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Rotary encoder accuracy - mine doesn't seem very good
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Corporate666:
I picked up one of those cheap Chinese incremental rotary encoders from Amazon to use for measuring linear speed... I'm timing the gap between pulses to come up with a speed reading.  I am seeing a variance of 15%, even when I turn the encoder at a very precise rate.  I've attached a wheel to the encoder and mounted it to the table of my (pro, not hobbyist) CNC machine, and hooked up the encoder output to my oscilloscope and I see a variance of +/- 15% in pulse width (and time between pulses) as the encoder turns.  It isn't random... it seems to cycle from -15% to +15% and back, which seems to suggest slop in manufacturing.

I'm wondering if this is normal for these cheap Chinese encoders or is this possibly just a bum unit?  I don't want to buy a handful more if they could all be expected to be equally bad.  What about the $50-100 range encoders from the likes of Grayhill, Copal, and Honeywell - should I expect more accuracy from those units over the Chinese encoders from Amazon?

Thanks for any input.
ataradov:
What specific encoder you are talking about? I've used this type https://www.ebay.com/itm/DC5V-24V-360P-R-Encoder-Incremental-Rotary-360-Pulses-R-AB-2-Phase-6mm-Shaft/141656690772 and a few units I've got were fine. But this was many years ago, so they may have optimized something in the design.
timpattinson:
Is it inside the specified nonlinearity?
Corporate666:

--- Quote from: ataradov on March 06, 2019, 07:23:24 am ---What specific encoder you are talking about? I've used this type https://www.ebay.com/itm/DC5V-24V-360P-R-Encoder-Incremental-Rotary-360-Pulses-R-AB-2-Phase-6mm-Shaft/141656690772 and a few units I've got were fine. But this was many years ago, so they may have optimized something in the design.

--- End quote ---

The one I am using at the moment is this one:

https://www.amazon.com/gp/product/B00Y9KDDCY

Corporate666:

--- Quote from: timpattinson on March 06, 2019, 08:36:54 am ---Is it inside the specified nonlinearity?

--- End quote ---

I haven't seen any manufacturer of optical incremental encoders list a spec for non-linearity in their datasheets, and certainly not these Chinese units, so there's no way to know if it's in-spec or not.  I assume it's just crap quality... so was hoping others could speak to their experiences with them.

This is the OEM:

http://www.china-encoder.com/

and the encoder:

http://www.china-encoder.com/product_detail/productId=24.html

it seems to me that a variance of +/- 15% for an optical incremental rotary encoder is massive and shouldn't be the norm... but maybe I am expecting too much.  Just wondering if I got a bad unit, or if it's par for the course, or if I should expect a $50 or $100 encoder from a name brand to be better (and if so, how much better), or how much I need to spend to get 1% or so?
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