Encoders - inexpensive

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01 Oct 2011 19:33 #13588 by centaur
Hi all - I just discovered a new inexpensive encoder. Let it be known that I am in no way associated with the company which makes them. I have been using the HEDS series from Avago and recently a new product appeared in Machine Design magazine which piqued my interest and might be usefull to EMC'ers. The encoders use a capacitive technology as opposed to LEDs as in the HEDS. They are available from Digikey for $26 in unit quantities. Here is the link to the manufacturers site:
www.amtencoder.com/
An interesting feature is that they are dipswitch programmable for different CPR's and with capacitive technology they do not exhibit the aging characteristics typical of optical technology. The data sheet indicates that accuracy is every bit as good as the HEDS series. They also come with a bucket load of adapters for various shaft sizes.
Have fun

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06 Oct 2011 04:11 #13696 by jmelson
Replied by jmelson on topic Re:Encoders - inexpensive
centaur wrote:

Hi all - I just discovered a new inexpensive encoder. Let it be known that I am in no way associated with the company which makes them. I have been using the HEDS series from Avago and recently a new product appeared in Machine Design magazine which piqued my interest and might be usefull to EMC'ers. The encoders use a capacitive technology as opposed to LEDs as in the HEDS. They are available from Digikey for $26 in unit quantities. Here is the link to the manufacturers site:
www.amtencoder.com/
An interesting feature is that they are dipswitch programmable for different CPR's and with capacitive technology they do not exhibit the aging characteristics typical of optical technology. The data sheet indicates that accuracy is every bit as good as the HEDS series. They also come with a bucket load of adapters for various shaft sizes.
Have fun

Yup, these encoders have a catastrophic flaw. They need an interpolator to increase the basic
resolution of the sensor. This interpolator has to respond to position, velocity and acceleration.
It handles the first two well, but badly lags on acceleration. See
pico-systems.com/images/compare_encoders.png
The red trace is velocity of an old HP encoder, the white trace is the CUI encoder velocity.
These encoders were mounted on opposite ends of the same motor. It is clear the CUI
encoder is slow to respond to velocity changes, and then has to overshoot on velocity
for the position (not shown) to catch up. This is a HORRIBLE situation for a servo loop,
when the apparent velocity of the motor is always lagging the true movement. You can see that
sometimes the velocity lags by 3 - 5 ms!

Jon
The following user(s) said Thank You: amaldo0

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06 Oct 2011 13:49 #13705 by centaur
Replied by centaur on topic Re:Encoders - inexpensive
Thanks Jon - that's really an eye opener! I am going to send this to the people at CUI and see if they respond and how they respond. I also am now curious as to what is the native resolution of their encoder and what they have in mind for applications.
Ray

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