Forums » Hardware » Probe calibration HOWTO

Thoralt
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  • Wrote 20 posts
  • Member since 8 Sep 14

-- update: see http://wiki.lab-nation.com/index.php/Calibrating_the_probes for a version of this post updated to the latest GUI --

Hi,

most makers might already know what I'm talking about, but since the SmartScope is likely to be used by electronics newbies, too, I want describe the probe calibration process.

The probes delivered with the SmartScope have a defined impedance which needs to be matched against the input impedance of the scope to get a flat frequency response (at least up to the maximum input frequency of the scope). Doing this is an easy process: Switch both of the probes to 10x mode and connect them to the AWG output.

Set the AWG to a square wave of approx. 500 Hz and click "Upload function". Next, scale both waveforms to 200 mV/div and 500 us/div to get a good overview of the waveforms. The following image shows the waveforms in case the impedance is totally wrong, one channel over compensated, the other under compensated:
uncompensated
Now use the little screwdriver tool provided with the probes to slowly turn the little screw inside the BNC connector of the cable until the waveform on the screen is as square as possible. If both channels look as shown below, you're done.
compensated

Christian Ehlers
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  • Wrote 49 posts
  • Member since 18 Sep 14

Maybe you could change your post to link to the images instead of showing them inline?

It's impossible to see all the text in Firefox because there is no vertical scroll bar.

Riemer
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  • Wrote 457 posts
  • Member since 20 Feb 14

strange.. are you saying there is no vertical scoll bar on firefox on this page?
here on chrome everything looks just fine. so let us know, as we might have a problem with browser compatibility

Christian Ehlers
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  • Wrote 49 posts
  • Member since 18 Sep 14

Yes... I actually had to add the images to adblock plus in order to read the text.

https://dl.dropboxusercontent.com/u/21323188/lab-nation.com_forumbug.png

Jasper Van Bourgognie
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  • Wrote 256 posts
  • Member since 21 Feb 14

Should be fixed, let me know if it is or ain't

Christian Ehlers
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  • Wrote 49 posts
  • Member since 18 Sep 14

Should be fixed, let me know if it is or ain't

The images now seem to be resized to fit the screen resolution of the browser so the text is readable without problems.

If you want to make it even better, allow clicking on images to show them in full size using one of those fancy picture overlays... :)

Jan Hünnemeyer
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  • Wrote 5 posts
  • Member since 7 Nov 14

Great HOWTO, thanks Thoralt! It really helped me as an beginner. Can we please somehow pin this on top of everything / make it more visible?

Jasper Van Bourgognie
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  • Wrote 256 posts
  • Member since 21 Feb 14

Pinned it - Better might be to move it to the wiki. It's linked now from the top menu (community > wiki).

You are required to make (another, sorry for that) account there if you want to edit pages.

Alvaro Gutierrez
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  • Wrote 1 posts
  • Member since 1 Dec 14

Hi, I have just received the Smartscope!

When we connect it to the AWG pin, should we connect also the ground aligator to the ground pin?

Another question, how can I adjust the values? It is very hard to put it in 100mV (at least in a Mac).

Cheers.

Riemer
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  • Wrote 457 posts
  • Member since 20 Feb 14

Normally you should always connect the ground clip, but in this case it's not needed as the grounds of AWG and scope are already connected -- they're the same device.
The sliders are quite smart -- if you want fine control, move your mouse/touch pointer up or down away from the slider. The farther you go, the finer the control. Need to work on the wiki..

Jens
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  • Wrote 6 posts
  • Member since 6 Dec 14

Okay. I guess I have no clue what I am really doing here, but trying to do this calibration thingy I end up with this: calibation screen

All I get is some noise but no square waveform. I does not matter what "Function" I select and upload - output is always the same. Probes are set to 10x.
Any hints?

PS: I am using v0.0.7.0 on OSX - this release has some major improvements over 0.0.6.0 and seems much more stable.

andrei
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  • Wrote 18 posts
  • Member since 5 Mar 14

Jens, did you perhaps forgot to physically connect the probe(s) to the AWG pin (third from left to right, bottom row)?

Jens
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  • Wrote 6 posts
  • Member since 6 Dec 14

perhaps forgot

"forgot"... :) kind of.
This information somehow demystifies this whole calibration process for me. Stupid me.

Works perfectly now.

drs
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  • Wrote 9 posts
  • Member since 1 Apr 18

Edit:
Sh..., took me 3 more hours to recognise that the cable to AWG had contact problems :-(
So...forget my question..

Hallo, I'm new to Smartcope ... bought some days ago with good offer for my Arduino projects.
I tried to follow the calibration guide but my square wave seems to look totally different than pictures in this tread.

https://imgur.com/gczZ2Ur

What I'm doing wrong?

Thanks
DRS

Ian Turner
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  • Wrote 6 posts
  • Member since 10 Aug 16

Edit:
Sh..., took me 3 more hours to recognise that the cable to AWG had contact problems :-(

What I'm doing wrong?

Thanks
DRS

I am in the same boat, I cannot even FIND a menu that shows the AWG option I amsupposed to use ?

Please provide some more detailed info on this critical area.

Joe Horn
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  • Wrote 72 posts
  • Member since 19 Apr 17

The pictures above show a quite old sofware version. The menu structure today is a bit different. You find it currently under "Generator-Analog". And the functionality has been increased. Maby this can help you:
http://wiki.lab-nation.com/index.php/Arbitrary_Waveform_Generator_(AWG)

Ian Turner
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  • Wrote 6 posts
  • Member since 10 Aug 16

Hi Joe,
Thanbks for that, it looks far more useful info, but I have encountered a rather show stopping problem...

Mot Every time, but quite often, I power up my Smartscope, using the 2nd from let USB input, my mouse cursor disappears entirely from my screen. Worse than that, if I unplug the scope, my mouse still does not come back, and my only recoveryu methodI have found so far is to use a USB based radio mouse. I have to plug that in, turnb it on via it's button, move it around a bit, and then remove it's USB ID plug again, and most times my original mouse cursor returns.

Makes it pretty hard to reach the AWG stage really - Any Ideas ? W10 Homne system, USB MOUSE, lotsof other USB thingies hung on to it.

Howeber, I have managewd to reach the situation of AWG connected to one probe, GND pin on right connected to other probe, 5v power to same input, and ANALOGUE selected in the menu. The Smartscope menu does not say Generator, it say DUMMYSCOPE !!!!!!. So does the Aboput box ?????

Matt
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  • Wrote 625 posts
  • Member since 4 Dec 14

Keep in mind that normally the probes come pre-calibrated from the factory, which means no action is strictly required.

that said, the issue regarding the disappearing mouse is new and probably related to your setup. Seems like a conflict on your USB but -- even though not sure how this might be possible. only way to find out would be to unplug all USB devices and test out one by one which one creates the conflict.

Dummyscope is there when no smartscope is detected on the USB bus. Only in case you have a smartscope connected, you will see the AWG entries in the menu.