7i77 encoder split to amp and servo

blazini36,

Thanks for pointing out the Encoder Y! Of course Mesa makes a solution for everything!

PCW, will the encoder y board offer isolation? Not sharing the grounds? Could I read in differential from the encoder and split(Y) to drive single ended without lowering the voltage swing? Sorry, I could not find the product doc on your site. Do you have a link?

I need to further scope the encoder as the A and B channels look flaky on halscope. I have an inconsistent pulse width both in mode1 and 0.
I also enabled  quad-error-enable true but it didn't trigger. I assume in 2.8 version, axis gui would display a warning? Or does the error checking need further hal connection?

The EncY is not isolated by will function as a re-driver
to lower loads from termination. We have considered an
isolated version but have not made it yet.

You have to monitor the encoder error bit youself
and it requires using 2.9 or later as there were errors
in handling errors in multiple channels before that.

OT-CNC wrote:

blazini36,

Thanks for pointing out the Encoder Y! Of course Mesa makes a solution for everything!

PCW, will the encoder y board offer isolation? Not sharing the grounds? Could I read in differential from the encoder and split(Y) to drive single ended without lowering the voltage swing? Sorry, I could not find the product doc on your site. Do you have a link?

I need to further scope the encoder as the A and B channels look flaky on halscope. I have an inconsistent pulse width both in mode1 and 0.
I also enabled  quad-error-enable true but it didn't trigger. I assume in 2.8 version, axis gui would display a warning? Or does the error checking need further hal connection?
 

I don't fully understand your setup but i've never considered sharing a single encoder between 2 devices as a particularly good idea, it's probably espescially bad if one is single ended as the load on the inverting and non-inverting outputs will be different besides however it affects RS422 termination.

If you actually need isolation on the encoder you might try looking for a magnetic or "digital" isolator. I think they'd be fast enough to handle differential inputs directly, pd is <8ns. I whipped up a few in case I ever needed them, don't think I've bothered to test them for that. I use the same family of isolator for a bunch of serial stuff since they work as simple 3v-5v level shifters as well.

 

I am using split encoders on a plasma machine, with no isolation and no add on boards, but that implies having both sides at the same potential, failure to have them at the same potential will end up badly.
Do not take this as advice to do so, just as a "can be done" thing.
forum.linuxcnc.org/show-your-stuff/47357...ines?start=10#257711

Well you can do alot of things, doesn't mean it's always a good idea. Somebody just posted about those CUI encoders that according to the datasheet don't even drive enough current to operate the receivers on a Mesa card according it it's manual.....maybe it'll work, probably not a good idea. When you start having problems you have to ask "what are the things I did that were not good idea?" If it just works, why bother asking?

I have no idea what kinda drives or encoders we're even talking about here, just making suggestions specific to the questions that were asked.

PCW,
Nice board. 
I lack some fundamental electrical knowledge. In general, on a line driver type differential encoder, if the receiver is only single ended (my drive), it was my understanding that one can still read in just the A and B channels. If so, do /A and /B need further termination or can they be left floating/unconnected? 
Or is it better to just get a single ended encoder if the receiver is single ended? 

Tommylight,
I have a split setup on a lathe spindle that works very well with rigid tapping / threading and css. I'm reading in differential on both ends one to encoder card on vfd and the other to 7i77 for velocity control, so not trying something odd like current setup.

Current problem is trying to get a 4th axis indexer working. The drive (AMC ab30a200) only reads in single ended encoder for velocity feedback. I'm not sure why a new analog drive would have limited encoder channels in addition there is no encoder out from the drive to linuxcnc.
I think most of the digital drives have the additional encoder output. Unless I'm missing something, I'm forced to split it if I want encoder feedback.
One option is I can use current mode in the drive and read in the encoder on 7i77 only. Unfortunately  I can't get good shaft lock in current mode.
Best option so far is hall velocity feedback in the drive and encoder to 7i77. Shaft lock is good but runs somewhat rough. Suspecting noise and bad encoder signals. This drive is not isolated. That was an extra option.