VERNIER RESOLVER 



1497 



IV. APPLICATION 



In its application, the vernier resolver is usually directly coupled to a 

 standard resolver or some other coarse angle transducer. Such a system 

 which represents a ^'ariable, in this case the shaft angle, in two scales, 

 coarse and fine, will be called a vernier system. 



The following sections describe applications using the vernier resolver 

 in an encoder, a follow-up system and an angle-reading system. 



4.1 Vernier Angle Encoder 



A vernier angle encoder converts a shaft angle into a pair of digital 

 numbers, one being the coarse and the other being the vernier number. 

 This type of encoder can be built by mechanically coupling a standard 

 resolver directly to a vernier resolver. The outputs of the two resolvers, 

 after encoding, represent the coarse and the vernier number. 



The output of a resolver may be encoded, for instance, by the following 

 method. The primary winding of the resolver is excited from an a-c 

 source of, say, 400 cycles per second. The two induced secondary volt- 

 ages are in phase with each other. Their amplitudes are proportional to 

 the cosine and sine of the electrical rotor angle, de . 



These two amplitude modulated voltages are combined by means of 

 two phase-shifting networks into two phase-modulated voltages. One net- 

 work first advances the sine voltage by 90° and then adds it to the cosine 

 voltage. The other network performs the same addition after retarding 

 the sine voltage by 90°. The result is two constant amplitude voltages 

 with relative phase shift of twice the electrical rotor angle. The time in- 

 terval between the respective zero crossings of these two voltages is con- 



_Y/. 



PHASE 

 MOTOR 



Fig. 9 — Resolver servo system. 



