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'[EE]: viewing non-periodic waveforms with an analo'
2002\04\18@212417 by Donovan Parks

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Hello,

I have a Tektronix 465 analog scope and it works wonderfully for viewing periodic signals.  I've now come to the point where I need to view a 40kHz square wave that lasts for only three periods (and thus is non-periodic).  I can set the scope to single sweep mode and get it to trigget on the first rising edge, but the signal disappears far to fast for me to analysis it.  Turning the time base down doesn't help as the width of the signal shrinks in proportion.

Is there any way to use an analog scope to view this waveform? Would a digital scope solve my problem (I could at least try and capture the screen with a digital scope)?  What do others do when trying to observe non-periodic waveforms?

Thanks,
Donovan

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2002\04\18@214044 by Bob Ammerman

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How often do you get the three cycles of  40kHz ?

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Donovan Parks" <spam_OUTdparksTakeThisOuTspamUVIC.CA>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Thursday, April 18, 2002 9:21 PM
Subject: [EE]: viewing non-periodic waveforms with an analog scope


Hello,

I have a Tektronix 465 analog scope and it works wonderfully for viewing
periodic signals.  I've now come to the point where I need to view a 40kHz
square wave that lasts for only three periods (and thus is non-periodic).  I
can set the scope to single sweep mode and get it to trigget on the first
rising edge, but the signal disappears far to fast for me to analysis it.
Turning the time base down doesn't help as the width of the signal shrinks
in proportion.

Is there any way to use an analog scope to view this waveform? Would a
digital scope solve my problem (I could at least try and capture the screen
with a digital scope)?  What do others do when trying to observe
non-periodic waveforms?

Thanks,
Donovan

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2002\04\18@215122 by Jim

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... that's what they built 'scope hoods' for ...

Seriously - turn the lights down low, concentrate on
just those particulars of the waveform you are measuring
(amplitude - does it pass above or below known voltage
reference points on the CRT, time - does it exceed
or fall short of the expected period) and note if this
non-periodic waveform meets that criterion. This may
take a number of attempts, but lacking a digital
storage scope this has been the tried and true technique
used in the past ... based on the fact that (most!) all
CRTs exhibit some 'persistance' (or lingering luminosity
of the display) due to the 'trace' that details the
waveform.

I don't recall if the 'old' Polariod scope cameras
(with the shutter held open) were any good/fast enough
at capturing these kinds of waveforms or not ...

Jim


{Original Message removed}

2002\04\18@220504 by Barry Gershenfeld

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At 08:28 PM 4/18/02 -0400, you wrote:
>How often do you get the three cycles of  40kHz ?
>
>Bob Ammerman
>RAm Systems
>
>{Original Message removed}

2002\04\18@221351 by Andrew Warren

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Donovan Parks <PICLISTspamKILLspammitvma.mit.edu> wrote:

> I have a Tektronix 465 analog scope and it works wonderfully for
> viewing periodic signals.

   Yep, the Tek 465 is the oscilloscope equivalent to the DC-3.
   It'll probably continue to work wonderfully forever.

> I've now come to the point where I need to view a 40kHz square wave
> that lasts for only three periods (and thus is non-periodic).
> ...
> Is there any way to use an analog scope to view this waveform?
> Would a digital scope solve my problem (I could at least try and
> capture the screen with a digital scope)?

   A storage scope (digital OR analog) would solve your problem;
   I've seen them (and placed them) on Ebay for not a lot of money.

> What do others do when trying to observe non-periodic waveforms?

   I flip the switch on my Tek 2230 scopec from Analog to Digital.
   Works great.

   -Andrew

=== Andrew Warren -- .....aiwKILLspamspam.....cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2002\04\18@221410 by John Dammeyer

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Quite honestly I bought my Tek TDS3032 after having similar problem with
my analog 30MHz Gould no longer being adequate.

If you know it's just a digital wave form you could work up a simple
logic analyzer module that used a rising edge as the trigger and then
wrote the values of the input into a shift register that clocked the
data into a byte wide RAM.  Once the RAM is full put the circuit into a
loop where it reads the RAM and spits it out serially again and put that
to your analog scope.

A few GAL devices or some CMOS 4000 series counter chips will do the job
easily.

John


> {Original Message removed}

2002\04\18@222539 by Bob Ammerman

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Point a video camera at the screen, tape it and freeze frame the result?

This will only work if the waveform occurs while the CCD is capturing the
image.

Bob Ammerman
RAm Systems


{Original Message removed}

2002\04\18@222723 by Jim

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   "Yep, the Tek 465 is the oscilloscope equivalent to
    the DC-3. It'll probably continue to work wonderfully
    forever."

I thought the Tek 453/454 series (discrete parts/components) was
the DC-3 of the 'portable' scopes?

No, wait!

I thought the Tek 547/545 series (discrete parts/components albeit
tubes!) was the DC-3 of the scopes?

Jim

(PS. The 465/475 series use proprietary Tek hybrid modules internally ...)


{Original Message removed}

2002\04\18@230801 by Donovan Parks

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Hello,

Thanks for all the great resposes.  I am generating the signal myself, so I
have adopted the advice to just make the thing periodic for testing
purposes.

Regards,
Donovan Parks

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2002\04\18@234153 by John Dammeyer

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That's easier than the logic analyzer approach.  <grin>

John


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2002\04\19@005721 by Vit

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> Point a video camera at the screen, tape it and freeze frame the result?
>
> This will only work if the waveform occurs while the CCD is capturing the
> image.
>
> Bob Ammerman
> RAm Systems

I used a similar setup with my 475A.
If you have a digital camera, set it up on a tripod, and set the shutter
speed to 0.5 - 1s.  Then, switch your scope to "Single Sweep" mode and arm
it.  Now, all you have to do is push the trigger just before you apply the
signal.  This method works best in a semi-dark room.

Vitaliy

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2002\04\19@013409 by Jinx

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> Point a video camera at the screen, tape it and freeze frame
> the result?
>
> This will only work if the waveform occurs while the CCD is
> capturing the image
>
> Bob Ammerman

That works fine - sometimes you need a couple of goes to
get a good one. Turn the brightness way down BTW

(sorry Mr Dilatush)

http://home.clear.net.nz/pages/joecolquitt/davedong.html

Upper picture is a quick tone-burst happened to have been
caught mid-screen. Note the older persistent trace vs the
more recently drawn (night - room lit)

Lower picture is a standing wave, easy, although both traces
were very faint to the naked eye (daylight)

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2002\04\19@042234 by Alan B. Pearce

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>Is there any way to use an analog scope to view this waveform?

No more than you are currently able to do unless you have one with a storage
tube, but the 465 does not have this facility

>Would a digital scope solve my problem (I could at least try
>and capture the screen with a digital scope)?

Yes, this is one of the advantages of a digital scope.

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2002\04\19@060459 by Bob Ammerman

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At 40Khz you could do a pretty good job sampling it with a PIC.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "John Dammeyer" <@spam@johndKILLspamspamAUTOARTISANS.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Thursday, April 18, 2002 10:13 PM
Subject: Re: [EE]: viewing non-periodic waveforms with an analog scope


{Quote hidden}

> > {Original Message removed}

2002\04\19@091221 by Douglas Butler

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> >Would a digital scope solve my problem (I could at least try
> >and capture the screen with a digital scope)?
>
> Yes, this is one of the advantages of a digital scope.

I would say that is what digital scopes were invented for!

Sherpa Doug

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2002\04\19@172316 by Phillip Vogel

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This is what a 'scope camera is for. Typically, the camera uses Polaroid
film, and has a hood that mounts the camera a fixed distance from the scope
screen, while blocking out the room light. You open the shutter and do a
single sweep. Close the shutter, develop the film, and voiala!

Phillip


{Original Message removed}

2002\04\19@185512 by Robert.Rolf

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I do the same thing with a good web Cam pointed at the scope. Works
reasonably well, but not great for fine detail.

There are also some 'PC sound card scope' software packages out there.
Some of the newer sound cards can sample upwards of 48khz in mono mode.

If you can raise the repetition rate for test purposes, that's your
quickest/cheapest solution.

Robert

Phillip Vogel wrote:
>
> This is what a 'scope camera is for. Typically, the camera uses Polaroid
> film, and has a hood that mounts the camera a fixed distance from the scope
> screen, while blocking out the room light. You open the shutter and do a
> single sweep. Close the shutter, develop the film, and voiala!
>
> Phillip
>
> {Original Message removed}

2002\04\20@031548 by Peter L. Peres

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> What do others do when trying to observe = non-periodic waveforms?

Make it periodic using a signal generator or something else suitable as
required. A digital scope will help. 40kHz square wave may be in range for
one of those 'PC oscilloscopes' you can download from the net.

hope this helps,

Peter

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2002\04\20@062524 by Peter L. Peres

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>Point a video camera at the screen, tape it and freeze frame the result?
>
>This will only work if the waveform occurs while the CCD is capturing the
>image.
>
>Bob Ammerman
>RAm Systems

Very good idea! A CCD camera used under low light conditions is in the
integration mode most of the time so the probability to catch the signal
or its afterglow trail is high! I wish I had thought of that. Perhaps
capturing in moovie mode with a PC connected camera (USB etc) will have
the same result if the frame rate is high and the light level low (shade
out all room light using a cardboard mask and turn on the scope reticle
backlight on low - you   may not need that, the trace will illuminate
some of the reticle).

Peter

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2002\04\20@222443 by Jim

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Well, I took a look at a non-repetitive/single-shot waveform
today and indeed in a room with the lights turned down a 465B
scope *will* display a waveform up to and including the top
sweep setting of 20 ns per division. The waveform is weak
but present at 20 ns/div.

The wave form will not be seen if the room lights are on,
however - even 'shielding' the CRT with one hand won't do
it - the room must be dark.

Given three of four 'shots' I can deduce the amplitude
and pulse-width of said single-shot event.

A pulse train of three or four pulses at 40 KHz was rather
straight forward at 10 us per division. Reading the data
bits would take a little practice and I have used such 'cheats'
in the past as a small piece of paper demarking where the 'bits'
that are to be should appear on the CRT ...

Even in the bygone days of 'analog storage scopes' (preceeding
digital storage scopes) this was often the technique used
because of the limitations of the 'writing speed' of most
storage scopes. The biggest use I ever for 'storage' scopes
was in spectrum analyzers when set for the narrowest IF
bandwidths requiring a a sweep rate of one or two seconds/div
im order to observe 60 or 120 Hz 'sidebands' due to power
supply ripple on a transmitted TF carrier ...

Jim


{Original Message removed}

2002\04\22@094423 by Lawrence Lile

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My analog "storage" scope, which was old enough to vote in the last two
elections, was a "storage" scope because it came with a polaroid camera that
would mount to the screen, blocking out room light.  A little duct tape and
cardboard could make a hood that would mate your camera to your scope.  If
you can get it really dark in there, then open the camera shutter wide,
you'll catch anything that comes across the scope.  This might work best
with an old film camera with lots of manual settings.

--Lawrence

{Original Message removed}

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