The Mystery of the Weird Scope Readings

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So, this is a strange one! ‪@TheSmokinApe‬ and I have been puzzling over some weird things happening with our oscilloscopes. Ape found the problem in his, and I verified seeing the same thing in mine. What's even stranger - some of the results we got on different 'scopes!
Amazon Affiliate Links for equipment in this video:
UNI-T UTG962 AWG - amzn.to/3KzNiol
Siglent 2202X-E Oscilloscope - amzn.to/3xbwTmZ
Rigol 5074 Oscilloscope - amzn.to/3Xl1NEl
Owon HDS2102S Oscilloscope - amzn.to/3VhP2Yd
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Опубликовано:

21 сен 2024

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Комментарии : 24

@TheSmokinApe 3 месяца назад

Strange things are afoot at the Circle K!

@hkmp5s 3 месяца назад

But they got nice usb cables.

@haxwithaxe 3 месяца назад

Ape is clearly the mad hatter. I don't know what character Jim is.

@WECB640 3 месяца назад

Jim is one of the men on the chessboard, always telling me where to go. LOL

@FEPLabsRadio 3 месяца назад

I sang that comment in my head Hollywood!

@jamespurser357 3 месяца назад

Swap channels 1,2 and see if the readings change to verify the issue is in the set up not the scopes. Then make changes one change at a time to identify what changes the reedout

@FEPLabsRadio 3 месяца назад

I did that in the video - the strange readings are only on channel 1. moving any cable to 2-4 read what is expected.

@LeeMcc_KI5YPR 3 месяца назад

First, I was expecting a Rick roll. 😉 Ch 1 and 2 showed the amplitudes looking the same, but the vertical scales were different so they should have looked different. This was on both scopes. Set them the same. Next, use DC coupling, even if the arb has zero DC offset. If that does nothing, add some DC offset to the arb, maybe 1/2×Vpp. Hypothesis being something is odd about the ac coupling. Also try a higher frequency. I cannot imagine them sucking this bad, but AC coupling is just a high pass filter. 1kHz might be on the edge and one channel might be off. If that changes results, try a lower freq (maybe 100 Hz). If I think of something else, I'll be back.

@FEPLabsRadio 3 месяца назад

Dammit, that would have been funny! I played with both, same results, and only on channel 1 on 2/3 of scopes. I originally was using 10Mhz (that's what Ape had started with), and got the same results. I just backed down to 1, so i engage the bandwidth limiter on the rigol. It's weird for sure. Yeah, I know the amplitudes looked the same, since the VPP read lower, I just adjusted the vertical til they were both on the screen. That shouldn't affect the readings on the measurement though? Ape and I were thinking about doing a live stream in the next week, to ponder this some more. I'm not the worlds best scope monkey, but this seems like basic stuff. Lee, the other strange thing is that the onboard arb in the rigol gave me the same flaky results as the external one. For the video, I just used the external one. Also, the strange results stayed on channel 1, and only channel 1. Literall unplug the cable from 1 and move it to 3 or 4, and they read the correct VPP. "Never gonna give you up, never gonna let you down..."

@LeeMcc_KI5YPR 3 месяца назад

@@FEPLabsRadio Right, vertical should not change the measurement.

@WECB640 3 месяца назад

I see a potential clue.... On both the Rigol and the Siglent, the correct Vp-p is shown on only one channel, and that channel is always FIRST in the bottom of the screen. One would think that they would be in order ie. CH-1 is always first followed by CH-2, CH-3 etc. I believe you have a setting that is selecting only one channel to be the MAIN one (perhaps this is is selected by the trigger setting) and the other channel (with the incorrect Vp-p reading) is displaying the OFFSET difference between them on the display screen. I see that they are not positioned at equally opposite sides of the zero equator on the screen. Take a look at the RIGOL manual, (Chapter 4) "Acquisition Mode". CH-1 may be set differently than CH-2 or CH-3. PS. The Owon isn't sophisticated enough to have this setting error, and that's probably why it displays the correct values. I suspect the software is working correctly, but this is an operator error because "men don't read directions". PS. That applies to me also. LOL 73

@FEPLabsRadio 3 месяца назад

That's my first thought, i'll go back to the manual. At first it acts like an impedance mismatch, but that isn't the case. I realized they aren't positioned equally, but it seems that the measurements would be based on the actual signal, not the screen position? Also, I have them scaled to both fit on the screen, so the volts/block is not the same. It's curious for sure.

@WECB640 3 месяца назад

@@FEPLabsRadio Chapter #4 "Acquisition Mode" determines how the scope reads the sample bits of the waveform. Also, CH-2 is displayed first on both scopes when measuring Vp-p. One is master, the other servant. I think you'll find it in the settings after you have a few Dr. Peppers. "GOOD LUCK JIM. This message will self destruct in 5 seconds."

@DeVibe. 3 месяца назад

@@WECB640 it's still there.

@Bill-HRT 3 месяца назад

Jeem! When Ape and you go down the service equipment rabbit hole I rarely interfere because I don't want to cause any ill will. But this one is simple, buddy. Your high impedance franistan is coaptualating with your input arugalator. Simple fix . . .Turn it off, and go play radio, lol Great video. Thanks for making me a wee bit smarter. See you out there. 73 de Bill

@FEPLabsRadio 3 месяца назад

Dangit, I hate it when that happens!

@PaulGriffith 3 месяца назад

Might be a design flaw where a lazy developer used the reference schematic on a chips data sheet and didn't realy invest time to design a proper circuit. That has happened. A similar thing can happen when a programmer reuses a chunk of code from a common library or another product.

@FEPLabsRadio 3 месяца назад

That's what it feels like Paul. Amazingly Siglent and Rigol suffer from the same library/code/chip issue, but only on channel 1.

@DeVibe. 3 месяца назад

Maybe some nasty ESD events caused damage to the input stage of the most used channel of your scopes.

@nianfengli6121 3 месяца назад

Strange. But we need more test data point ... how about testing at 50Ohm impedance, how about higher/lower amplitude, how about much higher frequency or other waveform ... the issue can be anywhere, for example, both scope channel 1 been damaged in previous use.

@FEPLabsRadio 3 месяца назад

I don't have any way to come up with a different impedance - either 50ohm, or high-z. The behavior follows the same pattern at 10Mhz (originally where we found the issue). As for 2/3 scope channel 1's being damaged, I consider that unlikely. Both of these were purchased new, and have light use at my house, and that's it. I think it's a common library/firmware thing that rigol and siglent have. The odd results only stay on channel 1. The owon handheld worked fine. Also - @thesmokinape had the weird results on his rigol scope as well.

@nianfengli6121 3 месяца назад

@@FEPLabsRadio Thanks for the update. Other testing can be connect channel 1 to other signal source (like just test a 1.5v battery DC voltage) compare to channel 2, to make sure it is not damaged. And/or a factory reset on the oscilloscope.