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OT: Oscilloscope Purchase

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  • #31
    You have to buy a lot of digital scope to equal the detail you see with an analog scope. Of course if you need to store waveforms or see a lot of pre-trigger, then digital is it. Even though I have access to some very nice digitals (I work at Keysight), I still use my old 1980B to see fine details.

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    • #32
      Originally posted by Forestgnome View Post
      You have to buy a lot of digital scope to equal the detail you see with an analog scope. Of course if you need to store waveforms or see a lot of pre-trigger, then digital is it. Even though I have access to some very nice digitals (I work at Keysight), I still use my old 1980B to see fine details.
      This is very true..... You can be fooled easily by digital, especially by "aliasing" at the limits of the frequency response.... transients can actually be far different from what you see on digital. Then you want an old analog "storage scope". With those you will spend 10x the time messing around to get to see what you want, but you will get the correct answer if you really need it, at least as far as the waveform. Measurements etc are tons easier on digital, and trigger modes totally blow analog away. You just have to avoid getting fooled.
      2730

      Keep eye on ball.
      Hashim Khan

      Everything not impossible is compulsory

      Comment


      • #33
        One thing I like about the digital scopes (besides the small size and light weight) is the fact that the higher-end models can replace several separate measurement tools, or entire racks of equipment.

        Speaking of high-end, don't forget National Instrument: You can often find their older modules and systems a lot cheaper than the new ones. https://www.ni.com/en-us/shop.html
        25 miles north of Buffalo NY, USA

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        • #34
          Well, I finally pulled the trigger. I ordered a Hantek DSO2D15 plus two 200 Mhz probes from Amazon. I think the included arbitrary function generator took me over the finish line. Now comes the infinitely long wait for delivery. That's OK because I need to clear some space on one of my electronic benches.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

          Comment


          • #35
            Originally posted by nickel-city-fab View Post
            One thing I like about the digital scopes (besides the small size and light weight) is the fact that the higher-end models can replace several separate measurement tools, or entire racks of equipment.

            Speaking of high-end, don't forget National Instrument: You can often find their older modules and systems a lot cheaper than the new ones. https://www.ni.com/en-us/shop.html
            Yup, the lecroy waverunner I picked up a couple years ago has all sorts of features that are software locked, lucky for me someone figured out how to create the activation codes. There are all sorts of things, serial decoders, logic analyzer options (With the USB breakout), basic spectrum analyzers, canbus stuff, and a whole bunch of more special bus interface stuff and eye diagrams.

            The only bad thing about modern scopes is the boot time, sometimes I finds myself just turning on my old Tek 2465 because I don't want to wait for the wave runner. I also have a tiny 7MHz Hitachi battery powered scope with about a 3" CRT, great for stuff where I want complete isolation. It had two 6v lead acids in it, replaced that with a small 3 cell 18650 lithium pack with a boost converter to get the full 12v. Actually runs longer now and significantly lighter.

            I did order one of the national instruments usb based scopes last week for a test fixture, mainly for the ease of integration into labview. We also use the picoscope usb scopes at work and they seem to work well.

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            • #36
              my first 'nice' scope was a b&k 20mhz? dual channel scope... Dad got it from an auction at a tech school. Didn't work. I watched my dad and uncle work on that thing all afternoon (both really good electronic techs..) (probably mid 80's? I don't really remember)

              it ended up being a open 1m ohm resistor that was open.

              we still have it - don't use it anymore. The rigol was the first scope I had with auto.. OMG - I didn't know what I was missing!

              sam

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              • #37
                I could not agree more about the possibility of being deceived by digital scopes. It is commonly thought that the theory behind digital sampling says that any waveform can be reconstructed if it is sampled at twice the highest frequency component in that wave. But a careful examination of what is really being said leads to something a lot different.

                It is a simple and easily demonstrated fact that there are not just two or three or even a dozen or a hundred different waveforms that can produce the exact same samples. There are literally an infinity of them. It is only when you start imposing some restrictions on the original waveform that the number of possible, similarly restricted waveforms is lowered to something manageable. And even then, the one waveform that a scope will display is still reliant on the exact filtering or processing that the output of the digital to analog conversion process. And don't think that these scopes do not convert back to analog. An analog waveform is exactly what is shown on the face of the display. They do not show a scattering of digital points. They interpolate between those points to show a continuous, waveform. Some, if not all of these scopes do allow you to view just such a display of the digital points from the samples. But that is not their normal mode of operation. These deficiencies are most evident when you are talking about frequencies that are near the limit of the scope.

                On the other hand, analog scopes also have their shortcomings when you are near their upper limit of the bandwidth. I have been there many times, staring at a lump or wiggle on the displayed line and wondering just what it really is. And what it was doing in the circuit that I was working on.

                That common misconception about the reconstruction of a waveform is perhaps supported most by the use of digital sampling in audio signals. The human ear is the final target of recorded sound and one of the things that a human ear can not do very well is distinguish between signals where phase shifting has occurred. So a 20 KHz sound wave which is sampled at only slightly more than 40 KHz can sound to our ears very much like the original sound even if it is not a really accurate reconstruction of the original waveform. A sine wave would sound much like a square wave or a triangular wave at that point. And there are very, very few people, if any at all, who could tell the difference in a true, double blind test.

                Unfortunately digital logic circuits can and do react to differences that the human ear will be totally unaware of.

                Frankly, and in my HUMBLE opinion, if you really want to know everything about a waveform and you are using a digital scope, then you need to sample it at a rate that is AT LEAST 10 or 20 times the highest frequency of interest. That's my opinion and I am sticking to it. But, of course, when one is buying his own equipment, there are, there must be some practical considerations. And that is where I am today.



                Originally posted by J Tiers View Post

                This is very true..... You can be fooled easily by digital, especially by "aliasing" at the limits of the frequency response.... transients can actually be far different from what you see on digital. Then you want an old analog "storage scope". With those you will spend 10x the time messing around to get to see what you want, but you will get the correct answer if you really need it, at least as far as the waveform. Measurements etc are tons easier on digital, and trigger modes totally blow analog away. You just have to avoid getting fooled.
                Paul A.
                SE Texas

                And if you look REAL close at an analog signal,
                You will find that it has discrete steps.

                Comment


                • #38
                  Oh, if I haven't said it already, thanks to all of you for helping me with this decision. I don't know if any of the comments here have changed the outcome, but at least I can tell myself that I pushed all the buttons.

                  So thanks very much to all.
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

                  Comment


                  • #39
                    Nyquist says generally you want 4-5x sample rate, anything past that and you start getting to the point of diminishing returns. Plus you start wasting capture memory.

                    Digital scopes will show you a point cloud if you enable it. And in storage mode you can zoom in and see all the points too.

                    One thing to watch out for is many scopes divide up the sample rate among the channels. So on a 4 channel scope that’s rated for 1GS/s you may get 500MS/s in two channel mode and 250 in 4. Then there are cheap scopes that say that are 100mhz but they only have a 100MS/s rate which does not work so hot. They do some averaging to get a waveform but there are many potentials for weird things and aliasing. They are really only good for 20-30mhz.

                    But really I don’t know how many of us here will ever look at signals even close to 20MHz.

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                    • #40
                      Originally posted by macona View Post
                      Nyquist says generally you want 4-5x sample rate, anything past that and you start getting to the point of diminishing returns. Plus you start wasting capture memory.

                      But really I don’t know how many of us here will ever look at signals even close to 20MHz.
                      Last I went up to 26 mHz was around 30 yrs ago, working on a shortwave receiver with an analog scope. The features of the newer digitals are tempting, but quite frankly I'm not familiar enough with their nomenclature, to be confident in buying. Besides the fact that I'm not very active in electronics tech any more. I think more samples/sec is better, correct? But then I see the prices on those scopes and have to check my underpants.....
                      25 miles north of Buffalo NY, USA

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                      • #41
                        Originally posted by macona View Post
                        Nyquist says generally you want 4-5x sample rate, anything past that and you start getting to the point of diminishing returns. Plus you start wasting capture memory.

                        Digital scopes will show you a point cloud if you enable it. And in storage mode you can zoom in and see all the points too.

                        One thing to watch out for is many scopes divide up the sample rate among the channels. So on a 4 channel scope that’s rated for 1GS/s you may get 500MS/s in two channel mode and 250 in 4. Then there are cheap scopes that say that are 100mhz but they only have a 100MS/s rate which does not work so hot. They do some averaging to get a waveform but there are many potentials for weird things and aliasing. They are really only good for 20-30mhz.

                        But really I don’t know how many of us here will ever look at signals even close to 20MHz.
                        What you want for SMPS work is to include harmonics, which means transients, and seeing the edge transition times on gate drives etc.

                        Remember, on ANY scope, analog or digital, if you get close to the frequency limit with the fundamental, you filter off the harmonics. So, if you look at a 20 MHz signal with a 100 MHz 'scope, you see only the first 4 harmonics, the rest are filtered off.

                        When you think about it that way, you quickly see that a 100 MHz 'scope is not an extravagance at all. And the sample rate is easily seen to be important. A 1GHz sample rate translates to a cutoff which cannot be higher than 500 MHz, but at that frequency, you get only one sample..... with 100 MHz, you now get 5 samples per half cycle, which allows at least some semblance of detail. In reality, the 1 GHz sample rate provides detail similar to an analog 'scope up to around 30 MHz, maybe less.

                        Of course, the "sample rate" of the analog scope is related to the cutoff frequency. And it will lie to you by showing you a nice continuous waveform, with a slight bump on it. That "bump" is actually your evidence of a big transient at a frequency significantly above the cutoff frequency.

                        The good news is that you saw it. And that with the analog 'scope, the cutoff is typically more gradual, so things can still be "seen", although the amplitude cannot be trusted in any way, above cutoff. With the digital 'scope, you probably would not have seen that transient at all.
                        2730

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        Comment


                        • #42
                          Originally posted by Paul Alciatore View Post
                          Well, I finally pulled the trigger. I ordered a Hantek DSO2D15 plus two 200 Mhz probes from Amazon. I think the included arbitrary function generator took me over the finish line. Now comes the infinitely long wait for delivery. That's OK because I need to clear some space on one of my electronic benches.
                          why dont i see that on their site?

                          https://www.hantek.eu/oscilloscopes/
                          http://www.hantek.com/products/List/3
                          Last edited by dian; 04-18-2021, 12:10 PM.

                          Comment


                          • #43
                            Originally posted by J Tiers View Post
                            Do you demand "brand new"?

                            Because used ones do offer a far lower price. I bought a Fluke "Scopemeter" portable a few years ago for well within your budget. It is the larger type, with a big screen, digital, with built-in meter, true RMS, the whole nine yards.

                            The trigger options on it are better than the equivalent Tek, and it is isolated for up to 600VAC on each channel, depending on the voltage "category" you need.

                            Far more oscilloscope than I would otherwise have obtained at that price. Only downside is the screen is not color, so you need to keep better track of which trace is what.
                            You saw a scopemeter in the < $500 range? You should have bought it.



                            The thing with the Rigols/Siglents/Hanteks/Whatevers is that they don't have the same level of design rigor, so they will generally have known issues with measurement integrity or performance in some situations. You get extra bells and whistles, but they come with that caveat. Many forums for EE stuff are devoted to documenting the use of these kind of scopes.

                            I want to buy one for myself, but haven't been using my old tek CRT 4-channel scope enough to justify it. If I was going to really buy one, I'd go find a used good condition TDS-2024B, but I do BLDC motor stuff, so having the four isolated channels is a big plus. If there was a store left who sold them locally, I would have bought a Rigol by now. Before they closed, I had gone to Fry's three separate times with cash in hand to buy whatever they had, but they had no stock at the time. Oh well.
                            -paul

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                            • #44
                              Most scopes will go way past their rated frequency anyway. I had a 100mhz Tek TDS series and it would do 250mhz no problem with some attenuation. My lecroy is rated for 600 and does 1ghz before attenuation starts to happen. Though that one is rated 10GS/s. Pretty overkill for home use, I don’t know the last time I looked at anything over a couple hundred kHz. At work we have rf drivers on stuff that’s over 100mhz though.

                              we do use the spectrum analyzers from signal hound, they work pretty well.

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                              • #45
                                Some do go past their limits, but as noted, it is not that useful unless you have sky high sample rates like your 10GS/s. You end up with very little detail, if any, and things just do not look as they should. You end up pushing further toward the basic Nyquist sampling limit, let alone being able to see details.

                                The response is "there" but not very useful.

                                The equivalent with an analog 'scope is very useful. You have a "sampling rate" that is very high.

                                [QUOTE=psomero;n1939155]

                                You saw a scopemeter in the < $500 range? You should have bought it.

                                ............../QUOTE]

                                I did buy it.... it cost me $300 for a 196B, the bigger screen type, and I got some other stuff with it at that price. Took it in to work, where the standard 'scopes" were the similar portable Tek unit, and the Scopemeter was actually considerably more versatile.
                                Last edited by J Tiers; 04-18-2021, 04:33 PM.
                                2730

                                Keep eye on ball.
                                Hashim Khan

                                Everything not impossible is compulsory

                                Comment

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