Sec. 1-2] 



MECHANICAL INPUT TRANSDUCERS 



61 



induces voltages in the stator windings ; the magnitude of the voltages 

 induced in each stator winding depends upon the angular position of 

 the rotor. The voltages across each of the three stator windings are 

 all in phase, but their amplitudes vary with the sine of the angle 

 between the coil axes! 



If the stator windings are arranged at 120°, the voltages are 



E 



sin 'lirft sin 

 -- ^x sin 2irft sin {0 + 120°) 

 E max sin 27rft sin {0 + 240°) 



max 



^2 • - ^max 



j&max is the peak voltage induced in each stator coil and/ the frequency 

 of the alternating voltage applied to the rotor. For a given set of 

 stator voltages, there is only one corresponding rotor position. 



Synchros can be used for the transmission of angular position infor- 

 mation to a remote location. In a simple arrangement, the stator 

 windings of a synchro "generator" 

 are connected to the correspond- 

 ing stator windings of a synchro 

 "motor," as shown in Fig. (1-2)43. 

 The generator and motor are elec- 

 trically identical, but the motor is 

 equipped with some mechanical 

 damping. The rotors of both units 

 are connected to the same power 

 source; the angular displacement 

 of the motor follows that of the 

 generator. 



Synchros can be used for a range of rotation of 360°. The torque 

 required to drive the rotor of a synchro depends upon the stator 

 current, which varies with the external load. For a high impedance 

 load ( > 1,000 ohms) , the driving torque required is only that necessary 

 to overcome bearing friction (order of 3 x 10 3 dyne-cm and higher, 

 increasing at lower temperature) and inertial force. However, if the 

 currents in the stator windings are of the order of 5 m A, a torque of 

 about 7 X 10 4 dyne-cm/deg is required. 1 In coupled synchro devices, 

 Fig. (1-2)43, a torque of 3 to 7 x 10 3 dyne-cm is required for every 

 degree difference in the position of the two rotors. 



The output voltage (peak value) of a synchro is usually about 15 to 



1 W.F. Goodell,inJohnF. Blackburn (ed.), "Components Handbook," M.I.T. 

 Radiation Laboratory Series, vol. 17, p. 328, McGraw-Hill Book Company, Inc., 

 New York, 1949. 



Fig. (1-2)43. Two synchro trans- 

 ducers acting as input and output 

 transducers. 



