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Electronics & Test

Design Decisions: Choosing a Rotary Encoder

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Amclaussen
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Platinum
Sometimes resolution is not important, but other things are.
Amclaussen   1/4/2012 12:09:48 PM
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We are using a RVDT to track the opening percentage of large Ball type valves used in Pipelines to monitor closing sequence and speed.  Here, resolution was not necessary, but reliability is of utmost importance; the RVDT is rugged and very reliable.  Amclaussen.

Alexander Wolfe
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Blogger
Re: Sometimes resolution is not important, but other things are.
Alexander Wolfe   1/4/2012 1:06:19 PM
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Positional accuracy seems like the key spec when choosing a rotary encoder, but what about MTBF? Does that come into play at all, especially considering that it's a part which gets a heavy and constant workout?

TJ McDermott
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Re: Sometimes resolution is not important, but other things are.
TJ McDermott   1/4/2012 10:18:18 PM
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Environmental protection is frequently a deciding factor in industrial environments.  Can it take being hosed down with high pressure, caustic solutions such as is found in food processing?  Can it resist coolant or oil?

GlennA
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Gold
resolver vs encoder
GlennA   1/6/2012 8:58:52 AM
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My experience with resolvers was with ABB industrial robots.  The first absolute positioning system I saw used 3 resolvers (IRB 90), followed by 2 (IRB 2000) and finally 1 resolver and a revolution counter (IRB 6400).  The feature I thought was most useful was it 'failed-safe'.  An axis with an encoder has to fail to show movement feed-back when commanded to move to detect a failure.  How far does tha axis move before the lack of position change feed-back causes a fault ?  With a resolver, a broken wire causes a failure during initialization.

Jack Rupert, PE
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Platinum
Re: Sometimes resolution is not important, but other things are.
Jack Rupert, PE   1/22/2012 2:34:50 PM
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Absolutely, Alex.  In my previous position, the MBTF was actually more important than linear accuracy.  It was so true that "others" demanded a spare as part of the standard BOM, rather than on the list of suggestions for our customers.  (It was useful too, when the mechanical system fail and destoyed the position sensor - which actually was working quite well).

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