Input on 1st digital oscllioscope purchase - Page 1
Forum section: electronics / testgear

author: videobruce
author_rank: Frequent Contributor
timestamp: September 28, 2014, 01:04:55 pm
content: Coming from the world of analog scopes which was a number of years ago, when digital scopes first came on the market in force, I remember warnings about some of the misleading specs. Not that any professional manufacture (importer) would try to mislead anyone in the T&M field mind you.Sampling rate I believe was one that can be misleading depending on how it was spec'd.I'm looking for a halfway decent scope, NOT entry level, but not 'lab grade' either. The question is, how much does one have to spend to get a 'decent' model for mostly 'hobby' use that has a at least an average level of accuracy, dependability and stability. I would prefer to stay under $1k US unless that isn't realistic. I see these ones for under $500, but I didn't want to go that low.Battery operation not necessary,Color LCD is,Two channel should be fine (I don't see a need for more)Typical, common control layout, no 'odd' designsI don't need 'lab' precision, but again I don't want the low cost models.Used or demo ok, but I donotwant any boat anchors.Anyone suggest good reading material (online pdf documents for example) to bring me up to speed as I like to digest all of this before the purchase?

author: dr.diesel
author_rank: Super Contributor
timestamp: September 28, 2014, 01:15:19 pm
content: There are a ga-billion threads here on this very subject, read through, you'll find lots of good info. One thing you don't mention, how much bandwidth do you need? Do you need protocol decoding, etc?What kind of signals/projects do you intend on probing?

author: videobruce
author_rank: Frequent Contributor
timestamp: September 28, 2014, 01:31:28 pm
content: I have already started reading through them.From an analog standpoint I would say at least 100MHz. Can't answer the other specific.

author: Fungus
author_rank: Super Contributor
timestamp: September 28, 2014, 02:00:00 pm
content: Quote from: dr.diesel on September 28, 2014, 01:15:19 pmOrders of magnitude more than that (last time I counted....)Quote from: videobruce on September 28, 2014, 01:31:28 pmWithout knowing that stuff, it's a bit like asking "how long is a piece of string?"All advice is useless until you fill in the blanks, you might even end up with a boat anchor!PS:https://www.eevblog.com/forum/testgear/newbies-please-read-before-posting/

author: dr.diesel
author_rank: Super Contributor
timestamp: September 28, 2014, 02:55:48 pm
content: Without knowing more, if you wanna just start playing around, something like the Rigol DS1000s/1100s are hard to beat on price/performance.Maybe something like,this.

author: nixfu
author_rank: Unknown
timestamp: September 28, 2014, 02:57:16 pm
content: As a newbie I would suggest one thing for sure. Get a Rigol.I don't know which model is right for you, but I do highly suggest it's a Rigol.Why? Not because they are the absolute "best" or anything, but simply because they are the most widely used in the Amature community and so you will have LOTS of help, and people to answer questions, there are many many examples to learn from, there are tips and tutorials all over the place etc. As a new guy that might be much more valuable than getting something that might have a few bells and whistles or a few % better specs etc. The community for something like Owan, etc are much much smaller than that of Rigol users. It's somehing importsnt to keep in mind.For 100mhz depending on your budget the older ds1000/1100 series rigols or what appears to be the new best values for your money are probably the brand new 1054z that you can upgrade the 2 channel model from 50mnz to 100mhz with a simple hack MAYBE, or the 4 channel 1074z model that you can upgrade from 70mhz to 100mhz with a hack for sure. I have the 1074z and its a great value.BTW, Dave is supposed to be getting one of the brand new 1054z scopes soon so look for it on eevblog.And don't forget that eevblog members get a 6% discount from tequipment.net which makes the rigols even a better deal from them.

author: frenky
author_rank: Unknown
timestamp: September 28, 2014, 05:42:14 pm
content: fyi ds1054z has 4 channels...

author: Lightages
author_rank: Unknown
timestamp: September 28, 2014, 06:04:01 pm
content: Based on what I have been reading on the forums, and from information from trusted members here, I would get the Rigol DS1054Z and hack it. You get 4 channels, 100MHz bandwidth in one channel mode, fast update speed, protocol decoding, long memory, nice big screen, all for $400 plus shipping. I make this recommendation based on the fact that you aren't sure what you need and this will do almost everything well. It is more than most people need unless you need higher bandwidth.If you need higher bandwidth, then we need to hear about it.

author: nctnico
author_rank: Super Contributor
timestamp: September 28, 2014, 06:14:05 pm
content: Nowadays there is no reason to limit yourself to 2 channels either. Just get a 4 channel oscilloscope.

author: Mark_O
author_rank: Frequent Contributor
timestamp: September 28, 2014, 08:52:41 pm
content: Quote from: videobruce on September 28, 2014, 01:04:55 pmIt's really not, these days.QuoteAt the rate we're going, if everyone thinking of buying their first DSO starts their own thread, we're going to have a lot of redundant topics.The answer to your question of how much one needs to spend, blah, blah, is $399. I'm not sure why you have an aversion to spending less than $500.QuoteYour specs are inadequate to make an informed recommendation. However, if you're not averse to spending more than the minimum, and see no need for more than 2 channels, the DS2000 would be a good choice. Especially since your moniker is 'videobruce', and the DS1000z series video triggers aren't spec'ed to handle more than 576p. In addition to providing extra bandwidth (and lots of other useful capabilities), the DS2000 triggers on HD, to 1080p.

author: nctnico
author_rank: Super Contributor
timestamp: September 28, 2014, 09:00:18 pm
content: I'm wondering where you'll find analog video signals nowadays.

author: Mark_O
author_rank: Frequent Contributor
timestamp: September 28, 2014, 09:34:30 pm
content: Quote from: nctnico on September 28, 2014, 09:00:18 pmVGA, etc. on computers. HD component video outs on consumer gear. It's not ALL gone (yet). Though I'm sure the studios would like it to be.

author: EEVblog
author_rank: Unknown
timestamp: September 29, 2014, 12:17:09 am
content: You mention "accuracy, dependability and stability"All modern digital scopes should have essentially zero stability and accuracy issues.Out of the big names, the clear winner at the low end is Rigol, and their new DS1054Z is unbeatable value. DS1072 if you want more performance, bigger screen, and separate vertical controls that is closer to the $1K mark.Coming form the analog world you want one with a "variable intensity" display that looks and feels like an analog. The Rigol's are excellent in this regard, see here:

author: true
author_rank: Frequent Contributor
timestamp: September 29, 2014, 01:20:03 am
content: Quote from: EEVblog on September 29, 2014, 12:17:09 amI think you typo'd DS2072.But to add content to this post, I agree with what Dave saidDS1054Z hard to beat at $400USD, DS2072 with bigger screen, separated vertical and playback controls really comes in handy for some of the digital or mixed stuff I debug. One is $400 class, the other is $800 class - and if you don't like these, there are others around the $1k mark (usually a bit over) that are nice.In addition to the DS2072 I also have DS1074Z-S and the screen is not a bad size compared to entry scopes of only ~3 years ago.

author: videobruce
author_rank: Frequent Contributor
timestamp: September 29, 2014, 05:45:00 am
content: Thanks for all the input. Sorry for starting another 'scope' thread, but from the few that I have read, I needed more info and didn't want to barge in.QuoteRigol was on my short list already. I know there are popular here and I have had experience with Rigol in the past which supports that as a leading choice. Looking for a make/model of anything I factor in the popularity (or lack of) of the item as much as possible though sometimes you have to look elsewhere.QuoteYou can add CCTV cameras, but that would not be a mainstream use.There are a number of specs that are new to digital scopes I will have to read up on that I won't ask here unless I can't find sufficient data elsewhere.

author: EEVblog
author_rank: Unknown
timestamp: September 29, 2014, 07:24:31 am
content: Quote from: videobruce on September 29, 2014, 05:45:00 amThere isn't much you can do wrong in terms of specs these days. Any scope with MB worth of sample memory is what you want, and 1GS/s sample rate, and pretty much every scope of the market meets that except for Tek's pathetic low end TBS digitals.The other major thing is the variable intensity analog-like display as I mentioned, and not all the cheapies have that, or have it implemented as well as Rigol or Agilent do it.

author: videobruce
author_rank: Frequent Contributor
timestamp: September 29, 2014, 10:32:49 am
content: This "variable intensity", is this what you are talking about?QuoteNot to go OT, but this is exactly where/what I'm having trouble dealing with looking for a spectrum analyzer that I had a hard time explaining in another thread.Since you mention this, "memory depth". How much is enough for between "hobby" use and low end lab grade and what does more get you?

author: Fungus
author_rank: Super Contributor
timestamp: September 29, 2014, 10:53:57 am
content: Quote from: videobruce on September 29, 2014, 10:32:49 amEven the bottom-of-the range DS1054Z can sit there waiting for "runt" pulses and do pass/fail testing (if a waveform goes outside a specified boundary it flags it for you), eg. In this image the single wave that didn't stay inside the black boundary area has caused a trigger:

author: nctnico
author_rank: Super Contributor
timestamp: September 29, 2014, 11:13:04 am
content: QuoteI'm not sure analog oscilloscope simulation is such a good thing. People tend to forget that seeing narrow pulses on an analog oscilloscope was very hard to do. Crank the brightness up beyond sane levels and then hope the spike becomes visible a low sweep rates. A good digital oscilloscope has peak detect which is a much better way to spot narrow pulses than ever possible on an analog oscilloscope. Same goes for finite/infinite persistance modes.

author: videobruce
author_rank: Frequent Contributor
timestamp: September 30, 2014, 06:16:01 am
content: Is this "analog" mode (for lack of a better term) an option on some of these scopes?

author: Fungus
author_rank: Super Contributor
timestamp: September 30, 2014, 06:21:34 am
content: Quote from: videobruce on September 30, 2014, 06:16:01 amNo, it's a standard feature even on the $400 model.

author: EEVblog
author_rank: Unknown
timestamp: September 30, 2014, 06:27:32 am
content: Quote from: videobruce on September 29, 2014, 10:32:49 amEven the cheap hobby ones have just as much if not more than the "lab grade" scopes.

author: EEVblog
author_rank: Unknown
timestamp: September 30, 2014, 06:30:09 am
content: Quote from: videobruce on September 30, 2014, 06:16:01 amIt comes standard with the $399 Rigol DS1054Z and all the above models. The higher models like the DS2000 series have more intensity grading shades though.

author: EEVblog
author_rank: Unknown
timestamp: September 30, 2014, 06:33:54 am
content: Quote from: videobruce on September 29, 2014, 10:32:49 amYes, every manufacturer calls it something different. DPO for Tek for example. Rigol just call it "multiple intensity levels waveform display"Some have a colour intensity, others have mono like an analog CRO.

author: tggzzz
author_rank: Super Contributor
timestamp: September 30, 2014, 07:23:08 am
content: Quote from: EEVblog on September 29, 2014, 07:24:31 amBe aware that a modern 1GS/s scope almost certainly won't let you see a 500MHz signal. (Older digital scopes did; I once used a 1GHz scope to see sub-ns risetimes, but it only did 40MS/s)For digital signals, decide on the risetime of the signals that you wish to see. That will determine the bandwidth of the analogue front end using the standard equation BW = 0.35/tr. For digital circuits 100MHz is probably the lowest you should use, since many circuits have 1ns risetimes and you may well want to see time differences of the order of a few ns.Consider that for digital circuits you might only need a scope to ensure signal integrity. Once integrity is ensured, capture and debug in the digital domain, not the analogue domain.Don't forget to add in the cost of the probes. Be aware that typical *10 probes with a 6" ground lead and a 15pF tip capacitance will self resonate at ~100MHz (and lower if circuit capacitance is added to the calculation).

author: videobruce
author_rank: Frequent Contributor
timestamp: September 30, 2014, 10:25:24 am
content: QuoteIf I didn't know better, thus spec sounds more as a marketing tool just like in consumer electronics where they try a different 'spin' each year to sell something. Example; "LED" TV vs LCD scam Samsung started a few years ago.I found a couple of white papers on memory depth I will take a look at. One is here, the other is from Agilent;http://www.eetimes.com/document.asp?doc_id=1279463.QuoteThis is what I mentioned in the 1st post regarding the sampling rate spec.I have ruled out the 320x240 screens. Actually in this day, 640x480 is outdated AFAIC.

author: videobruce
author_rank: Frequent Contributor
timestamp: September 30, 2014, 10:28:33 am
content: There is also this with Rigol mentioned. I don't know if you guys agree with the response or not;http://electronics.stackexchange.com/questions/76377/what-is-the-importance-of-memory-depth-when-selecting-a-digital-storage-oscillos

author: Fungus
author_rank: Super Contributor
timestamp: September 30, 2014, 10:37:04 am
content: Quote from: videobruce on September 30, 2014, 10:25:24 amHuh? "Sour grapes" springs to mind when reading that - marketing people trying to tell us why their 'scopes don't have as much memory as the competitor.Isn't the best solution to have lots of memory and let the user choose a smaller buffer if he feels the 'scope is bogging down? (Like Rigol does...)

author: nctnico
author_rank: Super Contributor
timestamp: September 30, 2014, 11:31:08 am
content: Quote from: tggzzz on September 30, 2014, 07:23:08 amActually rise time doesn't affect seeing time differences. Even if the risetime of an oscilloscope is 5ns you'll still see a 1ns delay between two signals provided both channels have similar accuracy. In other words: the ability to see differences in timing between 2 channels has everything to do with how well the channels are matched. This should be somewhere in the specification of an oscilloscope.Regarding memory: more is better as long as it doesn't slow the oscilloscope down and the memory is easy to scroll through.

author: tggzzz
author_rank: Super Contributor
timestamp: September 30, 2014, 05:03:12 pm
content: Quote from: nctnico on September 30, 2014, 11:31:08 amTrue, but a faster risetimemakes it easier to accurately discriminate the time at which a threshold voltage is crossedreduces the requirement for the ADCs non-linearities to be matched, and the channel'a analogue response to be matchedThus, in this non-ideal world, a faster risetimeisstrongly positively correlated with discriminating smaller time intervals - even though there isn't a simple direct relationship.

author: Precipice
author_rank: Frequent Contributor
timestamp: September 30, 2014, 05:13:44 pm
content: Quote from: nctnico on September 30, 2014, 11:31:08 amAnd if you particularly care, you'll swap the inputs (and probes) to check...There are too many ways to get errors, not to, and what's on the scope screen isn't always what's at the probe tip (or even at the nodes when the probes are off!)

author: David Hess
author_rank: Super Contributor
timestamp: October 01, 2014, 09:35:22 pm
content: In rough order of importance, the things I look for include:Peak DetectionGraded Intensity DisplayHigh Acquisition RateI am less interested about a long record length but there are some applications which require it.Some applications require 4 channels or logic analyser capability.If the oscilloscope does not support equivalent time sampling, then I would be concerned about sampling errors in the form of non-linearity and jitter in the digitizer but this is not usually specified and nobody tests for it so there is not much to be done unless you have the opportunity to evaluate it yourself. Thankfully like record length, in most applications it will not matter.

author: tggzzz
author_rank: Super Contributor
timestamp: October 01, 2014, 09:50:01 pm
content: Quote from: David Hess on October 01, 2014, 09:35:22 pmWhy do you regard peak detection as being pf paramount importance? What's the "use case" or application?

author: videobruce
author_rank: Frequent Contributor
timestamp: October 01, 2014, 09:51:07 pm
content: Quote from: Fungus on September 30, 2014, 10:37:04 amCan you comment further where you disagree what what was said? I understand there is a sales angle to any of those briefs, but it isn't all 'sales'..QuoteThat was discussed in that paper.

author: nctnico
author_rank: Super Contributor
timestamp: October 01, 2014, 09:56:25 pm
content: Quote from: tggzzz on October 01, 2014, 09:50:01 pmI don't touch a DSO with a stick if it doesn't have peak detect. Long memory or not without proper peak detect you'll miss narrow pulses for sure.

author: David Hess
author_rank: Super Contributor
timestamp: October 01, 2014, 10:23:11 pm
content: Quote from: tggzzz on October 01, 2014, 09:50:01 pmThis comes down to any application where the record length is insufficient to maintain the highest sampling rate at the current time/div setting although there are other advantages even if this is not an issue. Peak detection also makes for an quick sanity check that aliasing is not occurring.

author: tggzzz
author_rank: Super Contributor
timestamp: October 01, 2014, 10:51:14 pm
content: Quote from: David Hess on October 01, 2014, 10:23:11 pmAh, so it is the "peak measured value within the displayed sample interval".It isn't clear to me under which circumstances that non-linear algorithm is/isn't the most appropriate. I suspect that for many purposes the mean value might be a more appropriate algorithm, and that using the peak could have some unexpected and subtle side-effects.I need to ponder, but I'm not sure I'll come to firm conclusions.QuoteWith a conventional analogue scope, aliasing wouldn't be invisible, since the trace would just appear noisy or blurred. Strike one against naive digitisation.Perhaps if measured samples (5.0, 4.9, 5.1, 5.0. 4.9, 5.1) are all within a single displayed sample, the displayed sample should be a 4.9V-5.1V smudge, rather than a single value 5.0V(mean) or 5.1V (peak) point.

author: David Hess
author_rank: Super Contributor
timestamp: October 02, 2014, 04:33:35 am
content: Quote from: tggzzz on October 01, 2014, 10:51:14 pmCRTs have a "writing rate" which could in theory limit the ability to show fast glitches but I have never seen it occur. This is one of the advantages of using a high bandwidth analog oscilloscope even in lower bandwidth applications; they have faster CRT writing rates which goes along with brighter and clearer CRTs.QuotePeak detect returns a pair of values for each sample point in the record so the record length is usually halved. Some DSOs display a single point if all of the values are within a small range of each other which has the effect of removing noise.I have not had an opportunity to do detailed tests on a modern DSO with a graded index display so I have no idea how they operate but Ihaveseen them miss glitches without peak detect mode so something is different. We had a discussion about what theyshoulddisplay if not simple index grading here months ago but it had more to do with accurately displaying noise rather than peaks. There are all kinds of clever things which could be done which are decidedly non-analog like.

author: tggzzz
author_rank: Super Contributor
timestamp: October 02, 2014, 10:38:22 am
content: Quote from: David Hess on October 02, 2014, 04:33:35 amThis is a most interesting discussion, and I'm going to follow up that search term.One of my current projects is to build a cheap, very fast scope which will have some decidely strange characteristics in order to accomodate fast+cheap simultaneously. It will necessarily have something akin to a graded index display even for fast waveforms. I am aware that I haven't considered how it would work with slower waveforms, and this will force me to concentrate my mind. OTOH I might decide that the sole raison d'etre for the scope is speed, and, in the short term, merely ignore the issueThanks

author: nctnico
author_rank: Super Contributor
timestamp: October 02, 2014, 11:00:52 am
content: Quote from: tggzzz on October 01, 2014, 10:51:14 pmThe reason you need peak detect is that in many cases you want to see whether there is a pulse somewhere in the signal. If the signal is undersampled then you'll miss those peaks. An example is looking at vsync signals. These are very short compared to the period.Just averaging the signal is asking for trouble because you basically miss all the HF information.

author: tggzzz
author_rank: Super Contributor
timestamp: October 02, 2014, 11:09:03 am
content: Quote from: nctnico on October 02, 2014, 11:00:52 amHaving done a little research, I now have a better understanding of what's being done - and yes you are correct, of course.In particular, I found these pictures informativehttps://www.eevblog.com/forum/testgear/oscilloscope-specs-which-are-really-important/msg181637/#msg181637

author: David Hess
author_rank: Super Contributor
timestamp: October 02, 2014, 01:53:50 pm
content: Quote from: tggzzz on October 02, 2014, 10:38:22 amThe short discussion came about in connection which how an analog oscilloscope can be used to accurately measure the RMS value of wide bandwidth Gaussian noise which is usually a rather difficult thing to do requiring a specialized instrument like a sampling or thermal RMS voltmeter. DSOsshouldbe able to measure it directly using the same techniques that sampling RMS voltmeters use but some work better than others doing this. What no DSO can do is duplicate how an analog oscilloscope does it and they work every time. At least I have never seen or heard of one which can do it.I doubt the above technique, tangential noise measurement, is feasible or even desirable in a DSO but it led to a short discussion about *how* a display which is not exclusively index graded could produce the same result. (*) My thought was that such a display could also show detected peaks without compromising index grading.For myself, all of my DSOs are old and slow and lack index graded displays but they do have peak detection and oddly enough very high display resolution which makes up somewhat for their other shortcomings. "Retina displays" existed in DSOs about 30 years before Apple came up with the term.Producing an index graded display record during decimation would preserve display quality and high waveform acquisition rates at the expense of record length. I think Tektronix wrote some white papers discussing this and how their early "digital phosphor" oscilloscopes worked. I wonder if this can be done inexpensive with an FPGA based design. I know Rigol is not doing it this way. This is in contrast to display generation from long record lengths so has little advantage as far as specmanship and marketing.(*) Technically index grading is not required to do tangential noise measurement. A halftone display produced via variable dot density like you would find in an analog sampling oscilloscope is sufficient.

author: nctnico
author_rank: Super Contributor
timestamp: October 02, 2014, 02:38:56 pm
content: About a decade ago I embarked on designing my own USB oscilloscope. PC memory was already cheap so I opted to put 2GB of memory on it which provides enough storage for 1Gpt/s per channel. In that design I kept the sampling frequency constant and have the FPGA process the data (average + peak detect) into display data on the fly OR I could replay the stored waveforms from the FPGA to create the display data.