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Author Topic: Test Equipment: Oscillocopes  (Read 57366 times)

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #210 on: February 28, 2015, 08:02:00 PM »
There is a simple test:  Hook your laptop to an AC powered stereo.  If you get a bunch of 60 cycle hum then you have a bad ground connection.  If not, then there is something else going on with your oscilloscope set-up.

When I have the laptop hooked up to the AC powered stereo unit (with the unit on only stereo mode, no enhancements such as surround, dolby, etc) It works perfectly.  no hum at all.  It plays music without any hum at any volume, without any input from the laptop with the stereo volume up, and with a 1khz sine wave output.

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Re: Test Equipment: Oscillocopes
« Reply #210 on: February 28, 2015, 08:02:00 PM »

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #211 on: February 28, 2015, 08:08:18 PM »
It works perfectly when plugged into an AC powered stereo.  no hum at all.

Brian,

When you say "it" works perfectly, do you mean that when the laptop HP jack is connected to the input of a stereo audio amplifier, you can produce, for example, a 1KHz sine wave output from your FG software and HEAR a nice steady 1K tone from both the left and right channel of your stereo's speakers (or headphones)?

PW

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #212 on: February 28, 2015, 08:23:25 PM »
Brian,

When you say "it" works perfectly, do you mean that when the laptop HP jack is connected to a stereo audio amplifier, you can produce, for example, a 1KHz sine wave output from your FG software and HEAR a nice steady 1K tone from both the left and right channel of your stereo's speakers (or headphones)?

PW

1khz sine wave played from PC FG into AC sound system set on stereo-
https://www.youtube.com/watch?v=zfmSXja5Iz0

I also noticed that when I have it on X-Y with no input and on 5mv/div, it's not just a dot in the center.  If I turn the intensity up a little, I can see what looks like half of the infinite symbol emerging from the dot towards the top of the screen, so more or less a teardrop shape with the point being at the dot.

(where's the 'smashing my head into the wall' emoticon thing??  :(    )
Brian

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Re: Test Equipment: Oscillocopes
« Reply #212 on: February 28, 2015, 08:23:25 PM »
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Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #213 on: February 28, 2015, 08:49:27 PM »
1khz sine wave played from PC FG into AC sound system set on stereo-
https://www.youtube.com/watch?v=zfmSXja5Iz0

Brian

Brian,

OK, the FG software appears to be working fine. 

From your previous video:

Regarding your "dot" on the far left.  It's probably just the "beam off" blanking level for your trace while waiting for a trigger.  What does it matter if you have to crank the H position way over and crank up the brightness to see it?

I don't see evidence of what I would consider an open ground in the video you posted.

Personally, I think you should for now just focus on getting decent displays using just one channel.  Use only channel one for a while, set the H position so that the trace is centered left right and leave that knob alone for now.  Same with the trigger holdoff.  Set it to norm and leave it there.

Select to display only channel one with trigger source set to channel one.  Once you get good at displaying various waveforms with channel one, then you can move on to dual channel use.  Before doing so, practice getting decent channel one displays so that they are centered in the upper half of the display (using vertical position) with the vertical sensitivity set so that the displayed waveforms do not use any more than the upper half of the display.  This clears the lower half of your display for use with channel two.

I am not sure what your calibrator's frequency is, they are typically 1KHz, but I believe its amplitude is 300mv pk to pk.  Using just one probe and channel one, get good at displaying the calibrator signal.  I would select AC coupling on the channel input and AC coupling on the trigger source (just in case any source has DC offset).

Once you are confident with using channel one to produce stable views of 3 or 4 cycles of the calibrator waveform, set your PC based FG so that it produces a square wave of the same frequency (1K?) and of similar amplitude as your calibrator.  Connect your scope probe's ground lead to the HP jack's sleeve (gnd) connection.  You should then be able to move your probe tip connection between the calibrator and one channel of the laptop's HP output, and without flipping any scope switches, see the same waveform displayed in a stable fashion.  Adjust the PC based frequency and amplitude as necessary so that when it is displayed, it closely matches the calibrator display.  The point of this is, that if you can get a stable display of the calibrator signal, and if the calibrator and PC based FG are producing the same signal, you should be able to see either one without changing any scope settings.

Now, once you can do that without issues, and if you have the calibrator or FG display confined to the upper half of the scope's display, select ALT for a two channel display.  Set the CH2 vertical sensitivity the same as CH1's sensitivity (and with AC input coupling).  Connect a probe similar to CH1's probe (X1 or X10) to the CH2 input and connect its tip to the same point you have the CH1 probe tip connected.  Adjust the CH2 vertical position control so that the CH2 waveform is centered in the lower half of the display.  You should now have two identical looking waveforms displayed, CH1 in the upper half, CH2 in the lower half, and the displayed waveforms should not be overlapping vertically.  You should also be able to move the probe tips between the calibrator and the PC based FG output with the displays remaining stable and looking similarly.

Once you get this far, you can connect CH2's probe to the second channel of the PC based FG output for display of independent FG channels.

Regarding your last video:

Does your stereo audio amp have a preamp out or record output?

You might consider using a pair of phono cords to bring the line/record out from the stereo over to the scope and connect your scope to the phono plugs at the end of the phono cords.  In the absence of phono to BNC adapters, you can use alligator clip leads to go from the tip of the phono plugs to the scope probe spring hooks.  Trying to hook the phono plug tips directly might be a bit rough on your probe hooks (alternately, cut and strip the ends of a spare phono cord).  You only need to hook up one probe ground lead to one phono plug's ground (or use another clip lead between your scope's ground jack and one of the phono plug shells.

But, as above, consider using only one channel for a while until you are good at getting a stable display on just channel one.

PW

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #214 on: February 28, 2015, 08:54:20 PM »
Made a vid to show the results of this test. From what I gather from your explanation, for some reason I do not have a ground/common connection from the laptop to scope.  Let me know your thoughts on the matter.   Also, I pointed out that there is a little dot to the left, just off screen when centered, when the scope is in standby mode. Is that normal? Watch vid and then you will understand the pic that I linked to.

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

http://i1081.photobucket.com/albums/j347/Brian_Bloom/CAM00254_zpsxtm5ctp2.jpg

The dot is normal and usually off the screen to the left when you are displaying a signal.

To check for the improper ground 60Hz hum, you should change the Trigger Source to "LINE" and see if the trace stabilizes. I kept wanting you to do this in the video but you didn't.   :'( You used every other control but the one that would show the 60 Hz noise if it was there. Also at 6:25 or so when the screen blanks... you are in NORM trigger mode and the trigger _level_ is set outside the range of the signal, so the screen blanks! Slow down please... think about what you are doing. If the screen blanks but you know you have a valid signal input, the FIRST thing to check is the Trigger Level setting. Ah...I'm writing this as I'm watching and at 6:35 or so you finally adjust the Trigger Level and get a trace. Good! But you never tried "LINE" on the Trigger Source.... If there is a 60 Hz hum coming from the lack of proper grounding this will show up as an "envelope" for your actual main signal, making it wobble up and down or other weirdnesses. If you select "LINE" on Trigger Source the scope will trigger on the mains input to the power supply and any weirdness caused by the 60Hz hum will stabilize. The main signal will "run free" of course but with the proper timebase setting for 60 Hz you can view the stable "envelope" or other 60Hz weirdness on the main signal when "LINE" is selected as the trigger source.

A 60 Hz waveform has a period of (1 sec/60Hz) = 0.0166 seconds or 16.7 milliseconds. 3 full cycles would then take 50 milliseconds. Your screen is 10 divisions wide, so to display 50 milliseconds worth of signal across the screen you set your timebase to 5 ms/div. Then set Trigger Source to LINE. If you then see a stable "envelope" of three cycles with your main waveform running inside that envelope, you have identified your problem to be a 60 Hz hum most likely coming from a bad signal ground.

You could also do this: With the connections between scope and headphone jack on the PC made as you have tried them, and both the Scope and the PC turned OFF and unplugged from the wall, use a DMM to check the ground connection for continuity and resistance. Touch one DMM probe to the BNC shields at the scope and the other DMM probe to some ground on the PC, like the USB shield or the headphone jack outer part, to see if there is high resistance or open circuit in your ground connection from the scope to the PC.

Don't get so frustrated! You are learning a whole lot about scope operation and etc. that you would never have learned otherwise, and you have the satisfaction of bringing this classic and sensitive instrument back to life! That is nothing to sneeze at. The Oscilloscope is the King of test equipment and is a complex bit of apparatus, as you can see, and your scope isn't exactly a "beginner's" scope, it is considerably more complex than many lesser instruments, with its delayed timebase features etc. You are on a very steep learning curve and you are doing just fine, so don't be so hard on yourself.

ETA: Take PW's advice to heart. I can add this: SLOW DOWN. Every time you change a setting, stop for a few seconds, observe, and _think_ about what you see or don't see. The scope is a very complex instrument, but it is dumb, and it only does what you tell it to do. If you tell it nonsense, you will get nonsense back from it. GIGO applies in full force here.
And lighten up, you are getting such a valuable education here, and I'm quite sure that others are watching along and also benefitting from our explorations here.

And here's your head-banging smiley: 



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Re: Test Equipment: Oscillocopes
« Reply #214 on: February 28, 2015, 08:54:20 PM »
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Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #215 on: February 28, 2015, 09:18:06 PM »
When I have the laptop hooked up to the AC powered stereo unit (with the unit on only stereo mode, no enhancements such as surround, dolby, etc) It works perfectly.  no hum at all.  It plays music without any hum at any volume, without any input from the laptop with the stereo volume up, and with a 1khz sine wave output.
Well when a circuit cannot support DC (the exponential decay in your square waves) and the common is connected, then somewhere a blocking capacitor has been inserted, such as by setting the oscilloscope input to AC.

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #216 on: February 28, 2015, 09:30:39 PM »
Well when a circuit cannot support DC (the exponential decay in your square waves) and the common is connected, then somewhere a blocking capacitor has been inserted, such as by setting the oscilloscope input to AC.

MarkE,

I think we should all just focus on getting Brian to the point where he can get stable, correctly triggered displays on his scope.

A bit of tilt is the least of his problems at this point.

In the last video of his scope in action, I wanted to turn off CH2, speed up the horizontal and adjust trigger level for a stable display.  Looks like he had one of the channels vert. sensitivity cranked up much higher than the other (or different probe factor), horizontal sweep way to slow, and that it was not triggering.  It has been some time since Brian has produced a video of a stable display, tilt or no tilt.

PW

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Re: Test Equipment: Oscillocopes
« Reply #216 on: February 28, 2015, 09:30:39 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #217 on: February 28, 2015, 09:37:13 PM »
(snip)
I also noticed that when I have it on X-Y with no input and on 5mv/div, it's not just a dot in the center.  If I turn the intensity up a little, I can see what looks like half of the infinite symbol emerging from the dot towards the top of the screen, so more or less a teardrop shape with the point being at the dot.

(where's the 'smashing my head into the wall' emoticon thing??  :(    )
Brian

Do you get that when both channel input coupling switches are set to "ground"? And the scope is fully warmed up, and the "focus" knob is adjusted for the best focus?

If the above are true, then you could try adjusting the "Astig" astigmatism control slightly to see if it improves the shape of the dot, but try to remember where it was set before so you can put it back if you get no improvement.

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #218 on: February 28, 2015, 09:52:58 PM »
Do you get that when both channel input coupling switches are set to "ground"? And the scope is fully warmed up, and the "focus" knob is adjusted for the best focus?

If the above are true, then you could try adjusting the "Astig" astigmatism control slightly to see if it improves the shape of the dot, but try to remember where it was set before so you can put it back if you get no improvement.

TK,

Hopefully his "infinity symbol" goes away when he sets the input switches to ground.  Regardless, I think he should stop tweaking his scope 'till he is a bit more comfortable using it, and actually knows what is and isn't working.

I thought he was able to produce a stable, dual channel display of the calibrator some time ago.  He should get back to that point before moving on.

PW 

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Re: Test Equipment: Oscillocopes
« Reply #218 on: February 28, 2015, 09:52:58 PM »
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Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #219 on: February 28, 2015, 10:14:27 PM »
Sure, I can agree with that... but I also encourage experimentation when done in an orderly manner, with time to analyze the results of each change in a variable!


Meanwhile... on the issue of improper signal grounds and use of the "LINE" trigger source:

I've just shot another video demonstrating the use of the "LINE" trigger source to find and display line noise (60Hz hum) superimposed on a signal of interest, caused by improper or insufficient signal ground at the scope.  This video will be ready to view in a few minutes.



Meanwhile, slightly off topic, here's my "scoposcopy" video on the basics of determining frequency of a signal using an analog scope, featuring the classic antique Tek RM503 precision low-frequency oscilloscope:

Frequency in Hz = 1/(period in seconds)
and of course
Period in seconds = 1/(frequency in Hz)

http://www.youtube.com/watch?v=teXXF0a_WoI

(Apologies for the poor video quality, this was before I found the right transcoder to use with my camera... )


ETA: The Line Trigger/Mains Hum video is ready here:

http://www.youtube.com/watch?v=spGpBz4K8rU

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #220 on: February 28, 2015, 11:25:42 PM »
MarkE,

I think we should all just focus on getting Brian to the point where he can get stable, correctly triggered displays on his scope.

A bit of tilt is the least of his problems at this point.

In the last video of his scope in action, I wanted to turn off CH2, speed up the horizontal and adjust trigger level for a stable display.  Looks like he had one of the channels vert. sensitivity cranked up much higher than the other (or different probe factor), horizontal sweep way to slow, and that it was not triggering.  It has been some time since Brian has produced a video of a stable display, tilt or no tilt.

PW
His square waves were collapsing.  High pass had a shorter time constant than one half of each cycle.   Like you I thought that he had operation with the calibrator working.  I think he just needs to learn some basic skills:  read the manual and try things out with what he has on hand.

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Re: Test Equipment: Oscillocopes
« Reply #220 on: February 28, 2015, 11:25:42 PM »
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Offline Pirate88179

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Re: Test Equipment: Oscillocopes
« Reply #221 on: February 28, 2015, 11:39:34 PM »
What about that one trimpot he adjusted a little while back?  I would have thought that you needed another scope to tune those if calibration was off.

I believe he said he did not turn it much but, could that small adjustment cause any of this?  Maybe he could turn it back to about where it was?

Just wondering...most, if not all, of this is over my head.

I was blown away by TK's video of the weird shapes playing on his scope with the sound input.  How he inverted and made a mirror image of that logo is beyond me.  Unless, that is the way it is suppose to be?

Bill

ETA: https://www.youtube.com/watch?v=OxlCoKN4W7c

EEVblog made a similar video, and his logo is reversed also!  Probably supposed to be that way then....

PS  Dave said that Youscope was developed by a 15 year old kid a long time ago.  Holy crap!

Dave also runs it on his digital scope and..he really has to play with it to get rid of the fly back lines.  It does not look nearly as cool as it does on an analogue scope.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #222 on: March 01, 2015, 12:12:29 AM »
It's interesting that Dave's Hameg analog scope shows the text backwards, like my 2213a does, but the Agilent shows it the right way around. I wonder why that is. I can't get mine to display the text frontwards by inverting the CH2 (y) channel, or by swapping L and R (this makes the text run up and down instead of across). So maybe he has a way to invert the CH1 (x) channel on the Agilent and this is the cause. It's a mystery to me for sure.

I'm also wondering if that's the best display that the Rigol could do. It's supposed to be able to do some huge number of waveform samples per second, I thought, so I expected the display to be better than that. Maybe he has the sample rate at some non-optimum setting for this file. Also it's rather surprising that he couldn't get audio output to speakers at the same time he was scoping the file from the output jack. I have no problem doing this with my desktop system. I suppose this depends on the headphone jack arrangement. Maybe his HP jack turns off the speakers; my front panel HP jack doesn't have to do that if I don't want it to.

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #223 on: March 01, 2015, 12:29:36 AM »
OK, I am taking a break from cleaning this nasty arse desktop PC to format and load Ubuntu on for the lab stuff, and all that... came back over to check the thread and  :o

I made a list of things to try, and I am going to start with checking the ground for resistance/continuity,
then get it warmed up, set XY no input, set to ground, check focus, and tweak astig if necessary (no improvement, back to initial setting)
(start vid)
then do the LINE test using my PCFG w same sq wave settings as cal loop w/ 1 channel only.
then I'm going to put CH1 on cal loop, upper half to start, then add in the PCFG CH2 bottom half w/same freq etc (triggering off cal loop)
anything else?

Let me know if you think that the +55V rail that I adjusted per manual instruction (first part first section of calibration, I believe it is) is causing me these issues, or if you want me to set it back to 55.14V anyway and check.  'twould be easy enough if it may solve my issues.

so from my understanding of connections thus far, If my laptop had a ground on it's plug and a proper connection from charger to PC, I technically don't need to have the "reference" clip connected, is that right?  If so, that would mean a laptop PC should be just fine for using as a FG when unplugged, even, as long as I have a good connection to the laptop's 'chassis' ground (or ground on HP jack collar, same thing) w/ the reference clip.

I will check back before I start the vid once I turn my laptop back on. Can't remove the battery for this test though, or I would do that, too, so there would be no power source other than the PC clock button cell on the MB.

You know, I vaguely remember actually getting fairly good looking square/triangle/sawtooth waveforms from the PCFG the first time I got the PCFG working.....  I don't know what could have changed from then to now.. other than me. so I shall try this again from sq 1..

Offline Pirate88179

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Re: Test Equipment: Oscillocopes
« Reply #224 on: March 01, 2015, 01:12:45 AM »
It's interesting that Dave's Hameg analog scope shows the text backwards, like my 2213a does, but the Agilent shows it the right way around. I wonder why that is. I can't get mine to display the text frontwards by inverting the CH2 (y) channel, or by swapping L and R (this makes the text run up and down instead of across). So maybe he has a way to invert the CH1 (x) channel on the Agilent and this is the cause. It's a mystery to me for sure.

I'm also wondering if that's the best display that the Rigol could do. It's supposed to be able to do some huge number of waveform samples per second, I thought, so I expected the display to be better than that. Maybe he has the sample rate at some non-optimum setting for this file. Also it's rather surprising that he couldn't get audio output to speakers at the same time he was scoping the file from the output jack. I have no problem doing this with my desktop system. I suppose this depends on the headphone jack arrangement. Maybe his HP jack turns off the speakers; my front panel HP jack doesn't have to do that if I don't want it to.

TK:

I am glad you noticed that the lettering was correct on Dave's digital scope.  I thought I saw that as well.  My new pc, if using the headphone jack on the front, disables the speakers of which I am running a total of 11 including a sub.  (All of my speakers except one pair have their own amps including a 100 watt/channel driving my 12" Cerwin Vegas in the living room.)  I can take or tap into one of the line outs on the back and still hear the music.

What the hell is a flac file?  I mean, I know what it is...I looked it up...but have not downloaded any program to open such a file.  I have used some of the choices given in the past and, my problem is, they take over every audio file and you have to use their program to play anything.  Should I just convert the youscope file to mp3?

I thought you would enjoy Dave's video on this.  He really had to manipulate that digital scope to get it to look right, and it still did not look as good, in my opinion, as the older model, ha ha.

Bill

 

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