Specifications

Single-Turn vs. Multi-Turn
In a single-turn encoder, the encoder shaft makes one revolu-
tion for one complete cycle of machine operation, where as in
a multi-turn application, the encoder shaft makes more than
one revolutions to complete one machine cycle. Angular rota-
tion of a crankshaft in a punch press or rotary indexing table
are typical examples of single-turn applications. In linear posi-
tioning, where the encoder shaft makes several turns to com-
plete total travel, a multi-turn encoder will be required.
Absolute multi-turn encoders and resolvers are available with
various built-in gear ratios. Incremental encoders can be used
both in single-turn and multi-turn applications.
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 opera-
tion, the ratiometric converter should be used. In some appli-
cations, 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 avail-
able. 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 electron-
ics present in the same housing, the operating temperature
range is considerably reduced as compared to a resolver with
separate decoder.
The foregoing discussion 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 cur-
rent, output type (TTL, CMOS, sinking, sourcing, etc), Analog
or Digital outputs, output format (BCD, Binary, or Grey) etc.
A-7
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Position Transducers/Sensors
SECTION
A