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Help With Choosing Magnetic Scales
#1
Hey guys,  

I have a Launchpad more or less up and running with cheapo Shahe scales, but for various reasons I feel like upgrading to magnetic scales.

As I live in China, I can get some slightly cheaper than overseas, but I have run into an issue when choosing between two specific models.They are both from SPM. One is MR50 and the other is called MR500. Now, I need to know if the signals will work for the quadrature controller but I can't dust up any data sheets...:-(
Yuriy says this in one of the articles:
"Refer to your specific scale's manual to ensure that it outputs either single-ended or differential quadrature signal."

One seller of these scales told me (through Google Translate) that the cheaper MR50 has a TTL signal and "single wave" whereas the more expensive MR500 has RS422 and "double wave".

I wonder if both of them will work? My gut feeling is yes, but would like to have a bit more certainty.
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#2
If it were me, I would go with the RS422 scales for the noise immunity. From his pictures it looks like Yuriy used the MR500.
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#3
(10-11-2018, 03:59 PM)Briney Eye Wrote: If it were me, I would go with the RS422 scales for the noise immunity.  From his pictures it looks like Yuriy used the MR500.

Yes, I noticed he used that one, too. But I thought it could just have been an availability issue.
Anyways, I wrote SPM and they replied the following:

MR500 is differential signal (A ;  /A  ; B ; /B ; Z ;/Z)
 
MR50 just has A B and without Z signal(reference point)

So, perhaps that Z signal is what makes the noise cancellation possible?
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#4
(10-12-2018, 04:13 AM)GeckoSub Wrote:
(10-11-2018, 03:59 PM)Briney Eye Wrote: If it were me, I would go with the RS422 scales for the noise immunity.  From his pictures it looks like Yuriy used the MR500.

Yes, I noticed he used that one, too. But I thought it could just have been an availability issue.
Anyways, I wrote SPM and they replied the following:

MR500 is differential signal (A ;  /A  ; B ; /B ; Z ;/Z)
 
MR50 just has A B and without Z signal(reference point)

So, perhaps that Z signal is what makes the noise  cancellation possible?

No, Z is an index pulse that is output once per encoder revolution.  Useful in some applications, like establishing a precise home position.  The noise cancellation is provided by the differential signal.  The receiver only cares about the difference between A and /A, within some common mode range.  Since induced noise tends to appear on both lines, their simultaneous wiggling cancels out.
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#5
(10-12-2018, 02:44 PM)Briney Eye Wrote:
(10-12-2018, 04:13 AM)GeckoSub Wrote:
(10-11-2018, 03:59 PM)Briney Eye Wrote: If it were me, I would go with the RS422 scales for the noise immunity.  From his pictures it looks like Yuriy used the MR500.

Yes, I noticed he used that one, too. But I thought it could just have been an availability issue.
Anyways, I wrote SPM and they replied the following:

MR500 is differential signal (A ;  /A  ; B ; /B ; Z ;/Z)
 
MR50 just has A B and without Z signal(reference point)

So, perhaps that Z signal is what makes the noise  cancellation possible?

No, Z is an index pulse that is output once per encoder revolution.  Useful in some applications, like establishing a precise home position.  The noise cancellation is provided by the differential signal.  The receiver only cares about the difference between A and /A, within some common mode range.  Since induced noise tends to appear on both lines, their simultaneous wiggling cancels out.

Got it, like in audio XLR cablesSmile
So, the MR50 doesn't have the "double" A and B signal. Just a single one for each of them. I might go for the MR500 then as one of the reasons I never grew super fond of the Shahe scales were that they sometimes lost their counts out of nowhere. I even had the external, backup battery mod, so perhaps it was noise related (though I also did the capacitor fix). The magnetic scales are way overkill as I am on a tiny mini lathe but sometimes it's ok to treat yourself to nice stuff;-)
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