Talk:Oscilloscope

Praise

Wow! Great article! Though what's the reference material you guys used? I'd like to submit this to WP:FAC. - Ta bu shi da yu 00:39, 20 Dec 2004 (UTC)

Thanks for your kind words! For the small contributions that I made (primarily having to do with analog storage), I wrote from my own knowledge. My early education came from an excellent series of technical books that Tektronix wrote describing the design of various oscilloscope subsystems, and after that, years of experience using and maintaining (primarily Tek) oscilloscopes.

Atlant 01:12, 20 Dec 2004 (UTC)

You definitely should submit it. I'd been thinking about doing the same thing myself, until I realized I'd better check the talk page first. Dinferno 12:35, 28 May 2007 (UTC)

Aquadag

The electrons, after hitting the screen, must come back to the anode so that the circuit is closed. Otherwise, the negative charge accumulated no the screen will repel the electron beam, preventing it from reaching the screen. The return path of the electrons is provdied by coating the sidewalls of the CRT with carbon particles, referred to as aquadag and by connecting this coating to the accelerating anode. --Krishnavedala 10:57, May 15, 2005 (UTC)

Well, that and the aluminized screen. ;-)

Atlant 17:05, 15 May 2005 (UTC)

Aquadag is (or was) a tradename owned by Acheson Colloids (Corp?) for water-suspended colloidal graphite. Acheson made (and probably still makes) a variety of c.g. products, including Oildag and Alcoholdag. Nikevich (talk) 17:26, 1 February 2009 (UTC)

Cheap 'scopes?

Does anyone have any suggestions as to where a poor hobbyist such as myself might be able to buy an oscilloscope for relatively cheap?

The standard answer used to be Heathkit (or for some, Eico kits), but that option is gone now. :-( That leaves you with the used market, and you can get pretty good 'scopes at reasonable prices if you look hard enough. For example, companies going out of business may sell off their test equipment; that's where my '465B comes from. Another one of my scopes is an older HP military-surplus job that came, believe it or don't, for free from an annual public auction that my town holds to get rid of surplus equipment (from the schools, etc.). Nobody else wanted it so I got it for nothing at the end of the auction.

And, of course, it depends on what you mean by "relatively cheap"; a '2465 still costs a big chunk of change. And at this point, while you can probably get an old vacuum tube cheap, I'd imagine it would pretty hard to keep it up-and-running if you use it often.

Atlant 23:32, 17 October 2005 (UTC)

Well I would suggest Ebay nowadays. Or if you are near to any amateur (ham) radio rallies/auctions, these seem to be places where things go for a song esp if you know what youre looking at/for and maybe can do some minor repairs.--Light current 23:41, 21 April 2006 (UTC).

You can download a free PC oscilloscope for Windows here.--Max 10:03, 23 June 2006 (UTC)

There is another free PC one here --Trounce 14:13, 4 November 2006 (UTC)

Most real work needs more bandwidth than a sound card can deliver, though.

Atlant 11:33, 23 June 2006 (UTC)

Washing your oscilloscope

This is not as crazy as it first appears. As long as the components dont suffer from water or mild detergent damage, this is a good way of removing dust and unremoved flux, nicotine(!) etc that can compromise the circuit boards surface high resistance and crap build up on switches. After washing, its important to let the boards dry out thoroughly, and I recommend placing them near the output of a dehumidifier for about 24 hrs before putting them back and applying volts. I have done this procedure on the plug in boards from a TV set and the set worked perfectly afterwards!--Light current 22:09, 21 April 2006 (UTC)

How do you wash it? Manually in a sink? dishwasher? — Omegatron 23:25, 21 April 2006 (UTC)

No, no of course not a dishwasher. Be serious! You take out all the little pcbs, run them under warm water with some washup detergent using a soft bristled brush to clean away all the muck. If you're sure all parts will stand it, you could use Isopropyl alcohol initially to get rid of greasy/oily/flux/nicotine deposits. Then you rinse thoroughly in clean warm/cold water and let them drip dry before putting them near the dehumidifier for 24 hrs. --Light current 23:33, 21 April 2006 (UTC)

I didnt remove part of your comment intentionally (could have been a mistake)- I thought you had! I must have done ctrlX insted of ctrlC Sorry about that!--Light current 20:52, 22 April 2006 (UTC)

Oh, ok. Running PCBs through a dishwasher is pretty common to remove flux, etc. — Omegatron 20:58, 22 April 2006 (UTC)

Id not heard that one. What solvent do you use to get rid of flux? Maybe a dishwasher is good- but I dont know enough about them to be sure--Light current 21:00, 22 April 2006 (UTC)

You use water-soluble flux, of course!  :-) — Omegatron 18:12, 31 July 2006 (UTC)

Tektronix, in tube (valve) days, told how to wash their 'scopes. It was water and detergent, followed by a distilled-water rinse, then drying at perhaps 160 F. Apparently, the power transformer could be immersed, at least in distilled water. IIrc, they said that the CRT should be removed before washing. Nikevich (talk) 00:11, 1 February 2009 (UTC)

(I posted the above before I discovered that user Atlant is a Tek guy. He really knows!) Nikevich (talk) 17:26, 1 February 2009 (UTC)

Alternatives

rm from page:

Alternatives to the oscilloscope

There is an affordable alternative to an oscilloscope that is useful for many tasks, and perhaps superior for radio repair, and that is to listen to the signals.

The basic plan is to mix (multiply) an intermediate frequency with the signal, and then amplify and listen to the result through a speaker. In other words, you are using amplitude modulation to shift the signal down into the audio band. (For audio frequency signals no modulation is necessary, of course.)

With modern solid-state circuits, such equipment is cheap and can run from a small battery. This diagnostic system was widely used for almost all early radio development, and is still used in Asia, and by impoverished amateur radio operators. In the Soviet Union, the standard radio diagnostic tester combined a multimeter with an oscillator, frequency mixer and audio amplifier that could perform this task.

Or to put it the other way around: An single scope replaces a network analyzer, frequency mixer, delay generator, gated integrator, frequency counter, boxcar avarager

This matl is nothing to do with oscilloscopes but testing methods in general.--Light current 07:27, 28 April 2006 (UTC)

Tek scope caption

This really is too long Atlant. It unbalances the page and the photo. 8-( Maybe most of this info could go in the body of the article?--Light current 04:52, 31 July 2006 (UTC)

It probably should go in whatever section is describing the various function blocks, maybe with some circles and arrows Photoshopped in. If need be, I could certainly shoot some photos of other oscilloscopes (although the odds are they'd be Tek :-), 'cause that's what most of the 'scopes I have access to are! ).

Atlant 13:01, 31 July 2006 (UTC)

Are you suggesting close ups of the various functional areas on the front panel with a small caption describing each one? If so, I think thats a good idea 8-) It doesnt matter that they'll all be Teks. They're probably the best examples to use anyway and my favorite! --Light current 15:25, 31 July 2006 (UTC)

Or a single image with circled areas and call-out lines leading to captions such as "Vertical controls" and "Time base controls", etc.

Atlant 15:54, 31 July 2006 (UTC)

If you like although that sounds like a lot more work to me! And I wouldnt know how to do it 8-|--Light current 16:37, 31 July 2006 (UTC)

I agree that graphics of many different types of controls and explanation of what each does would be great. — Omegatron 18:13, 31 July 2006 (UTC)

Would graphics be better than close up photos of real scopes? 8-|--Light current 18:26, 31 July 2006 (UTC)

Speaking just for myself, I'd prefer the concrete example of the front panel of a real 'scope, suitably disected and labeled. I'll try to cook something up.

Atlant 19:15, 31 July 2006 (UTC)

Agree that real scopes are better. — Omegatron 19:38, 31 July 2006 (UTC)

I've now got a fairly-good photo of a current Tek DPO7254 (2.5GHz Digital Phosphor Oscilloscope) that I'm trying to ready for the article. It would probably mae a better subject for an "expanded" photo, allowing us to have a smaller photo as part of the article's lede. But if the DPO photo doesn't work out, I'll pose and shoot my good-old 465.

Atlant 15:58, 21 August 2006 (UTC)

I have temproarily restored the pic to the large size pending new photos.--Light current 16:01, 21 August 2006 (UTC)

I have made what I hope is a compromise. You can have your huge picture, but not at the top of the article where it squeezes out the text, and where the reader won't understand the caption because the terms haven't been explained yet. The huge picture with the huge caption belongs lower down, where it can be explained in depth. I'm sorry about the two copies of the same photo, but that can easily be fixed. --Heron 20:46, 21 August 2006 (UTC)

Sorry Heron it was not I who placed the picture thus!--Light current 00:01, 22 August 2006 (UTC)

Bandwidth record

The article currently contains the following text:

The current bandwidth record, as of February 2005, is held by the Tektronix TDS6000C oscilloscope family with a digitally enhanced bandwidth of up to 15 GHz and costing about US$150,000.

But Tektronix currently sells a 'scope (the TDS8200 family) which has a sampling bandwidth ranging up to 70 GHz (and it's possible other vendors may go faster; I haven't looked). So shouldn't this sentence be modified to state something like "real time bandwidth" or "non-sampling bandwidth"? (FYI: That TDS6154 manages 40 GS/s across two channels!) And as of 2006, is this Tek still the fastest?

Atlant 22:46, 31 July 2006 (UTC)

Scope picture

C'mon 'O', how many people know how to select the proper thumb size?--Light current 23:59, 21 August 2006 (UTC)

Merge from Dual beam oscilloscope

I don't see any need to have a separate article for dual beam oscilloscope, and as the existing article dual beam oscilloscope is quite short, it would make good sense to implement the proposed merge. DFH 19:18, 26 September 2006 (UTC)

Agree merge--Light current 10:48, 21 November 2006 (UTC)

Thanks for agreement. Merge now done. DFH 19:22, 21 November 2006 (UTC)

Curve tracers

I had intended to create an article about curve tracers, but as yet, I have been too busy. If anyone else would like to take up this task, I would be only too pleased. DFH 19:41, 21 November 2006 (UTC)

I've substantially expanded an existing article. See Semiconductor curve tracer. Feel free to take it farther; it certainly needs the addition of a modern-day picture (which I'll shoot if I get a chance, but feel free to beat me to it).

Atlant 00:54, 28 November 2006 (UTC)

Why are curve tracers so damn expensive cf ordinary scopes?--Light current 00:59, 28 November 2006 (UTC)

Curve tracers are substantially more complex (consisting of an oscilloscope plus a bunch of high-capability, automated power supplies and miscellaneous measuring gear) and they have a much more limited marketplace, limiting the potential volumes and the resulting economies of scale. There's probably also an element of "what the market will bear". I was looking at our Sony/Tektronix curve tracer the other day and noticed it had a CRT with a custom "internal graticule" and I wondered what that custom CRT alone must have cost Tek.

Atlant 01:10, 28 November 2006 (UTC)

Well Atlant Im sure you or I could quite easily design ramping voltage and current sources as a small add on for a normal scope. In fact Im sure Ive seen home brew projects published to do it. After that you only needa low BW scope. So I tend to go with your latter reasons instead of the former!

BTW are you sure about this piece of the article?>

The main terminal voltage can often be swept up to several thousand volts with load currents of tens of amps available at lower voltages.

8-)--Light current 01:15, 28 November 2006 (UTC)

I'm sure about the "several thousands of volts"; that same Tek/Sony curve tracer can do 2,000 volts! I'll verify the current claim.

Ahh. here we are: 10 amps on the particular model I was thinking about.[1]

Atlant 02:04, 28 November 2006 (UTC)

OK. Its just that I dont remember the old Tek 575 tracer going very high in volts or current. But its been a long time since Ive seen one! If you look at the photo on the page, youll see that the volts/div goes upto 20, giving about 200v max, and the current per div goes up to 1000mA/div ginig 10 A max. But perhaps theres a multiplier that is brought in somewhere?--Light current 02:07, 28 November 2006 (UTC)

And if you really want to cook, howzabout 400 Amps pulsed power and 3KV? [2]

Atlant 02:12, 28 November 2006 (UTC)

Yeah certainly looks like a cooker. Good for cooking eggs & ham!--Light current 02:14, 28 November 2006 (UTC)

I really should have explained that I was talking about the S/H market really. Tracers like the 575 are very expensive for what5 they are I feel. Anyway Im not likely to need to use one, so no problem.--Light current 02:18, 28 November 2006 (UTC)

The 400A and 3kV are not simultaneously applied. These are different ranges. DFH 18:58, 28 November 2006 (UTC)

This ap note might aid the MSO segment of the entry

This Agilent Technologies ap note might be a useful addition to the Mixed-Signal-Oscilloscope section. It contains a vendor-neutral description of what an MSO is, and describes how an MSO can be used to debug an 8-bit microcontroller with I²C bus.

1bigdork 22:28, 27 November 2006 (UTC)

faster than the speed of light????

"By the late 1970s, with transistor components rather than vacuum tubes, Tektronix was selling oscilloscopes on which the signal trace traveled across the screen faster than the speed of light."

I mean, Tektronix built great stuff, but defying the laws of physics? I am not editing because I think this might be a malformation, so wanted to ask first...--Cerejota 16:00, 4 December 2006 (UTC)

It's a true claim. It's also a sort of inside joke. When the electron beam sweeps across the screen, there's no physical object that's actually (physically) moving very fast. The electrons are the only thing that's physically moving, travelling at their relatively-leisurely velocity from cathode to screen, with each impinging electron producing a little flash of light. And, of course, the beam is sweeping, with the trajectory of the electrons being varied with time.

It's only that trajectory that, at the screen, moves faster than light. And it's not a physical entity, so it's not constrained by the Speed of Light.

Think of a water hose and nozzle. As you sweep it from side to side, the place that gets wet can move very fast, much faster than the water droplets themselves are moving. It's the same thing here. Or, if you like, think of you aiming a laser pointer at an astronomical screen a few thousand kilometres away; the spot you create on that screen can move much faster than the speed of light.

Your average 'scope screen is 10 cm (0.1 M) across in the X dimension. Light travels at 300,000,000,000 metres per second so about 3.3 ns per metre so about 33 ps per cm. If the aggregate effect of the horizontal sweep and the vertical deflection is moving the illuminated spot on the screen faster than that, the spot is "moving" faster than light. And the fastest calibrated sweep speed of the Tek 7104 'scope was 200 ps/cm, so with some vertical deflection added in...

Atlant 16:15, 4 December 2006 (UTC)

1. No sir ! The laser beam would bend. The coherent light of a laser beam isn't low velocity water droplets. If one sweeps the beam towards a "screen a few thousand kilometres away" the laser beam cannot accelerate beyond the speed of light, it will just take more time to reach the "screen".58.166.39.216 05:25, 8 March 2007 (UTC)

advanced features of oscilloscope

hi if somebody could help me out on this .... this is my library research project... my email id is: mohit AT rome DOT com.ill be highly obliged. thank you

well, I'm afraid the very object of school research work is to get you to do the research work... CyrilB 21:57, 19 February 2007 (UTC)

Links to circuits

I think there are not enough links to circuits used in the scope. Delays, ramps, variable amplifiers, samplers, triggers. Or do I just miss them, I think I have seen ADC at least? Arnero 13:51, 13 March 2007 (UTC)

Some circuits found in 'scopes were called "pulse circuits" some time ago. Nikevich (talk) 17:26, 1 February 2009 (UTC)

makers

I guess their are not too many old timers arround.

(I'm one; will be 73 at the end of 2009.02 Been a 'scope nut almost all my life. Nikevich (talk) 17:26, 1 February 2009 (UTC))

I started trying to find makers and noted that many of the test equiment firms Don't have a Wikipedia presence. Other brands that come to mind is B&K Dynascan, (and the B&K Televison anayist should be decribed also :) (Perhaps as part of Flying spot scanner )) PACO, Hicock, .... cmacd 14:39, 5 June 2007 (UTC)

Before Tektronix, DuMont (Allen B. DuMont Labs.) was the top manufacturer in the USA. (Google on [Allen B. DuMont]; naturally, the first reference is to Wikipedia.) It was Hickok, btw. Nikevich (talk) 00:20, 1 February 2009 (UTC)

Digital scope inventor?

This article claims:

"The first Digital Storage Oscilloscopes (DSO) was invented by Walter LeCroy (who founded the LeCroy Corporation, based in New York,"

However - the earliest references to a Lecroy Digital Oscillscope seem to be 1985. See: https://www.fundinguniverse.com/company-histories/LeCroy-Corporation-Company-History.html http://www.hmi.de/events/SEI/archiv/2003-03/vortrag/wiegard_lecroy.pdf

The earliest complete combination analog/digital oscillscope was the 1980A/B. It is detailed in the Sept. 1982 issue of the Hewlett Packard Journal. http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1982-09.pdf

It seems incorrect to claim the Walter LeCroy invented the digital oscilloscope.

192.25.240.225 00:11, 13 September 2007 (UTC)MikeB

I concur that this is incorrect. Hiro Moriyasu of Tektronix should be credited with this invention.

The same paragraph credits LeCroy with having the highest-bandwidth digital scope. This is misleading, because this refers to a sampling scope. Sampling scopes lack the triggering, single-shot, and real-time signal viewing required by most engineers to be a true DSO. In the real-time scope world, Tektronix holds the nominal bandwidth title at 20 GHz, but this claim is disputed by both LeCroy and Agilent because they cannot verify that a 20GHZ sine wave is attenuated less than 3dB. The LeCroy and Tektronix scopes probably have comparable max BW @ 18GHz. Note: I do not work for either of these companies. -- 1bigdork —Preceding unsigned comment added by 1bigdork (talk • contribs) 03:33, 17 January 2008 (UTC)

True or false information in this edit?

I found this edit from an IP today, "Lissajous figures are an example of how an oscilloscope can be used to track phase differences between multiple input signals." is that edit really incorrect?, or is it just misstaken for a vandalism? Please motivate why false/true. —Preceding unsigned comment added by Electron9 (talk • contribs) 21:39, 14 November 2007 (UTC)

This was the existing text. The anon IP swapped it from some different text; I replaced it. It is correct. Oli Filth^(talk) 22:21, 14 November 2007 (UTC)

Yes - lissajous do measure the phase between two signals. The scope should be in XY mode, and the signals should be of the exact same frequency (normally originating from the same source). If the phase difference is zero, the two signals are identical and x=y, which is the equation of a line, which is exactly what is displayed on the scope. If phase difference in 90 deg, a circle is formed, and if phase difference is 180 degrees, x = -y and a line of negative slope is displayed. See Lissajous[3]. 71.214.54.167 (talk) 02:46, 15 December 2007 (UTC)MikeB

Oscillograph - copying cites from offsite PD copy of PD text?

I've found some off-site references to the early 1875-1915 Joubert and Duddell oscillographs, which interestingly are from public domain sources like the 1911 Encylopedia Brittanica. However, I have no idea how copyright rules apply to a website which has itself just duplicated public domain information. Can I freely copy text and references from these off-site articles? I do not know.

Two websites with the same public domain text:

• http://encyclopedia.jrank.org/ORC_PAI/OSCILLOGRAPH.html
• http://www.1911encyclopedia.org/Oscillograph

I will try to find some info on the licensing questions. DMahalko (talk) 14:47, 5 July 2008 (UTC)

Delay lines

There does not seem to be any mention of the all important delay line in the article. Maybe someone should add it--79.76.203.9 (talk) 15:28, 14 August 2008 (UTC)

Do you mean the adjustable trigger delay found on dual-beam oscilloscopes? How important it is depends on what kind of waveform one is examining, but it is mentioned in the article. Cuddlyable3 (talk) 18:33, 4 September 2008 (UTC)

I've added a description/commentary about the analog delay line in better CRT 'scopes, why it's there, and how its constructed. Alos added text describing delayed sweeps. Nikevich (talk) 17:26, 1 February 2009 (UTC)

FFT feature

Some oscilloscopes have additional analysis tools built in. These may include a Fast Fourier Transform (FFT) feature, which displays the frequency spectrum of the input waveform. It is worth adding this to the Other features section? And does anyone know if there is a simple discussion it could link to, on the characteristics of the FFT spectrum, such as bandwidth, resolution, magnitude and phase? -- Cheers, Steelpillow (Talk) 07:48, 4 September 2008 (UTC)

I'd like to know, too! I had that in mind, but left it perhaps a tad too generic. Nikevich (talk) 17:26, 1 February 2009 (UTC)

Moved Comment From Article

This was in the article, I moved it here. "Note: There is an error in the picture below. The picture notesas an AM signal is not an AM signal. The peaks and valleys should be at the same time on the top and bottom of the carrier."

It's the sum of two sinusoids, one with a frequency much higher than the other. It is definitely not AM. I rewrote the caption. AM would be the product of the two; the lower border would be a mirror image of the upper. Nikevich (talk) 17:26, 1 February 2009 (UTC)

I have no idea whether it's valid or not Terrx (talk) 23:41, 23 September 2008 (UTC)

Reorganization of article

Should the history section be at the top after the introduction? That seems to be the default format of most articles, to provide the history of the subject in question before actually going in to describe the details and nuances. Kortaggio (talk) 22:00, 26 October 2008 (UTC)

I like that, because I'm a history-of-technology nut, but am not so sure others would like it. Nikevich (talk) 17:26, 1 February 2009 (UTC)

Parked here till I can move the non-redundant parts to Oscilloscope

The beam can be moved much more rapidly, and it is easier to make the beam deflection accurately proportional to the applied signal, by using electrostatic deflection as described above instead of magnetic deflection. Magnetic deflection is achieved by passing currents through coils external to the tube; it allows the construction of much shorter tubes for a given screen size. Electrostatic deflection, however, can only swing the beam over a relatively narrow angle, making the CRT quite long for a given screen size. Circuit arrangements are required in magnetic deflection to approximately linearize the beam position as a function of signal current, and the very wide deflection angles require arrangements to keep the beam focused (dynamic focusing).

Some oscilloscope CRTs have geometry-correcting electrodes is their electron guns, as well as deflection plates with contoured front (screen) edges for geometry correction.

Typical oscilloscopes have an input, often referred to as the z-axis, for modulating the beam intensity (brightness). This requires only minimal circuitry.

In principle either type of deflection can be used for any purpose; but electrostatic deflection is best for oscilloscopes with relatively small screens and high performance requirements, while a television receiver with a large screen and electrostatic deflection would be many meters deep. Moreover, electrostatic deflection can operate up to 1 GHz, while the inductance of magnetic-deflection coils limits their practical upper frequency to less than 1 MHz, if even that. Fewer turns of wire means a lower inductance, but also a higher current for a given amount of deflection, so deflection amplifiers for fast magnetic deflection become impractical.

Hewlett-Packard developed a large-screen electrostatic-deflection X-Y display, with a Z-axis (intensity) input as well. Its CRT was unique, in that it had electrostatic deflection, but over a wide angle much like that of magnetic-deflection CRT's. As a consequence, the CRT was not much longer from screen to connector pins ("base") than a magnetic-deflection CRT. It had no deflection plates in the conventional sense, instead what H-P called an electrostatic deflection yoke. This had electrodes inside a glass cylinder, perhaps the neck itself, or else a separate piece. The electrodes were deposited metal in an unusual pattern, like stripes -- rings -- going around the inside of the cylinder. Stripe width varied smoothly with location around the cylinder, offering maximum area top and bottom for vertical deflection, and similarly at the sides for horizontal. There were a few stripes, alternating along the neck's axis between holizontal and voertical deflections.

The deflection amplifiers had quite-good frequency response for small signals, permitting small fine detail to be displayed, but large beam swings turned on boost transistors to provide the larger currents needed temporarily to charge and discharge the yoke and its wiring. The display was described in some detail in the Hewlett-Packard Journal; unfortunately, even the year has been forgotten.

This type of CRT display, called X-Y, is uncommon, and requires external sources of signal to create a trace or image. To prevent burning a spot in the center of the screen, the CRT beam is blanked (shut off) if there are no X and Y deflection signals appplied. The H-P device could serve as an oscilloscope display. There were also short-tube magnetic-deflection X-Y displays, but the frequency response of their deflection systems was essentially only within the audio range.

Some issues must be resolved when using electrostatic deflection. Simple deflection plates appear as a fairly large capacitive load to the deflection amplifiers, requiring large current flows to charge and discharge this capacitance rapidly. Another, more subtle, problem is that when the electrostatic charge changes rapidly, electrons which are already part of the way through the deflection plate region will only be partially deflected. This results in the trace on the screen lagging behind a rapid change in signal, and reduced sensitivity to high-frequency signals. (In fact, at a given accelerating voltage and specific deflection-plate dimensions, there can be no deflection at all for a specific frequency.)

Extremely high-performance analog oscilloscopes avoid these problems by subdividing the vertical (and sometimes horizontal) deflection plates into a series of plates along the length of the "deflection" region of the CRT, and electrically joined by a delay line terminated in its characteristic impedance; the timing of the delay line is set to match the velocity of the electrons through the deflection region. Such a structure is called distributed deflection. In this way, a change of charge "flows along" the deflection plates along with the electrons that it should affect, almost negating its effect on those electrons which are already partially through the region.

Consequently, for a very-fast change in the observed signal, the beam as seen on the screen slews almost instantly from the old point to the new point. In addition, because the entire deflection system operates as an matched-impedance load, the problem of driving a large capacitive load is mitigated. A related scheme using L-C delay lines was used in wideband vacuum-tube deflection amplifiers; several tubes were connected to delay lines for both inputs (control grids) and outputs (plates/anodes). Tube and other stray capacitance thereby became part of the delay-line capacitance, while each tube's gain added ot the total output.

It is very common for oscilloscopes to have amplifiers with two or more input channels. The vertical amplifier rapidly chops or swaps the beam between/among the input channels, blanking the display while switching. This allows the single beam to show as two or more traces, each representing a different input signal. These are properly called multiple-trace (dual trace, quadruple trace, etc.) oscilloscopes. Depending upon the sweep speed, changing channels happens when a new sweep begins (for faster sweeps), or while a sweep is in progress (slower sweeps). In the latter case, the channel-switching rate is free-running, not synchronized with anything. Nearly always the blanked gaps in one sweep are covered by subsequent sweeps, resulting in apparently-unbroken traces.

Much rarer is the true dual beam oscilloscope, whose tube contains an electron gun that produces two independent electron beams, or has two completely-independent electron guns. In the former case, a splitter plate placed in the beam provides two beams. Usually, but not always, both beams are deflected horizontally by a single shared pair of plates, while each beam has its own vertical deflection plates. This allows a time-domain display to show two signals simultaneously. True dual-gun CRTs are harder to make, because the displays from the guns must be aligned acceptably, and CRT mechanical design normally assumes that the electronics that feed the CRT will make needed geometric corrections. Indpenedent rotation of one gun's display relative to that of the other is not practical, electronically. Although rare, multi-gun CRTs have been made in past decades.

Many modern oscilloscope tubes pass the electron beam through an expansion mesh. This mesh acts like a lens for electrons and has the effect of roughly doubling the deflection of the electron beam, allowing the use of a larger faceplate for the same length of tube envelope. The expansion mesh also tends to increase the "spot size" on the screen, but this trade off is usually acceptable.

Although the beam from the electron gun comprises electrons that are fast enough to be useful, most modern CRTs (especially TV and monitor CRTs) apply more high voltage to accelerate the electrons further before the strike the phosphor; this is called post-deflection acceleration (PDA) in electrostatic-deflection CRTs.

--Wtshymanski (talk) 19:09, 14 January 2009 (UTC)

Please do feel free to pester me to merge this! I need to be "pushed". (Looked at your Wiki page, btw.) Regards, Nikevich (talk) 00:29, 1 February 2009 (UTC)

(MANY hours later -- I did an all-nighter! I got carried away (more, as a new topic below). Thanks much for keeping this! I still must come back to gather some of these paragraphs and merge them into the 'scope article. However, I simply wrote up some of the topics anew. Nikevich (talk) 17:26, 1 February 2009 (UTC)

Focus coils in 'scopes? No way!

Referring to the first illustration, I feel safe in saying that no oscilloscope, other than (conceivably!) unique, rare, one-of-a-kind or limited-production, special-purpose 'scopes, ever used magnetic focus. I really hope that a better illustration can be found, because this is a serious, misleading technical error.

(Following paragraph added...) I've been sorely tempted to disable displaying that illustration (that is, leave the URI in the text, but mung it and tell how to fix it.)Nikevich (talk) 17:26, 1 February 2009 (UTC)

(General comment:) While discussing illustrations of CRTs, I've come across a number of them that try to represent a CRT, but (apparently more so in computer-related articles and texts) betray almost total ignorance of reality. Bulb shape and proportions, as well as deflection yokes, are often not in the least representative.

(I apologize for sounding negative!) Nikevich (talk) 00:52, 1 February 2009 (UTC)

Where did such text as that for Focus (early in the article) come from?

It's now part of editing history; I replaced it, totally. It looked like a low-quality, unedited machine translation from a language with a vocabulary very different from that of an Indo-European language. (There wre two or three more. Curious that nobody wanted to edit or change those items.) Nikevich (talk) 17:26, 1 February 2009 (UTC) Sorry; griping, again. Hope to have more-positive remarks, soon! Nikevich (talk) 02:29, 1 February 2009 (UTC)

It came from this edit by an IP which resolves to Madrid. If you think the Focus section was bad, take a look at what the Graticule section looked like before I copyedited it. SpinningSpark 03:09, 1 February 2009 (UTC)

Golly. Spinning spark? I like that! does it refer to rotary spark gaps in the days of wireless telegraphy? (I'm not that old!) I surely have no dislike for Spain, but apparently some well-intentioned soul used a poor-quality machine translator. In one of them, the CRT was called a "pipe". Seemed bizarre, until (as I just now realized) that a pipe is a variety of tube, right? Have brain fade after doing an all-nighter, so I was slow to see the URL. Simply adorable!: "If the control is extinguished the cricket it will not be visible." Translated, "If the graticule light is turned off, the grid lines will not show." "Cricket" is "grillo" in Italian, and the Spanish is probably similar.

Look on my userpage, you should be able to spot what the "spinning" referes to. SpinningSpark 18:10, 1 February 2009 (UTC)

Major rewrite

o Yrs trly has been a 'scope nut, occasionally passionate, for decades, which is his excuse for doing an all-nighter, a major rewrite (although the basic structure was kept). Some parts came through unchanged (especially where I was learning as I read; didn't dare touch those; they were new stuff.) The bizarre machine translations are gone (sorry!). o Added a real bunch of stuff, and the article is, most likely, much too long. o Added: Lots of descriptions of front-panel controls. In maybe three instances, started to explain innards while describing controls, so I moved the descriptions down where they fit better. Now includes variable holdoff and beam finder, for instance.

o Also added explanation of delayed sweep, as well as front-panel controls for it. o Ditto, dual and multi-trace. o Also added text about analog delay in the vertical amplifiers of better 'scopes (also a note above, on this page). Explained what it's for, and how the delay cable is made, and an historic note about the delay lines in Tek. tube 'scopes such as the classic 545A (B?). o I tried to respect the downright peculiar point of view of some author who tried to "force-fit" triggered sweep into the old recurrent sweep way of thinking. 'Fraid my editing ultimately didn't have much mercy, though. It was just too contrived. o Didn't delete much.

There's one downright goofy-stupid-yucky (but not obscene) typo somewhere; sorry. I ran out of steam before a final read-through, and got distracted; lost track of it. There are a few others, I'm sure. If they look truly weird, I use the Dvorak letter layout; love it! (In Dvorak, a few typos that are really easy to make can be baaad.) I'm sorry to leave a few, but there must be somebody who loves to fix such things; I know I do.

I surely don't want to hurt any feelings, but that black computer-graphic 'scope, top left, bothers me. It just doesn't "have it". I have little doubt that it's somebody's Labor of Love, too...

Thanks to Atlant for the big 465 pic! I snagged me a copy.

The job is incomplete; it has some redundant text, and could be better organized. The ToC as it now stands is not thrilling. I also need to merge some of that big bunch of text upstairs (above) into the article.

Some of the historic stuff came from Rider's Scope Encyclopedia (1950); it's hidden in the page source, under Refs. Thoroughly amazing book. (Betcha don't know that the spot at the screen is an image of the crossover just ahead of the cathode. :) )

Not sure whether or not I was doing Bad Things; I embedded quite a few comments, using the < followed by a ! and -- to start them. Are editors permitted to do that? ( )

If somebody hates my leading apostrophe ( 'scope ), feel free to do group search-and-replace. Will probably be all happy in 200 milliseconds.

Btw, is Atlant still here? Sorry I didn't notice he's a Tek. guy until about an hour ago. (I'm definitely a Tek fan; that's only common sense, after all! Agilent isn't bad, but it isn't Tek.) Regards, Nikevich (talk) 17:26, 1 February 2009 (UTC)

Personally, I am not a big fan of using hidden comments to raise questions of reliability etc. It will only ever be seen if someone else decides its dubious and goes in to edit it, at which point it is superfluous. Much better to use a tag template such as {{fact}}, {{who}}, {{dubious}} etc. which will attract the attention of other editors. SpinningSpark 18:19, 1 February 2009 (UTC)