Do I really need a 4 channel scope? - Page 1
Forum section: electronics / testgear

author: nbritton
author_rank: Frequent Contributor
timestamp: September 16, 2015, 11:47:51 pm
content: I'm still mulling over what scope to buy and now I've come to the trouble of deciding how many channels I need. I'm fairly certain I'm going to get a MSO model that has 16 digital channels. With all those digital channels is there really a use case for needing 4 analog channels? The primary purpose for this scope is working with digital circuits, however I do also like to play with analog. What will I not be able to do with a 2 analog + 16 digital channel scope?Wytnucls stated in another thread: "If you don't know if you need a four-channel scope, you don't need one."I'm inclined to agree with this, I don't really see a use case for a 4 channel analog scope that can't also be handled by 2 analog + 16 digital channel scope. I just wanted to double check, since I'm new at this, before I go off half cocked buying a 2 channel scope like the Rigol MSO2072A.

author: dadler
author_rank: Unknown
timestamp: September 16, 2015, 11:50:11 pm
content: When you do need them, you need them.However, I find myself using only 2 channels most of the time. It really depends on your use case.Some issues are nearly impossible to debug with only 2 channels. Most are not.

author: mos6502
author_rank: Frequent Contributor
timestamp: September 16, 2015, 11:52:07 pm
content: Depends on what you're doing.Let's say you're designing a DC-DC converter and you want to simultaneously monitor power in and power out ... there's your four channels.If all you want to do is check if a pin on your Arduino is wiggling ... you don't need four channels.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 17, 2015, 12:03:48 am
content: Quote from: mos6502 on September 16, 2015, 11:52:07 pmOk, that's a valid use case. However, as a 'hobbyist' do I really need to 'simultaneously' monitor power in and power out? Couldn't I get by simply measuring them one at a time?

author: dadler
author_rank: Unknown
timestamp: September 17, 2015, 12:39:37 am
content: Quote from: nbritton on September 17, 2015, 12:03:48 amThe correlation of simultaneous signals is where more channels is most valuable.Say you're feeding an analog signal into a circuit (which you want to monitor/correlate), doing some communication via SPI (say you have an I2C/SPI ADC/DAC), and generating some output signal (which you want to monitor/correlate as well).You can use digital channels to look at SPI data, but what if the signals aren't clean and you need to verify signal integrity? Or you need to monitor peak current across a trace, or track down noise/crosstalk?You can use up two channels very quickly.The DS2000 is a nice scope though. Perhaps go for it, and if you decide down the road you need 4 channels, pick up a DS1054Z as an extra scope. You can use the external trigger on the DS2000 to correlate the two scopes and have 6 channels available.

author: JoeB83
author_rank: Regular Contributor
timestamp: September 17, 2015, 01:35:05 am
content: As mentioned by others, it depends what you're doing.I'd say it's generally a good idea. When I started doing electronics, the first thing I built & worked on were audio amplifiers. Having one channel monitoring the signal fed from the function generator and one each monitoring left and right channel output used up three channels right away. Diagnosing multiple or bipolar power supplies pretty much requires four channels too.I'd say go for it if at all possible.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 17, 2015, 10:46:21 am
content: Id say nowadays is way more useful having a four analog channel scope with a nice screen than a digital analyzer built in the scope. I really find the saleae anaylzers way more usefull than on scopes. All starts with the screen width, the logic analyzer is highly time spread and nom repetitive. With a pc analyzer you can navigate much more comfortably. Id buy a agilent 2000 or 3000 series without anaylzer license.

author: nctnico
author_rank: Super Contributor
timestamp: September 17, 2015, 10:49:33 am
content: Once you have a 4 channel scope you'll never go back to a 2 channel scope. Its true you won't be using 4 channels all the time but I find myself using more than 2 channels quite often.

author: EEVblog
author_rank: Unknown
timestamp: September 17, 2015, 11:11:42 am
content: Quote from: nctnico on September 17, 2015, 10:49:33 amI would not like to have a lab that only has a 2 channel scope.If you can afford a 4 channel scope, get one.It's like having a deep memory scope. You don't need it all the time, but it's good to know you have it so you can go "Hey, I can do that, I'll jut switch on deep memory".With a 4 channel scope you can go "Hey, I can view that at the same time, I've got 4 channels!"You might not think you need 4 channels if you have always been limited to 2 channels and you had no choice.The Rigol DS1054Z, the defacto standard entry level scope, has now made 4 channels kind of an expected thing.There are countless usage scenarios. One might be where you are debugging a circuit. It's common to have one probe on the rail to make sure there is no funny business there (sometimes more than one rail), one for the signal you are inspecting, and another as a trigger signal you also want to view and not just trigger from, maybe another on the reset line looking for funny business there etc.Basically, 4 channels gives you the ability to hunt for those time correlated "funny business" problems.

author: con-f-use
author_rank: Unknown
timestamp: September 17, 2015, 12:36:26 pm
content: Back when I only had a 2chn, I would run into situations, where I need 4chn about once a month. I mostly do small micro controller stuff. For bus debuging it's really useful. I still curse Keysight, that their MSO2000 series scopes don't allow serial decoding with the logic channels, you gotta use the analogue channels and they are usually in use.

author: GNU_Ninja
author_rank: Regular Contributor
timestamp: September 17, 2015, 02:05:21 pm
content: The number of channels on a scope is similar to the number of arms required when soldering or working on stuff. Four is a minimum requirement I reckon

author: daqq
author_rank: Super Contributor
timestamp: September 17, 2015, 02:06:22 pm
content: As others have said - most of the time you do indeed need only the 2 channels, but when you need more channels you are buggered without more channels.Yeah, you can eventually measure pretty much anything with only two channels, assuming you trigger from one signal and sequentially measure the rest (and assuming this is a completely repeating set of waveforms) - but you can miss some important event, you can miss a correlation and what's more, when you change your setup you need to do the measurements all over again - essentially, instead of just changing a value of a trimpot and seeing the result immediately, you wait for another round of playing around with cables.It's like having only one multimeter - you can measure either current, or voltage, but not both.

author: Berni
author_rank: Super Contributor
timestamp: September 17, 2015, 03:30:43 pm
content: While you don't absolutely need it you will find it very very useful in digital stuff.Most of the time you will still use just 1 or 2 channels at the same time, but here and there the extra channels will be a life saver if you need to look at a SPI bus or trigger off something while keeping an eye on a few things.Also if you do digital you really want something with serial decode in it. I just love it.

author: FrankBuss
author_rank: Unknown
timestamp: September 17, 2015, 04:35:54 pm
content: At a client side I used a 4 channel scope to debug my software on some complex circuits with FPGAs etc. and often I needed all channels. But the scope didn't have digital inputs. At home I never needed more than the 2 analog channels and the 16 digital channels of my Agilent DSO, and would have been sufficient for my work at the client too. But I'm mostly a programmer and don't develop or debug analog circuits. All I need sometimes is to see the rise time, ringing or glitches of one or two signals, the rest can be digital.

author: _Wim_
author_rank: Super Contributor
timestamp: September 17, 2015, 05:57:34 pm
content: As a beginner, I do not see any good reason NOT to by the ds1000z series, unless you absolutely want to spent more. Sometimes I think Rigol is charging too less, because it makes beginners think they are not buying something "good", and are afraid they will outgrow it fast. But I think the reality is that most occasional hobbyist like myself will not easily be limited by a scope like this. This does not mean there wont be a use case were we could use some more bandwidth or some more XXX, but it means that armed with this scope and some creativity, we are able to make all of your projects work. And the money we saved buying the low cost scope, we cant spent on other goodies...

author: rt
author_rank: Regular Contributor
timestamp: September 17, 2015, 06:29:40 pm
content: Yes the MDO gives you 16 digital channels but sometimes your "digital" signals ARE NOT behaving in a nice binary way.As others have said above, sometimes the only way to diagnose misbehaving "digital" lines is looking for correlated analogue glitches, coupled AC, line ringing, slow rise/fall times, etc and for that having 4 channels is great.rt

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: September 17, 2015, 06:48:15 pm
content: My life lesson learned was it is better to have and not need then not have and need later down the road..I just got a Rigol DS1054z and I love it and it was a big up grade from my BK 1022 20mhz 2 Channel scope..Also remember if one channel every goes dead then you still have 3 channels left to use .

author: Mark
author_rank: Frequent Contributor
timestamp: September 17, 2015, 06:59:42 pm
content: I have a couple of DS1054Z's and another 2-channel scope hooked up to the same test system for a total of 10 channels, so I would definitely advise picking up a Rigol DS1054Z, it's an absolutely brilliant little scope with very useful 24M points memory depth.To compare with logic analysers, there are times when I absolutely need the 34 channels of my intronix logic port, but would like more memory depth, and there are times when I absolutely need the memory depth of my 16 channel Jiankun logic analyser but would like more channels. To have both 4 channels and an excellent memory depth in one oscilloscope is worth a lot more than the Rigol's asking price.

author: KL27x
author_rank: Super Contributor
timestamp: September 17, 2015, 08:24:42 pm
content: Unless you need the portability, I would rather have a separate DSO and a computer-interfaced logic analyzer. When working on 16 signals, it's rather nice to be able to use a keyboard to quickly label your signals and to use the mouse to scroll and set move flags. An oscilloscope already has enough buttons and wheels on it. You might need an MSO for a specific reason, I suppose.I have used more than 2 channels, once. That one problem was the reason I upgraded my scope to 4 channels. If I need an MSO, I'll buy one at that point in time. (Or maybe I'll even try to make sense of the built in LA on my Hantek "MSO," but it doesn't really seem to be an MSO as much as a separate scope and really crappy LA in the same enclosure; I bought it because it was the cheapest 4 channel scope I could find, at the time). Buying an MSO to avoid buying a separate LA is like buying a table saw with a corkscrew attachment, to build cabinets and open wine bottles.

author: rsjsouza
author_rank: Super Contributor
timestamp: September 17, 2015, 09:24:30 pm
content: I never had a 4ch scope before my current one, and I can tell how useful it is in scenarios mentioned by Dave's post: it greatly helps to keep track of areas of the circuit that are apparently unrelated to the main troubleshooting focus. Obviously that it can be done with a 2ch as well, but in a less convenient way.Before getting the oscilloscope above, I was in a similar scenario as you: torn between the more featured DS2000 but only with 2 channels, or aiming for the budget DS1000Z and its 4 channels. I ended up getting the best of both worlds with a DS4014, but only because the circumstances conspired to close the deal.

author: KL27x
author_rank: Super Contributor
timestamp: September 17, 2015, 10:44:34 pm
content: Might be worth noting that, last I checked them out, Siglent has scopes that are locked to two channels but can be software upgraded to 4 channels for another ~$200.00 if/when you need it. If the scope isn't superfluous/obsolete by then.I'm not keen to pay for the latest and greatest in DSO's. If you think your scope is a bargain today, wait 5 years. Digital changes everything, and interfaces, features, options are just going to get better and cheaper. "So I don't have to upgrade, later," is not necessarily a good reason to buy stuff, today. Upgrading later might be a bonus.

author: jolshefsky
author_rank: Regular Contributor
timestamp: September 17, 2015, 11:25:24 pm
content: Here's one way to look at it: take arbitrarily the Tektronix MDO3012 (2-channel 100 MHz Mixed-Domain). It's about US$3,600. The MDO3014 (4-channel 100MHz Mixed-Domain) is about US$4,300. If you buy the 2-channel and realize you want the four, there's no way to spend US$700 to get 2 more channels.I see two paths to buying an oscilloscope. If you have zero oscilloscopes and are strapped for cash, buy the cheapest decent 'scope you can. But if you want to invest in a tool to last several decades, buy the most feature-rich, top-brand 'scope you can.

author: nctnico
author_rank: Super Contributor
timestamp: September 17, 2015, 11:45:59 pm
content: Quote from: jolshefsky on September 17, 2015, 11:25:24 pmNO! Technology is moving forward too fast nowadays to assume today's test equipment will meet tomorrow's needs. In other words: buy equipment you need today and assume you'll upgrade it in a few years.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 18, 2015, 02:29:08 am
content: Quote from: TorqueRanger on September 17, 2015, 06:48:15 pmThat's exactly my thought on why I don't want to get the 1054Z. The 1054Z doesn't have enough bandwidth. I would like to display up to the 9th harmonic of a 25 MHz square wave with negligible attenuation, this would require a minimum bandwidth of 225 MHz. The MSO2072A (hacked to 300 MHz) has a calculated system bandwidth of 228 MHz, this would be perfect. Psychologically the 1054Z feels like a toy due to its price point and cobbled together features and functionality. If I bought it, I think in the back of my head I would always be wishing I had more scope. It would drive me crazy.I have an old Tektronix 2213A 60 MHz analog scope, couldn't I use that if I needed two more channels?

author: KL27x
author_rank: Super Contributor
timestamp: September 18, 2015, 02:51:19 am
content: Yes, that's two more channels if it has an external trigger. One more if it doesn't. Helps if they have the same timebase, when you go to put calipers on the screen to figure out your offsets.Hantek is an oddball, here. 2/4/8 rather than 1/2/5.If you don't currently have a reason for it, then maybe you don't need it. When you do, there could be a shinier scope for cheaper. A lot of the obvious improvement are going to be in software/GUI, larger screens, capacitive touch, et al.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2015, 02:56:18 am
content: Quote from: nbritton on September 18, 2015, 02:29:08 amIn some situations yes, but most of the time with modern scope you are single shop capturing and analysing the waveforms. You can't do that with an analog scope.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2015, 02:57:45 am
content: Quote from: nbritton on September 18, 2015, 02:29:08 amMost general use for scopes don't need high bandwidth. 100MHz is plenty.It's common to have a cheaper 2nd hand old high bandwidth scope (even analog) for high bandwidth signal integrity work.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:11:28 am
content: Quote from: rsjsouza on September 17, 2015, 09:24:30 pmHow did you manage that one, the DS4014 costs $2300. For $2077 you could have bought two DS2072A and one DS1054Z! I do have the money for a 4000 series, but are 4 channels really worth that much?

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:16:19 am
content: I want a cthulu channel oscilloscope. i want an infinity oscilloscope that uses transmission line effects in 3 axis

author: FrankBuss
author_rank: Unknown
timestamp: September 18, 2015, 05:46:58 am
content: Quote from: KL27x on September 17, 2015, 08:24:42 pmI develop digital electronics, but often it is really useful to see one or two analog channels together with the digital signals, for example to see the exact time when an ADC output changes. You can't do this easily with a computer-interface logic analyzer and a separate scope. For me MSOs are necessary.

author: fivefish
author_rank: Frequent Contributor
timestamp: September 18, 2015, 06:00:09 am
content: Monitoring the differential input and differential output signal (for example, balanced audio)... there goes your 4 channels.

author: TMM
author_rank: Frequent Contributor
timestamp: September 18, 2015, 06:00:30 am
content: Quote from: EEVblog on September 18, 2015, 02:57:45 amWorth noting that even if you mod the 1054z to 100MHz, running 4 channels at 250MSa/s can be a bit iffy if you are looking at 25MHz+I had a DS1052E, sold it and bought a DS1054Z. 4 channels is great and since most of the work I do is low frequency (<1MHz) the sample rate isn't an issue. The things I miss about the 1052E were alternate triggering and having a dedicated trigger input. Sometimes I'm looking at 4 channels of analog where two channels are >1MHz and two channels are <10KHz. Without alternate triggering, I'd be better off having two 2-channel scopes instead.

author: MarkF
author_rank: Super Contributor
timestamp: September 18, 2015, 06:49:27 am
content: Quote from: nbritton on September 18, 2015, 02:29:08 amSounds to me like you've already made up your mind. Get the MSO4034. You won't be satisfied with anything less.

author: ebastler
author_rank: Super Contributor
timestamp: September 18, 2015, 06:59:53 am
content: Quote from: nbritton on September 18, 2015, 02:29:08 amThat's a surprisingly specific requirement. I'm curious what application is defining that specific need? Or is it "reverse engineered" from the spec of the MSO2072A?

author: nbritton
author_rank: Frequent Contributor
timestamp: September 18, 2015, 07:51:01 am
content: Quote from: ebastler on September 18, 2015, 06:59:53 amI inferred it by studying the Fourier series of a square wave, the summation of the first five odd harmonics (fundamental, 3rd, 5th, 7th, and 9th) is the first waveform that accurately approximates a true square wave. I settled on 25 MHz because I'm going to be working with computer equipment and it's what I can afford, it also happens to be the fastest square wave that the Siglent SDG1025 can drive.

author: Berni
author_rank: Super Contributor
timestamp: September 18, 2015, 09:41:30 am
content: In practice i use more of a rule of thumb.For checking signal integrity like overshoot you tend to need a scope with x10 the bandwidth of your signal. While for just looking at what the signal is doing about 3x to 5x is enough.A 25MHz square wave will look a bit better on the actual scope because the bandwidth will slowly roll off after its spec, not just suddenly drop off a cliff. So you do get some harmonic content past the bandwidth, just that its attenuated more and more as you go out, making the signals edges round off rather than show this ringing on the top.Now this does not mean oh i have buses going at 100MHz so i absolutely must buy a 1GHz scope. I seen some pretty horrible digital signals fed in to some of my digital circuits. Yet the thing still kept on working fine. So if the signal looks clean on a low bandwith scope in most cases it is good enough. And if there is weird stuff happening you usually just need to fix the clock signal (Twist a wire with ground for it, use a shielded wire, add some termination resistors or pF caps to fine tune the ring away etc). Where you want to have a really high bandwidth scope is when you are making a product and you want to make sure all your signaling is well within the integrity requirements of the chips. So that variation in chip quality or temperature and other conditions for sure wont cause it to fail due to crap signal integrity.As people said buy what you need now and then if you need the bandwidth buy an extra old scope off ebay. A 500MHz scope is not hard to get cheep on there if you don't mind it being old. (I recently bought for 6 grand a 4GHz Agilent scope that is still being manufactured)

author: Galenbo
author_rank: Super Contributor
timestamp: September 18, 2015, 10:00:27 am
content: Quote from: nbritton on September 16, 2015, 11:47:51 pmI think most things are "possible", but there's also the "easy" and comfortable aspect of it.For signal conditioning, isolation and converting, I like it that I can look at 4 steps of the process at 1 time.Changing 1 component value has an effect in the whole line, and you don't know immediately where a new problem can pop up.The probes can stay where they are.

author: Galenbo
author_rank: Super Contributor
timestamp: September 18, 2015, 10:07:19 am
content: Quote from: nbritton on September 18, 2015, 03:11:28 amAre 4 channels AND big bandwidth needed at the same time?

author: tautech
author_rank: Super Contributor
timestamp: September 18, 2015, 10:10:47 am
content: Quote from: KL27x on September 17, 2015, 10:44:34 pmNot that I'm aware of, link or model please.

author: retrolefty
author_rank: Super Contributor
timestamp: September 18, 2015, 10:20:47 am
content: Well i'm an old fart that grew up with just two channels + external trigger scopes. Good enough for me so good enough for you kids. Heck they sent men to the moon when 2 channel scopes ruled the world.Seriously if 4 channels is desirable why not 6 channels, or 8? I'm sure there is a use case for someone out there. I would think that each added channel requires it's own ADC? if so each added channel carries a cost that should be factored in such a purchase decision?So to the OP I would advise him to get what he can best afford and if that lands him in two channel land then don't worry about it and just learn to master his new tool. One thing I know about scopes is that the person at the other end of the scope probe tends to be the limiting factor as far as effectiveness and usefulness of a scope no matter the number of channels and features.

author: Fungus
author_rank: Super Contributor
timestamp: September 18, 2015, 10:23:35 am
content: Yes!(And if you're even asking this you're probaby going to be told to buy that DS1054Z anyway, which is a 4-channel 'scope, so)

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2015, 10:30:57 am
content: Quote from: nbritton on September 18, 2015, 07:51:01 amBut do you really need to measure theactualsignal fidelity to such detail? Most people don't.Do you know that you can't use the normal probe ground lead to do that?, you need proper high frequency probing techniques.For looking at 25MHz square waves, 100MHz bandwidth in practice is usually fine because scope bandwidth don't drop off like a brick wall.

author: Howardlong
author_rank: Super Contributor
timestamp: September 18, 2015, 11:32:00 am
content: If you are doing digital and have an MSO then 2+16ch will do.Almost all of my work is mixed signal embedded. If I were offered the choice of 2+16 or 4+0, all other things being equal, it's a really tough choice. Probably I'd go with 2+16. Certainly if your intention is parallel busses as you've mentioned in another thread, then definitely, 2+16 over 4+0.For a while even quite recently I used 2+16 in the lab on a daily basis even though I had 4+16 available, the 2+16 was just a much more easy to use scope (the 2+16 is an Agilent 54642D Megazoom 500MHz/2Gsa/s, the 4+16 is an Agilent 54831D Infiniium 600MHz/4Gsa/s Windows based scope with a boot time to match). I had the 54642D trigger permanently hooked up to a 54622D, so I could get a couple more analogue channels if necessary on the odd occasion. The use case for that was usually when doing switch mode power supplies, although even four channels is often marginal when doing SMPS!I too was brought up on 2ch CROs, when I could even get my hand on a scope at all that is, and you can do an awful lot with that, and usually you can do all that you need, it's just much more convenient with more channels, there's less manual pen+paper work involved.It sounds like you may be having a case of what I call "analysis paralysis", and I don't mean that in a negative way, I suffer from this affliction regularly: just keep in mind that any scope is better than no scope at all!