Factors to be
considered for Selection
of Position Transducers
For an efficient control system,
the right selection of a position transducer is as important as the
signal processing itself. Here are some of the features and
trade-off to be considered to match the position transducer to your
application.
Optical Encoder vs.
Resolver
This decision is primarily based on the operating environment.
The environmental integrity of a brushless resolver is
unchallenged. Being simple rotary transformers, the resolvers can
take much more abuse than optical encoders and exhibit no significant
wear or aging. Especially, if the operating temperature is below
freezing or above 150º F, there is no other choice, but to go for
resolvers. Operating temperature range of resolvers is typically
between -67º F to +248º F. In extremely hostile environment such
as continuous mechanical shock and vibrations, humidity, oil mist,
coolants and solvents, resolver is the best choice
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Incremental vs. Absolute
Can you afford to lose position in case of power failure? If the
answer is no, then you must use an absolute encoder. An
incremental encoder simply generates pulses proportional to the
position, whereas an absolute encoder generates a unique code for each
position. After a power outage, with an absolute encoder, the
machine operation will pick up from where it had left off. In an
incremental encoder the pulses generated are counted in a counter and at
power loss it will lose the count and consequently you will have to home
the machine before you can start the operation. Also, an
incremental encoder is generally more susceptible to electrical
noise. The absolute encoders are more expensive than the
incremental encoders are. Therefore, a price/feature trade-off may
be worth considering.
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