62 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 1 



50 per cent lower than the input voltage and is shifted in phase 

 against the input voltage because of leakage inductance. The sensi- 

 tivity varies widely for different synchros from several hundred 

 millivolts to the order of 1.5 volts/deg of rotation (in the zero degree 

 position), and the accuracy varies for different synchros from ^0.1 

 to about 7°. The error also depends upon the rotor position and is a 

 maximum, for the three-coil synchro, at 60°. Synchros will operate 

 at velocities up to 1,200 rpm. 



Synchros are generally rugged transducers; they are little affected 

 by temperature in the range from — 55 to +95°C or by humidity up 

 to 95 per cent. Special differential synchro systems can be used to 

 form the sum or the difference of two or more angular displacements. 

 Synchros with two perpendicular winding systems furnishing an out- 

 put in the form of two orthogonal components (sine and cosine of the 

 displacement angle) are frequently referred to as resolvers. A circuit 

 for the use of a three-coil synchro as a resolver is described by Berger 

 and MacNichol. 1 



A modification of the synchro system, the Magnesyn, is shown in 

 Fig. (1-2)44. It consists of a toroidal coil wound on a core of high- 

 permeability and low-saturation field strength, such as Permalloy. 

 A permanent magnet in the form of a circular disk is mounted in the 

 center of the toroid and coaxial with it. The disk can be rotated 

 around the pivot point P. Two magnetic fields are induced in the 

 Permalloy core. The permanent magnet causes a constant ("d-c") 

 magnetic field which is sufficient to saturate the core. An a-c current 

 of the frequency/ fed into the toroid windings causes a magnetic a-c 

 field. The two fields are superimposed in parallel on one-half the 

 toroid and in opposition on the other half. The net effect is the induc- 

 tion of a voltage of twice the a-c frequency alternatingly occurring in 

 one or the other half of the toroid windings. The coil is tapped at 

 three places; the voltage induced between two taps is 



e = V sin 47rft cos d 



where is the angle between the north-south direction of the mag- 

 netic disk and the center of the coil. The operation is analogous to 

 that of a synchro. Commercial Magnesyns require only a few watts of 

 power and are accurate to about ^0.25°. 



/. Induction Systems. Transducer systems of the induction type 

 consist essentially of a coil with n turns in a magnetic field, as shown 



1 F. B. Berger and E. F. MacNichol, in Britton Chance, F. C. Williams, V. W. 

 Hughes, D. Sayre, and E. F. MacNichol (eds.), "Waveforms," M.I.T. Radiation 

 Laboratory Series, vol. 19, sec. 12.7, p. 444, McGraw-Hill Book Company, Inc., 

 New York, 1949. 



