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"Capacitive" Encoder
« on: August 18, 2008, 07:30:05 PM »
 :)
Anyone here have any experience with Capacitive encoders ?
Thanks for any input,
RC
« Last Edit: August 18, 2008, 08:22:03 PM by Overloaded »

Offline Kristin D

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Re: "Capacitive" Encoder
« Reply #1 on: August 18, 2008, 09:08:16 PM »
Can's see why they would not work well, provided they can take the abuse and have sturdy construction. Where or who is making them?

Kristin

Offline RICH

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Re: "Capacitive" Encoder
« Reply #2 on: August 18, 2008, 10:17:40 PM »
RC,
Never heard of them. I wonder what frequency is being used and the amount of RF generated. Also the units sensitivty to interference from other devices. What kind of enviroment and what applications are they recomended for?
Just some gut reaction's to a new device. Bottom line question is ....what are the short comings if any?
RICH
Re: "Capacitive" Encoder
« Reply #3 on: August 18, 2008, 11:27:47 PM »
Thanks Guys for the responses.
Here is a clip from the tutorial found here:
http://dkc1.digikey.com/us/en/tod/CUI/AMTEncoders_NoAudio/AMTEncoders_NoAudio.html
It clearly says for DC motors and I can only assume that they are quadrature. No mention of an index, not necessary for what I need anyway.
Look it over and tell me what you think.
I might order 2 tomorrow. $30 ea. and $7 for a cable with matching plug....Worth a try...
Check out the dip switch for selecting the resolution....pretty neat.

Thanks again,
RC

And here is one interesting note pertaining to steppers, so it does mention an index.
RC
« Last Edit: August 19, 2008, 12:09:12 AM by Overloaded »
Re: "Capacitive" Encoder
« Reply #4 on: August 19, 2008, 12:12:29 AM »

A capacitive position encoder which provides a digital output indication of the relative position between two plates. One of the plates includes first and second conductive input areas which are separated by a gap having the shape corresponding to a square wave. The second plate includes a number of rectangular output pads whose length is equal to one-half of the wavelength of the square wave. The pads are separated from one another by an integral fraction of the wavelength. Periodic input signals which are the inverse of one another are applied to the input areas and are capacitively coupled to the output pads. When the degree of overlap between an output pad and the input areas is equal, a null signal will be generated. Each pad will provide a null signal corresponding to a different position of the plates.
Ed VanEss
Re: "Capacitive" Encoder
« Reply #5 on: August 19, 2008, 12:23:30 AM »
Very interesting....GOOD stuff.
It's easy to see this working in a linear scale....like the digital caliper.
Thanks Ed,
RC

Offline Sam

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Re: "Capacitive" Encoder
« Reply #6 on: August 19, 2008, 04:15:28 PM »
One potential downfall that comes to mind (since were comparing them to calipers) is the ability to function at high speed. Now obviously, this is not a problem on calipers, and one would/should assume a motor encoder would have definitely addressed this. I would at least look into it before making a purchase, though.
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."

Offline Kristin D

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Re: "Capacitive" Encoder
« Reply #7 on: August 19, 2008, 04:55:40 PM »
The data sheet lists the number of ppr and rpm as :
Max RPM Resolutions
7500 RPM 2048, 1000, 800, 384 (plus res. from 15k and 30k RPM)
15000RPM 1024, 500, 400, 192 (plus res. from 30k RPM)
30000RPM 512, 250, 200, 96; 256,125, 100, 48

Although I have to wonder how those plastic hubs stand up to 30000 RPM.

Kristin

Offline RICH

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Re: "Capacitive" Encoder
« Reply #8 on: August 19, 2008, 05:28:49 PM »
RC
The idea of selectable resolution is kind of neat. Seems like easy installation. I am still a little concerned on operabilty from an RF / electrical field standpoint. Located any where near a a device which generates white noise, ie; like a motor or variable speed drive.  But you don't know until you try it out.  Wise man once said......one @30 to try is better than two in the drawer .........
 :) RICH

 
Re: "Capacitive" Encoder
« Reply #9 on: August 19, 2008, 06:21:59 PM »
Sam, That was one of my suspitions as well. I saw the data sheet too, thanks KD.
Rich, the cables ARE sheilded, hope that takes care of it.
We'll soon see, I have one on the way.
Thanks again All,
RC