Design, Performance and Application of the Vernier Resolver

The precise measurement of an angle is a basic operation in many technical fields. T h e observation of stars, mapping of land, machining in the factory are all operations which require angle measurements. Of course, an angle can be measured by reading a calibrated dial. However, in automatically controlled operations t h e angular position of a s h a f t has to be sensed electrically. The instrument which performs the conversion from a mechanical angle to an electrical output is called an angle transducer. One commonly used angle transducer is the synchro resolver. Basically this is a variable coupling transformer with one primary winding and two o u t p u t windings displaced 90 degrees from each other. T h e variable electrical coupling is accomplished by placing the primary * T h e Vernier Resolver was developed under the sponsorship of the Wright Air Development Center. 1487 1488 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 winding on the rotor and the secondary windings on the stator or vice versa. T h e primary winding is excited from an alternating voltage source of, say, 400 cycles per second. T h e amplitudes of the induced secondary voltages of the synchro resolver are ideally proportional to the sine and cosine of the rotor orientation. These two induced, amplitude modulated voltages are the resolver output. T h e accuracy of commercially available synchros is, at best, three minutes of arc. Certainly, this accuracy is sufficient for many applications. In the machining of precision parts and in field applications involving the measurement of elevation and azimuth of distant targets, however, accuracies down to 10 seconds of arc are required.