Specifications

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 tem-
perature is below freezing or above 150 °F, there is no other
choice, but to go for resolvers. Operating temperature range of
resolvers is typically between -67 °F to +248 °F. In extremely
hostile environment such as continuous mechanical shock and
vibrations, humidity, oil mist, coolants and solvents, resolver is
the best choice.
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 incre-
mental 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.
800-TEC-ENGR
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A-6
Position Transducers/Sensors
(Figure 4)