A Synchro and Resolver to Digital Converter is a special device for converting the analog signals from Synchros and Resolvers to digital binary values, which can be read by a digital processing system. Synchros and Resolvers are special types of transformers that have a rotating primary coil and a number of fixed stator coils. If an AC signal is applied to the primary coil, a current is induced in the secondary coils that relate to the phase of the rotation of the primary about the fixed secondaries. A Synchro has three or more outputs that relate to the phase position of the primary rotor. A Resolver is similar to a Synchro except it has secondary windings that are at right angles to each other and output levels that can be directly related to a Cartesian coordinate of a vector rotating around a unit circle. Alternatively, some resolvers can output other special purpose trigonometric functions.

 

These special analog to digital converters (ADCs) usually have at least (and typically) two analog inputs from the secondary windings. They will also typically have an internal reference oscillator that is used by the converter in its tracking loop and output from excitation outputs to go to the primary winding circuit on the stator. The tracking loop of this ADC continually tracks the position of the resolver. This can include the special Variable Reluctance Resolvers that have the primary winding vary in distance to the stator – creating a change in amplitude of the coupled signal. 

 

Synchro and Resolver ADCs have good resolution accuracy,  good phase accuracy over time specification (expressed typically in arc minutes) and maximum rotations per second tracking rate. Many of these devices integrate an incremental encoder output generating a quadrature encoded digital output in the same way that other encoders do. They can detect faults, such as a loss of signal. They can also have digital serial or parallel interfaces to the digital processing circuit.

 

These special purpose ADCs are found in service motor control, electric vehicles, antenna and mast control systems, and automotive motion sensing and control systems.