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Author Topic: Test Equipment: Oscillocopes  (Read 58008 times)

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #180 on: February 27, 2015, 06:08:12 AM »
Brian,

I thought I would add this regarding the trigger holdoff.

As in my previous post, when the trace reaches the far right side it returns to the left side very quickly and sits off screen waiting for the next trigger pulse.  Once the trace gets back over to the left side, the trace has to rearm itself to prepare for the next trigger pulse.  The trace normally rearms itself very quickly so it responds almost immediately to the first incoming trigger pulse that arrives after the trace returns to the left.

Adding trigger holdoff using the trigger holdoff control causes the trace to just sit there on the left side off screen ignoring any incoming trigger pulses for the amount of time the holdoff control is set for.  Once the holdoff time expires, the trace again rearms and begins scanning to the right on the first trigger pulse received after the holdoff period.

This can be useful when looking at a series of brief pulses separated by a fair amount of time (such as data bursts).

For now, set the holdoff to normal and leave it there until you become more familiar with your scope.  You will not be needing to use any trigger holdoff for a while.

PW   

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Re: Test Equipment: Oscillocopes
« Reply #180 on: February 27, 2015, 06:08:12 AM »

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #181 on: February 27, 2015, 06:48:13 AM »
Good stuff guys, it's all comin together nicely now. I'm finally starting to understand this nifty tool.

I noticed that the 'Scope' Visualization in VLC media player is pretty accurate. I'm able to get the settings right on the Tek to pretty much match the traces that it shows.
Too bad it doesn't have XY mode, though. Is there something that I am missing where I'm able to get a more focused X-Y trace? I notice that it's a little bit better when I unplug my headphones, so maybe it's just the quality of sound from the PC output?

It's not the quality of the music files... I downloaded the .flac files. Turned off all enhancements everywhere.

Seems I figured it out... X1 probe, Max volume from the PC, 50 or 100mv/div, high intensity, unplug headphones ( :(  )   I'm sure there's a way to add a little power into the signal to compensate for the HP loss, but that's for some time later on. Unless it's uber easy..

Brian

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #182 on: February 27, 2015, 07:55:08 AM »


I'd still like to see what the X-Y trace looks like. With no inputs (both channel input coupling switches to Ground) the X-Y display should give a single non-moving dot, that you can position to exact center screen with the vert and horz position controls and focus to a tiny dot. Don't leave it there too long or too bright, it will burn the phosphor. Then if you give both channels the same input from the calibrator you should see a diagonal line. (Both channel V/div at same settings)

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Re: Test Equipment: Oscillocopes
« Reply #182 on: February 27, 2015, 07:55:08 AM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #183 on: February 27, 2015, 08:08:25 PM »
TK -

Here's a video of me going through the X-Y display test that you suggested.  I am able to get the centered dot with the inputs at Ground, but I do not get the single diagonal that it sounds like I should be getting. Let me know if you need any more info than what I gave about my settings.  Hopefully it's just a human error issue, or at most a calibration issue.

In the video I had the probes on X1.  I tried it before the vid with X10 and the only difference it made was where I had to have my V/div set, and gave the exact same traces.

https://www.youtube.com/watch?v=jnsx32d2krY

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #184 on: February 27, 2015, 09:24:53 PM »
Hmm. That looks "almost" normal, but there should be only a single diagonal line between the endpoint dots. Let's make sure you have the scope set properly.

The Time/Div switches should be locked together and on X-Y mode, the "Var" knob in the cal detent. Horizontal Display in "A" . For looking at the calibrator signal, the V/div controls should both be set to the same value and the "var" knob in its cal detent. No Bandwidth Limit. Yes, the Vert Mode should be in CH2 for the x-y display. CH2 "invert" out, not inverted. AC-coupled inputs should help center the X-Y display, that at least looks like it is working right. The x-y display is not triggered so the trigger controls shouldn't make any difference. Be careful about the Intensity control. If the display is working correctly you should be able to get decent brightness of the diagonal line without blasting out the endpoint dots.

Don't connect your probe Grounds to the Calibrator output! This short-circuits the Calibrator! The probe grounds are already connected to the Chassis ground internally by the BNC connectors and you should not have to connect them to anything when using the Calibrator... especially not the Calibrator output!
Please use 10x probe attenuation whenever possible, and set the V/div knobs appropriately!

The display "should" be a single diagonal line between the two endpoints. The scaling and angle of the line depends on the V/div settings of the channels. If both V/div knobs are set the same the line should be 45 degrees, sloping up from left to right, and the length scaled by the V/div settings.

If the display is different from that, like with the two lines, and the scope is set properly, there may be an issue with calibration, or the probes themselves even. Please repeat the test with the probes set to 10x and let's see if you can get a nice single diagonal line, bearing in mind what I said above. You may want to check and adjust the probe compensation adjustments again, using 10x attenuation, the normal time-domain display and the nice square wave from the calibrator according to the instructions for doing that.

(When the x-y display deviates from the single diagonal line this normally means that the two signals are out-of-phase. With both V/div knobs set the same, a perfect circle means 90 degrees out-of-phase and a diagonal line sloping _down_ from L to R indicates 180 degrees out-of-phase. See the image attached below. Since both signals are coming from the same Calibrator source they should be perfectly in phase. So there is some issue here, again presuming that the controls and probes are set properly.)

I noticed that it looks like both V/div readout lights are on in the upper V/div switch. This is a fault. When there is no probe with a readout pin connected, only the "1x" light should be on, and you need to remember to read the knob scale at the unlit 10x position when you are using 10x attenuation on your probe.
OH>>> never mind, I took another look and it seems that that is just a glare from the room light reflecting on the switch. Never mind....  :-[

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Re: Test Equipment: Oscillocopes
« Reply #184 on: February 27, 2015, 09:24:53 PM »
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Offline MileHigh

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Re: Test Equipment: Oscillocopes
« Reply #185 on: February 27, 2015, 10:22:25 PM »
Note Brian's source is not an audio signal, it's the calibrator square wave.  So two diagonal dots on the screen with very faint lines in between is correct.  It looks like in the beginning of the clip the two input gains are too high so you don't see the two dots.  Towards the end of the clip he turns down the input gains and all is good.   The scope looks fine.

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #186 on: February 27, 2015, 10:29:37 PM »
TK -

Here's a video of me going through the X-Y display test that you suggested.  I am able to get the centered dot with the inputs at Ground, but I do not get the single diagonal that it sounds like I should be getting. Let me know if you need any more info than what I gave about my settings.  Hopefully it's just a human error issue, or at most a calibration issue.

In the video I had the probes on X1.  I tried it before the vid with X10 and the only difference it made was where I had to have my V/div set, and gave the exact same traces.

https://www.youtube.com/watch?v=jnsx32d2krY
It looks right to me.

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Re: Test Equipment: Oscillocopes
« Reply #186 on: February 27, 2015, 10:29:37 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #187 on: February 27, 2015, 11:18:22 PM »
Note Brian's source is not an audio signal, it's the calibrator square wave.  So two diagonal dots on the screen with very faint lines in between is correct. (snip)

Well, maybe. My Tek 2213a gives a better balance between the bright dots and the line, though, when using the Calibrator input.  The line shows up better than in Brian's video when the dots are reasonably bright. Maybe this is a result of the camera not showing the lines well in Brian's video.  I still think the two parallel lines are weird, though. There should only be one line, with length depending on V/div settings and angle at 45 degrees if both V/div knobs and probes are set the same.

Inverting the CH2 input should make the line slope in the other direction, sloping down from L to R. With two square wave inputs of adjustable phase it is possible to have a square of 4 dots with very dim or invisible lines between them, or an "L" shaped line with two bright end dots and one dimmer corner dot, depending on the phase of the square wave signals. But two parallel diagonal lines.... I don't think that should be happening.

I've shot a little video showing the use of the x-y mode to display phase shifts, but I used a pair of sine wave signals instead of square waves. This does make a difference in the brightness of the displayed diagonal trace. I'll post the link to the video when it's done uploading.

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #188 on: February 28, 2015, 12:21:04 AM »
TK -

I had everything set the way you described it, except of course for the probe atten setting.  I will try again with 10X, even though I tried that before I made the vid and got the same results, just had the shift in the V/div settings to compensate.

I will also try the same thing using the FG from my PC and a pair of in phase sine waves. If I don't get the proper diagonal line, I will adjust phase until I do, and post the results.

I will also try everything with the original Tek probes. First test with the cheaps then the Tek's, then second test with cheaps then Teks.

From what everyone is saying, it seems like the results of doing so from the scope calibrator varies in some brands/models.

The video I shot is showing the correct brightness that corresponds with what I see on the scope screen. I don't have it set to compensate for lighting conditions so that you see exactly what I see.  I've been trying to adjust my lighting in here to give the best view without glare on the video, but I haven't managed to hit it right just yet.  I'm working on setting up a mini-lab with some shelves and a big desk so I can give my equipment a more permanent home, and then hopefully I will be able to set up a more permanent lighting system for better vids. Maybe if I try LED lighting, or christmas lights..... haha

Brian

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Re: Test Equipment: Oscillocopes
« Reply #188 on: February 28, 2015, 12:21:04 AM »
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Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #189 on: February 28, 2015, 12:39:58 AM »
On my TDS2024:

A 1kHz square wave using equal length cables to the channel inputs generates two dots.  If I turn on infinite persistence then eventually two more or less diagonal lines form.

A 10MHz square wave also using equal length cables makes kind of a hysteresis "S" shape.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #190 on: February 28, 2015, 01:20:04 AM »
Hmmm.... The "two lines" figure from MarkE looks to me like a little bit of phase difference in the two signals. At least that is what two signals with a slight bit of phase difference _should_ look like. But I agree, in a perfect world two perfectly in-phase and perfectly symmetrical square waves should produce two dots with a dim line connecting them or no line at all. A pair of in-phase sine wave signals will produce a more definite diagonal line. I think that the two lines that build up in MarkE's infinite persistence figure may indicate a slight bit of phase jitter or noise, possibly in the scope itself since the signals are coming from the same source, or an imperfection in the square wave signal.

My video demonstration using sine wave signals is here:

http://www.youtube.com/watch?v=mV1IHnIHaC8


Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #190 on: February 28, 2015, 01:20:04 AM »
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Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #191 on: February 28, 2015, 01:58:31 AM »
It is a slight asymmetry in the frequency response of the amplifiers.  The driving signal has a rise time that is faster than either amplifier can track.    If I drive with a signal that doesn't have such fast rise times, then I get the expected diagonal line seen below.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #192 on: February 28, 2015, 01:58:53 AM »
Heh.... here are a couple of soundfiles to look at using X-Y mode....

http://frozenhaxor.pl/pliki/youscope.wav
http://frozenhaxor.pl/pliki/oscillofun.flac

Found these on a video demo here:
https://www.youtube.com/watch?v=3U7I3if3TtM

They display quite well on my Tek 2213a!

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #193 on: February 28, 2015, 04:13:38 AM »
So everything is looking pretty good so far. I'm not getting the diagonal line off the calibrator, but when I set it up off the calibrator with both traces overlapping, about 3 cycles on screen, and then switch to XY, I get two dots at very close to 45 degrees in the proper direction. When I invert Channel 2, it inverts the diagonal properly. See the pictures below.
I ran the same test using the two original Tek probes I have (the 6062A I rebuilt, and the 6065A that the scope came with) and the 6065A is acting up a little. I'd like to be able to use it with the 6062A when I need a pair of high quality probes, so if it's something fixable I'd like to try and fix it. I made a vid of the calibrator sq wave to X-Y with those probes and showed what the issue is with the probe.  If it's too much of a pain to remedy I'll just set it aside for some other time.

I'm about to run both pairs of probes using the sine wave to make sure I get the actual line, play with the phase settings, and then check out the links that TK posted and have a little fun with it.
I got a little carried away getting my mini-lab set up or I'd have already done all this testing. But hey, at least I'm about ready to populate it, run a 110V dedicated line to it (all that I have there for now is an old ungrounded outlet!!) and set up some lighting..

http://i1081.photobucket.com/albums/j347/Brian_Bloom/CAM00224x_zpsmipym7fq.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/CAM00222x_zpsfa467i5m.jpg
http://i1081.photobucket.com/albums/j347/Brian_Bloom/CAM00223x_zpsvwlcd5pg.jpg

Vid should be done uploading shortly:
https://www.youtube.com/watch?v=msbXPU_l_aw


Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #194 on: February 28, 2015, 04:21:46 AM »
How are you able to upload a pic to the OU server as an attachment and it show up as a link instead of the picture?   I guess my method works fine, but I'd still like to know. Is it just the type of file you are attaching? Is it that if it's not a jpg  or gif file, it displays as a link?
I mean, I like not having to click on a link and all that to see a picture, but in these forums it's better to have links instead of the pic, especially if there are multiple. Saves from having to load page after page just to go a few posts back or forward.

Brian

 

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