# Oscilloscope recommendations



## ecdez (Oct 22, 2014)

Never thought I would need one but my recent endeavors have precipitated a sudden requirement to have one.  Can anyone recommend a good, small, basic model?

I would try the used route but I have no way to determine if one is good or not, how would one tell that?


Suggestions are welcome.


If you're local and have one to loan, that would be great too )!


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## zmotorsports (Oct 22, 2014)

Depends on what you are using it for.  I have an OTC DSO for automotive work and it works great.  It is not color but is a two channel Digital Storage Oscilloscope.

About ten years ago I did have a Fluke color four-channel that I bought slightly used, it was like new condition though.  Thought I had a gem, and it was a very nice DSO, however, for automotive/motorcycle work it had too high of a sampling rate and was very difficult to read with any accuracy.  I was also just learning to use a DSO and wanted something a little more user friendly to learn on.

I was able to re-sell the Fluke and had enough to purchase a new OTC one with all the nice accessories for back-probing wires etc.


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## ecdez (Oct 22, 2014)

Hadn't considered that usage would be a determining factor or I would have mentioned that.  I thought they were all pretty much the same.


Seems I bought a lemon of a CNC mill and I need an oscilloscope to check the encoders for proper function.


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## Rbeckett (Oct 22, 2014)

I have a Beckman 2 channel that runs up to 10 KHz so it doesn;t sample too fast and it gives a good reliable steady trace when I want to look at a wave or frequency.  Nice little 2 channel that is still  pretty basic but it doesn't sound like you need an advanced instrument.  Look around you can find them on Ebay and craigs list all the time for about a 100 bucks,  And just buy it with a money back guarantee against DOA and fried machines. Look at the last calibration date and make sure it has a manual too.  There is a test procedure in the manual that is fairly easy to perform if I'm not mistaken, mine does.

Bob


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## Tony Wells (Oct 22, 2014)

Too bad you're not local to me. I have 3 scopes ready to go.


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## spaceman_spiff (Oct 22, 2014)

ecdez said:


> Hadn't considered that usage would be a determining factor or I would have mentioned that.  I thought they were all pretty much the same.
> 
> 
> Seems I bought a lemon of a CNC mill and I need an oscilloscope to check the encoders for proper function.



I'd recommend a digital scope for encoders. Buy used, and only from major brands, unless you want a headache as far as things not really working how you would expect. So Tektronix or Agilent, etc..

High resale value. You can basically buy them used for $700 and then sell it when you are done for the same price and lose only the 13% if you sell on ebay. Lose 0% if you sell on craigslist.

You may be able to get the job done with a multimeter if you are only checking basic phase and presence of signal for the encoders. If you need to watch for strange behavior that only appears at high speed then most likely you will need a digital scope, which is much better at capturing, storing, and displaying transients than an analog scope, which at best may have a storage phosphor setup of unknown reliability since anything like that is going to be 30+ years old.


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## jgedde (Oct 22, 2014)

As far as scopes for hobby/shop use, Rigol makes affordable scopes that are very good quality, have good graphics, and excellent performance.  We use them here at work too.

http://www.rigolna.com/products/digital-oscilloscopes/

John


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## rpmMan (Oct 22, 2014)

I have always been partial to fluke scope-meters.. if you can find a 192, 196 series for a decent price that is what I would get.. plus if you ever need to troubleshoot a vfd .. having a battery operated totally isolated scope is the safe way to proceed.. 

rich


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## JimDawson (Oct 22, 2014)

Here is the deal of the day for an oscilloscope.  http://www.frys.com/product/4279454?site=sr:SEARCH:MAIN_RSLT_PG


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## ecdez (Oct 22, 2014)

spaceman_spiff said:


> You may be able to get the job done with a multimeter if you are only checking basic phase and presence of signal for the encoders. If you need to watch for strange behavior that only appears at high speed then most likely you will need a digital scope, which is much better at capturing, storing, and displaying transients than an analog scope, which at best may have a storage phosphor setup of unknown reliability since anything like that is going to be 30+ years old.




This may be a good interim solution.  I think I fried my encoders but need to check them to see if I need to replace or not.  I have a good one I can use as a baseline.  I guess if I get no signal at all, they're toast.





rpmMan said:


> I have always been partial to fluke scope-meters.. if you can find a 192, 196 series for a decent price that is what I would get.. plus if you ever need to troubleshoot a vfd .. having a battery operated totally isolated scope is the safe way to proceed..
> 
> rich




I was checking those out, they are nice.






JimDawson said:


> Here is the deal of the day for an oscilloscope.  http://www.frys.com/product/4279454?site=sr:SEARCH:MAIN_RSLT_PG



WOW, can't argue with that!  Looks like everywhere else the prices are way higher. Wonder how they can offer them for that price.


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## spaceman_spiff (Oct 22, 2014)

ecdez said:


> This may be a good interim solution.  I think I fried my encoders but need to check them to see if I need to replace or not.  I have a good one I can use as a baseline.  I guess if I get no signal at all, they're toast.



Why not tell us about the specifics of your encoder issue?  Ive had to do quite a bit of encoder work and could probably help you get to the bottom of things fast. What is the make and model of the encoder? Pics and info please


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## JimDawson (Oct 22, 2014)

JimDawson said:


> Here is the deal of the day for an oscilloscope. http://www.frys.com/product/4279454?site=sr:SEARCH:MAIN_RSLT_PG





ecdez said:


> WOW, can't argue with that!  Looks like everywhere else the prices are way higher. Wonder how they can offer them for that price.



I did  bit more research, this scope is a discontinued item.  It looks like there is one available in the one of the Texas Fry's stores. 

Almost any 2 channel scope would  work.  Another option would be to take the encoders down to your local motor shop and have them checked out.  Any shop that works on servo motors could help you out.


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## ecdez (Oct 22, 2014)

The details about my CNC saga can be seen here but I doubt it's worth a complete read but it does set the stage and possibly make me look less stupid than the description below.  http://www.hobby-machinist.com/show...se-help-This-stopped-being-fun-a-few-days-ago


The mill I have has to go through a process when you first start it up to calibrate the axis.  Part of that process involves running each axis  (in order of Z, Y, X) to one of the limit switches.  Z axis is fine and as it goes through the process I can see the value changing on the screen.  When it goes to the next axis, Y, it moves but no values change on the screen and then I get a fault.  Checked all the connections and everythings fine so that leads me to believe it the encoder.  If you filter through the above thread you can see that my theories havn't worked out for the best with this thing.  I would rather check parts before I start replacing them so that lead me to an oscilloscope.


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## spaceman_spiff (Oct 22, 2014)

ecdez said:


> The details about my CNC saga can be seen here but I doubt it's worth a complete read but it does set the stage and possibly make me look less stupid than the description below.  http://www.hobby-machinist.com/show...se-help-This-stopped-being-fun-a-few-days-ago
> 
> 
> The mill I have has to go through a process when you first start it up to calibrate the axis.  Part of that process involves running each axis  (in order of Z, Y, X) to one of the limit switches.  Z axis is fine and as it goes through the process I can see the value changing on the screen.  When it goes to the next axis, Y, it moves but no values change on the screen and then I get a fault.  Checked all the connections and everythings fine so that leads me to believe it the encoder.  If you filter through the above thread you can see that my theories havn't worked out for the best with this thing.  I would rather check parts before I start replacing them so that lead me to an oscilloscope.



That process of homing using a switch then rotating until an index is found is pretty much the standard all VMC's use going back decades..its how my Japanese CNC mill works and how a Fadal 3016 works. 

I would definitely hold off on buying the oscilloscope until further notice. You can confirm encoder output in a gross sense by setting your multimeter to the Hz/Frequency measurement and measuring the encoder pulses at a known feedrate, and calculating what the frequency should be. I assume that encoder is a +5V with quadrature output and an index. 

Or you could try swapping encoders between X and Y axis and see if the problem follows the encoder. 

Does your mill use servomotors with encoder feedback to close the loop? If so, its unlikely there would be any control of the Y axis if the encoder was bad. What does the fault error say?

That thread is definitely TL;DR, but I skimmed through it..I would highly recommend dropping the idea of a retrofit or changing Hurco's design.  If you arent prepared to troubleshoot a problem like this, retrofitting is an order of magnitude more difficult and expensive.

So lets get down to basics, the homing problem.

I take it at this time, the machine homes on all axis correctly, except Y axis?

Questions:

Can you feed the Y axis without homing (watch out, dont hit the physical stops)?

And if so, does it move smoothly and at the selected feedrate?


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## daveyscrap (Oct 22, 2014)

The other option would be a simple logic probe from radio shack . They are as easy to use as a test light.


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## JimDawson (Oct 22, 2014)

spaceman_spiff, you might want to look through the post referenced above.  This is just another chapter in a continuing saga.  The mill has run fine on some occasions, after some major troubleshooting.  The latest failure seems to be an encoder issue.


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## ecdez (Oct 22, 2014)

JimDawson said:


> Almost any 2 channel scope would  work.  Another option would be to take the encoders down to your local motor shop and have them checked out.  Any shop that works on servo motors could help you out.



I appreciate the suggestion but I'm just a little stubborn in that regard.  I've never been the guy to take my stuff somewhere to have someone else check it out or work on it.  By the time I pay someone to do that I could have bought (or at least partially paid for), a new tool for me to do it myself.  Not to mention the gained ability to trouble shoot it next time.  I learned my first lesson in that a long time ago and never forgot it.

I'm not defeated yet Jim!  )


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## ecdez (Oct 22, 2014)

X2 on what Jim said.  When it works, it's a great machine.  Hogs through material like a beast.  It took me a while and a lot of troubleshooting to get to that point but get there we did.

I believe the error says something about not detecting a marker or something like that but the more defining clue is the readout does not read movement like the Z axis does.

Until the initial cycle process is complete, no other controls work at all.  Y axis is the second with Z being the first and Z cycles fine.


A retro is definitely on the radar but I'd like it to limp along until I'm ready to dive in.  If possible, I'd like for it to pay for the parts to do the retro.  I'm constantly passing on work while it's down. This is a side hustle and I'm a single income household with 4 kids so extra money is non-existent.  If I can get a month or two of work out of it that would give me the necessary funds to buy all the parts I need for the retro.


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## ecdez (Oct 24, 2014)

Finally got all the encoders off and ran some basic tests.


Basically just checked the voltage coming out of each lead as I turned the shaft very slowly.  Used a small 12v power supply.


Z aixs - known good
A - fluctuates between 14v and 0
B - fluctuates between 14v and 0
Z - fluctuates between 115mV and 0


Y aixs
A - fluctuates between 13.25v znd 12.5v
B - fluctuates between 12.5v and 13v
Z - fluctuates between 10.3v and 10.35v


Xaixs
A - fluctuates between 14v and 0
B - fluctuates between 14v and 0
Z - only get a reading of 10mV - no fluctuation


I know this is not as accurate a test as an oscilloscope would offer but I know now there is a different reading between the known good one and the others.  There's definitely something fishy there.  I have found a scope locally that I told I could borrow so I'm gonna make him up on that.


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## JimDawson (Oct 24, 2014)

ecdez said:


> Finally got all the encoders off and ran some basic tests.
> 
> 
> Basically just checked the voltage coming out of each lead as I turned the shaft very slowly.  Used a small 12v power supply.
> ...




That is actually a pretty good test.  It looks like it proved that the Y axis encoder is not working. 

Just a side note, if you didn't already know, the Z (sometimes labeled "I") output only pulses once per revolution, this is the Index pulse, normally only used in homing functions.

It will be interesting so see what the O-scope trace looks like.


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## countryguy (Oct 24, 2014)

Well I for one am bummed out on the fry's deal being in-store only!   My oscope is a. Heath kit 20mhz I built myself in high school. Lol.   And I still use it but have been keeping an eye out.  The price was a nice find Jim!


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## Smithdoor (Oct 25, 2014)

You use your pc as a Oscilloscope using the sound card and a program/app free off the internet
This works to about 40K there some cards/USB that will go a lot higher

Dave


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## Jawn (Oct 25, 2014)

countryguy said:


> Well I for one am bummed out on the fry's deal being in-store only!   My oscope is a. Heath kit 20mhz I built myself in high school. Lol.   And I still use it but have been keeping an eye out.  The price was a nice find Jim!


You ain't the only one. $2k+ scope for $300? Yes please. Anybody that got one (in good working order) at that price basically stole it.


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## RWL (Nov 5, 2014)

I have no personal experience with oscilloscopes, but my EE son says that at the university where he works, the dept chair is pushing for each student to have a USB oscilloscope / lab in a box and get away from dedicated oscilloscopes in the dept.

http://www.digilentinc.com/Products...885eba255-F1A3E61D-5056-0201-027A0E6A23D07899


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## countryguy (Nov 5, 2014)

It has a slew of features!  Cool for $99 as my Student Son would be the owner.   5Mhz analog capacity on the Oscope.   thanks for the post.  Will keep that handy.  

 2-Channel Oscilloscope
• 2-Channel Waveform Generator
• 16-Channel Logic Analyzer
• 16-Channel Digital Pattern Generator
• ±5VDC Power Supplies 
• Spectrum Analyzer
• Network Analyzer
• Voltmeter
• Digital I/O


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## pdentrem (Nov 5, 2014)

countryguy said:


> My oscope is a. Heath kit 20mhz I built myself in high school. Lol.   And I still use it but have been keeping an eye out.  The price was a nice find Jim!




I do not know if it still works! Been sitting for years.
Pierre


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## xalky (Nov 5, 2014)

RWL said:


> I have no personal experience with oscilloscopes, but my EE son says that at the university where he works, the dept chair is pushing for each student to have a USB oscilloscope / lab in a box and get away from dedicated oscilloscopes in the dept.
> 
> http://www.digilentinc.com/Products...885eba255-F1A3E61D-5056-0201-027A0E6A23D07899


That's awesome! A powerful tool in a small package. I've been looking for a decent scope at a reasonable price, this looks like just the ticket.


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