Scope , 2 or 4 channels , can you explain the pros and cons of each one ?  - Page 1
Forum section: electronics / testgear

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 04, 2013, 12:04:43 am
content: HeyI'd liketo hear your opinion based on your experience .Let's assume that i don't know anything about scopes , might you explain me the real need for 4 channels on the same screen ? ,Don't know if the title is good fit to the subject , feel free to tell me what shall I include in the title .Besides it's nice to see how waveforms relate to each other . Triangle wave into square and then into PWM .. okay that's nice to see on the same screen ... But when it become essential for real ?Sorry for those mistakes ... I am writing via my phone hence no translation applies .. I might fix that tomorrow .. good night for now

author: digsys
author_rank: Unknown
timestamp: June 04, 2013, 12:36:44 am
content: That's not someoneelsecan answer, only you and what work you intend to use the DSO for. IF you need more than 2 channels,trust me, there's nothing else you can do as a compromise. Even using 2X 2ch scopes has serious limitations.Hardware / software() developers / fault-finding and all sorts of people NEED 4 channels, even if it just for simultaneous expanded channels.The question is justtoobroad. If you need it, you'll know.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: June 04, 2013, 12:49:28 am
content: The biggest thing I've used a 4 channel for is in 3 phase power. That's something that most hobbyists aren't going to be dealing with. There are many other uses, though. It really depends on what you do with it.

author: w2aew
author_rank: Super Contributor
timestamp: June 04, 2013, 01:24:04 am
content: Quote from: eevblogfan on June 04, 2013, 12:04:43 amIn my opinion, there really aren't any downsides to having more channels, other than it will cost you more in general. Looking at the choreography of many signals, or being able to observe the changes a signal goes through at various stages in a circuit, can all be very helpful depending on what you are working on. Mixed Signal scopes can add multiple digital signals to the mix.Many of the tutorial videos on my youtube channel show more than 2 channels being used (the PLL tutorial is one example where four analog channels are used, and the op amp basics uses three channels if I recall correctly).If you can afford to get more than two channels, then there is no downside in my mind.

author: Harvs
author_rank: Super Contributor
timestamp: June 04, 2013, 03:34:20 am
content: Cost. If there was a 4-channel scope with similar capabilities to the DS2000 within a similar price range (i.e. maybe add 50%) then I would have bought it in a flash.The closest rigol is >3x the price to get the extra two channels.It's the same deal with MSOs, add what appears to be only 20-30% more hardware and the cost triples or more.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 04, 2013, 09:11:13 am
content: heythe distributor who sold me the DSOX2002 for 820$ is now offering me to up-grade into the 30XX series , I don't know yet what is the price thought , and it begins from 100Mhz , witch is okay for me at this point in time , though 4 channels might come into play soon , hence I wanted you to shear with me your experience with that 4 channel need . might you simply describe the setup and what did you do with 3 or 4 of the channels ?thank you in advance

author: EEVblog
author_rank: Unknown
timestamp: June 04, 2013, 09:51:35 am
content: Sometimes 4 channels isn't enough! I've used all 4 channels quite a few times in my videos. Sometimes it's essential, sometimes not, depends entirely what you are working on.Let's put it this way, 2 channels isbarely enoughto see one signal in relation to another (a basic oscilloscope use), it leaves you no scope for anything more.

author: jpb
author_rank: Super Contributor
timestamp: June 04, 2013, 09:57:21 am
content: I have a 4 channel scope but I've only had it since January and as I only get to do electronics in my spare time I've not yet reached the stage that I have to use all 4 channels, but some of the reasons I went for it (over 2 channels) where:1.) I felt the down side of finding 2 channels not enough outweighed the risk of spending more and not using the extra channels much.2.) If I wanted to look at say SPI signals I'd need more than 4 channels (I know you can use digital channels but if you're interested in pulse shape you need analogue).3.) 4 channels allow you to look at say Voltage and Current on both input and output of a circuit.4.) 4 channels allows you to use two channels at maximum sample rate (i.e. I can use two channels at 2GS/s whilst with a 2 channel scope I'd be down to 1GS/s).5.) Generally, if you want to keep track of an input signal, an output signal and trace some internal circuit signal you'll need more than 2 channels.Before I bought my scope I generally trawled the web for advice (as you are doing) and though most people were happy with 2 channels a significant number said they needed 4 channels and most said they would like 4 channels. Here is one guys advice on buying a scope for embedded systems which I found quite useful even though I ignored much of it!To quote from it :"I always try to get a mixed-signal scope with 4 analog channels and 16 digital channels. Two analog channels is not enough -- I often have to view 3 or 4 channels at once. (maybe once every few years I wish there were a 5-channel scope!)"http://www.embeddedrelated.com/showarticle/117.php?articleid=117

author: jpb
author_rank: Super Contributor
timestamp: June 04, 2013, 09:59:41 am
content: Quote from: EEVblog on June 04, 2013, 09:51:35 amWas that a deliberate pun?

author: c4757p
author_rank: Super Contributor
timestamp: June 04, 2013, 10:31:41 am
content: Quote from: jpb on June 04, 2013, 09:59:41 amI thought it was just literal: no more oscilloscope.

author: saturation
author_rank: Super Contributor
timestamp: June 04, 2013, 01:19:38 pm
content: The basics of 2 ch scopes is to see input and output waveforms simultaneously, real time. On complex circuits with multiple stages or multiple analog i/o, you can examine the preprocess stages in real time, enroute to the output. The more channels you can see simultaneously, the faster you can evaluate it without having to reset your probes. 4 channel scopes would also better with bigger displays, otherwise the waveforms can get pretty cramped.

author: ToBeFrank
author_rank: Regular Contributor
timestamp: June 05, 2013, 12:38:42 am
content: From a software perspective, I say 4 channels is a must. For example, I needed to decode a J1850 VPW signal in software. I used one channel to display the incoming signal, two channels to show when I was in the separate interrupts, and the last channel for debugging when I was in various sections of my code. This would have been much more difficult with only two channels.

author: Dave
author_rank: Super Contributor
timestamp: June 05, 2013, 12:51:31 am
content: I can really think of only one advantage in having a 2-channel oscilloscope, instead of 4.When you are limited by something (only two channels), you are challenged to think of a way to work around that limitation. In a way, it provokes creativity. But still, this is not a good enough reason to go for a 2-channel scope, if you have the money to buy a 4-channel one.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 05, 2013, 01:18:25 am
content: HeyDave --- let's say I got 10k$..shall I buy 200Mhz 2 channel scope . and spend th :-//e rest on good bench LCR and other gear . or shall I spend the 10K$ on single 4 CH scope ( don't know the BW you can buy with 10K$ ...

author: EEVblog
author_rank: Unknown
timestamp: June 05, 2013, 01:26:48 am
content: Quote from: eevblogfan on June 05, 2013, 01:18:25 amYou can get a 4CH scope for only a few $K, no need to spend $10K, that would be silly.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 05, 2013, 08:59:28 am
content: Hey DaveI know what the prices are ,the destrebitor who sold me that DSOX2002 for 820$ is now offering me to trade the scope and getting DSOX30XX with 40% discountthe question is - is it worth it to buy 4CH 100Mhz scope or 2CH 200Mhz scope ?thank you in advance !

author: Dave
author_rank: Super Contributor
timestamp: June 05, 2013, 10:36:46 am
content: Quote from: eevblogfan on June 05, 2013, 01:18:25 amWell, that really depends on what you need in your lab. If you don't have many other tools, you should obviously go for the cheaper scope and use the rest of the money on other equipment.When I said "if you have the money", I meant if you have the moneyfor a scope. A part of your savings you are actually willing to spend on that scope. You are obviously not going to blow your whole bank account on a single scope. At least I wouldn't.Quote from: eevblogfan on June 05, 2013, 08:59:28 amI'd go for the 4CH 100MHz, but that's just my personal preference. So far, I have never needed to analyze waveforms above 40-50MHz, for things above that, I only needed to measure the frequency itself, and I have a dedicated microwave frequency counter for that.Pick the tools according to your needs.

author: nctnico
author_rank: Super Contributor
timestamp: June 05, 2013, 11:31:15 am
content: Quote from: eevblogfan on June 05, 2013, 01:18:25 amI'd always choose the 4 channel scope. There are many second hand units for sale well within such a budget like the Tektronix TDS3000B series.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 05, 2013, 05:39:42 pm
content: heythe sampeling rate has been mentioned and I femilliar with that case thank to Dave's videos , at this point in time I rather buy Ersa soldering station , and spend the rest on 3 projects I plan on ,PS : the man told me 2.5$ plus my current scope ( the DSOX2002 ) for the DSOX3014so within 3 month of work I can get that scope ( I firstly pay all of my salary , then I have 3 monthes to pay the rest )If you were me , you currently don't need 4 CH scope but thinking about the future , will you spend 2~3 monthes for paying only that scope ?thank you in advance !

author: dfmischler
author_rank: Frequent Contributor
timestamp: June 05, 2013, 06:49:18 pm
content: Quote from: eevblogfan on June 05, 2013, 05:39:42 pmNo. I would like a fast 4 channel scope, but I will not buy one until I need it.

author: nctnico
author_rank: Super Contributor
timestamp: June 05, 2013, 07:23:44 pm
content: Quote from: mojo-chan on June 05, 2013, 05:28:35 pmAFAIK every DSO has 4 A/D converters. Otherwise its impossible to capture an event in single shot mode. The reason samplerates are reduced is due to limited memory bandwidths. Oscilloscopes (and logic analysers) often use regular DRAM to store the information

author: Pinkus
author_rank: Frequent Contributor
timestamp: June 05, 2013, 10:34:31 pm
content: I would tend to a 2 channel scope and a logic analyzer, given that you are on a budget.What I am reading here, most people using more than 2 channels for logic signals.It would be much much easier with a logic analyzer instead.E.g. the Logicport fromwww.Intronix.comoffers 32 channels (or 36, can't remember now) including free interpreters for SPI, I2C, CAN, RS232 etc. for just 389 US$. And the software which comes with it is pretty well done and offers tons of possibilities no scope will ever be able to offer.Instead 2 more channels you better get the analyzer and save another few hundred bucks you better spent on you wife or girlfriend (I am sure she will not argue).Peter

author: codeboy2k
author_rank: Super Contributor
timestamp: June 05, 2013, 11:07:28 pm
content: Quote from: ToBeFrank on June 05, 2013, 12:38:42 am4 channels definitely does help with this, but sometimes even that is not enough, and I need all 4 channels for viewing waveforms *and* I want to know when I am in an interrupt or how long I spent there...So, in the past I have used a frequency counter in single channel pulse width mode, or dual channel A-B mode, to count the time spent inside an interrupt; this can free up those needed channels for viewing real waveforms.In a pinch you can also whip up an edge triggered A-B pulse width counter with a few discretes on a breadboard, or another micro even.The point: for the OP.. if you are into software development, then get a basic frequency counter too, one with pulse measurement abilities. It can help.

author: Paul Price
author_rank: Super Contributor
timestamp: June 05, 2013, 11:30:15 pm
content: The real advantage of a 4-chan scope is that if you zap three of the Vertical Chans, you still got one left.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 06, 2013, 09:33:35 am
content: heythe seller offered me the following :I give him my scope (DSOX2002 ) and he refound that for 1.6K$I then have 3 month to pay 2575$and the DSOX2002 is staying with me untill I get my new DSOX3014is that worth for me >?he said that he can offer that only within that week hence I really need your answear ASAPthank you in dvcnce !

author: digsys
author_rank: Unknown
timestamp: June 06, 2013, 03:08:17 pm
content: It's a good deal, and you won't end up paying more than RRP, ie not losing $ on the deal, but itISa lot more $The question still remains - doYOUthink that you'll really need it !!!??? Never mind what everyone else thinks.You can buy OTHER really useful stuff with that kind of "upgrade" $

author: nctnico
author_rank: Super Contributor
timestamp: June 06, 2013, 03:42:14 pm
content: I agree. If there is money in my pocket then a new oscilloscope looks very appealing but there are so many other things one could buy. And in my case it has to pay for itself somewhere in the future. Maybe its better to invest in an instrument you can use to learn something new or improve your skills. I bought a spectrum analyser to be able to build and test RF circuits.

author: free_electron
author_rank: Super Contributor
timestamp: June 06, 2013, 03:47:20 pm
content: Quote from: nctnico on June 05, 2013, 07:23:44 pmnow, yes. But Look at the TDS500 and same era scopes : 2 a/d shared across 4 channels.Scopes typically do not use SDRAm but fast SRAM or self refreshing DRAM . they can't deal with the refresh cycle of normal DRAM. the incoming data does not wait because the dram needs to refresh .... Super fast scopes use a mixed architecture. the prime buffer is on board sram ( on board the a/d) this is a fifo but with a wider backend than the front end. meaning the adc spits in 8 samples of 8 bit each while the back end spits out 64 bits in parallel at 1/8 the speed of the a/d . From this this bus they go into another controller that streams this into SDRAM and can deal with the refresh. the ultrafast machines may have an intermediate buffer that widens the bus even more so they can deal with the refresh cycles.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 06, 2013, 05:42:53 pm
content: heythe scope will pay itselfthe questions are :is that price okay or shall I suspect it's wrong ?with 2,575$ I can buy too much things , is that right to play now ? or shall I wait one month and see what I'll need later ?

author: nctnico
author_rank: Super Contributor
timestamp: June 06, 2013, 07:11:55 pm
content: Quote from: free_electron on June 06, 2013, 03:47:20 pmWell, they probably use a short SRAM buffer and put the refreshes in between. The beauty of streaming data at a fixed rated is that you can plan the timing from A to Z. A lot of Tektronix TDS500/600/700 scopes use DRAM and so do their TLA700 series logic analyser modules. BTW when looking at the diagrams of the TDS500 series scopes I see 4 A/D converters. One for each channel.