Ratiometric vs. Phase Method Decoder
The ratiometric converters can track the shaft movements faster and can be mounted at a greater distance from resolvers as compared to phase method decoders.  They are also more immune to electrical noise and variations of voltage, frequency, temperature, etc.  Due to the more complex circuitry involved, the ratiometric converters are usually more expensive than phase method decoders.  In general, for more reliable operations, the ratiometric converter should be used.  In some applications, where wiring run is short and well shielded, system speed is slow or slow reacting outputs like electromechanical relays are used and the installation is relatively free of electrical noise, the phase method decoder may be considered for a cost effective design.

Built-in vs. Remote Decoder
Usually, resolver-to-digital decoders are housed in a separate enclosure, but resolvers with built-in decoders are also available.  The units with decoder circuitry packaged inside a resolver-housing combine the ruggedness of a resolver with simplicity of an optical encoder.  However, due to the electronics present in the same housing, the operating temperature range is considerably reduced as compared to a resolver with separate decoder.

The foregoing discussions is helpful in determining as to what type of transducer will be suitable for a particular application.  but before one can finalize a transducer selection, one needs to obtain additional mechanical and electrical requirements of the system.  Mechanical parameters to be determined are housing size, shaft size and loading requirements, mounting style, NEMA or explosion proof rating needed and system resolution.  Electrical requirements are the power supply voltage and current, output type (TTL, CMOS, sinking, sourcing, etc).  Analog or Digital outputs, output format (BCD, Binary, or Grey) etc.