Encoder or Resolver? You Make the Call

Here's the reader question we published in the October issue. "We need to measure motor speed in our dry food packaging machines to close the loop for more precise control.

We've narrowed our choices to either an encoder or a resolver, but we're having trouble deciding which is best. What are the advantages and drawbacks of each technology?"

Sounds like we need a few of you to drop some of your experience on this subject. Betcha they were using open loop step and it's no longer good enough. Give this reader a hand right now via "comments" link below or send us your comments, suggestions, or solutions at RealAnswers@putman.net. Please include your company, location and title in the response.

Have a problem you'd like to pose to the readers? Send it along, too.

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  • <p>In a perfect world you can't beat a resolver, the exacting control across time is unbeatable. Unfortunately things break and technicians become less &amp; less technically competent every day.</p> <p>My opinion (as a tech who maintained both technologies for more than 20 years) encoders are easier to setup and maintain, especially in high speed production applications.</p> <p>I know I will catch flak for this one, but as of a couple of years ago it was just as, or even more important to consider the cost and complexity of the motion control system that supported the resolver or encoder. Resolvers were more expensive from a total control point of view.</p> <p>I could teach a guy with a multimeter how to maintain an encoder controlled system. How many shop floor tech's these days even know how to read an oscilloscope to setup and maintain a resolver?</p> <p>If the customer has lots of money and a technically competent maintenance team, go for the resolver, if not, go for the encoders EVERY TIME.</p> <p>Scott</p>


  • <p>Resolvers are inherently more rugged than encoders, and less susceptible to electrical noise. Those are the only advantages. The disadvatages are that a resolver is an analog device, so you'll have an analog-to-digital conversion somewhere along the line. Not a big deal, but virtually every controller can take an encoder input, as opposed to resolver inputs being somewhat rare. Not all resolvers are built the same way, meaning you have to match your resolver to your input fairly carefully. Though resolvers theoretically have an infinite resolution, in practice they are roughly equivalent to a thousand or so ppr encoders. Resolvers are rarer and therefor more difficult to obtain.</p> <p>Encoders have a glass disk that can shatter. There are also some electronics that are susceptible to heat and possibly vibration. Having said that, encoders are used all over the place, so it's not like they're super fragile. You can have encoders with VERY high resolution, but around a thousand ppr is common. Lots of places have encoders in stock, though the wide variety sometimes means that you can accidentally pick an oddball, so work with your vendor and make sure you pick something common.</p> <p>I recently went through this same issue and ended up picking an encoder.</p> <p>I disagree with the previous comment about maintenance. There is NO maintenance on either one. If there's a problem, replace it, just like any other sensor. If you find yourself getting out a multi-meter or o-scope to check a </p>


  • <p>Here's an interesting news story on the state of the North American market for optical encoders and other linear displacement sensors - <a href="http://www.controldesign.com/industrynews/2007/040.html">http://www.controldesign.com/industrynews/2007/040.html</a></p>


  • <p>My hands down favorite is an encoder. As mentioned, before, they are simpler digital devices. 1000 pulses per revolution resolution should be sufficient for most applications. Many CNC machine tools servo systems use them for both positioning and for speed and direction feedback. They are much more common.</p>


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