLTAGES AND FREQUENCIES
Military standard and Navy prestandard synchros are designed to operate on either 115 volts or 26
volts. Synchros used in shipboard equipment are designed predominately for 115 volts, while most
aircraft synchros operate on 26 volts.
Synchros are also designed to operate on a 60- or 400-Hz frequency. But like transformers, they are
more efficient at the higher frequency. Operating a synchro at a higher frequency also permits it to be
made physically smaller. This is because the lines of flux produced by the 400-Hz excitation voltage are
much more concentrated than those produced by the 60-Hz excitation voltage. Hence, the core of the 400-
Hz synchro can be made smaller than the core of the 60-Hz synchro. However, some 400-Hz synchro
units are identical in size to their 60-Hz counterparts. This is done so that 60- and 400-Hz units can be
physically interchanged without special mounting provisions. The operating voltage and frequency of
each synchro is marked on its nameplate.
The use of the smaller size synchro permits the construction of smaller and more compact
equipment. The most widely used frequency for airborne equipment is 400 Hz. It is being used
increasingly in shipboard equipment as well. The newer gun and missile fire-control systems use 400-Hz
synchros almost exclusively.
A synchro designed for 60-Hz operation may occasionally be used with a 400-Hz supply. There may
be considerable loss of accuracy, but the synchro will not be damaged. This should be done only in the
case of an emergency when the specified replacement is not available, and system accuracy is not critical.