Information overload. I'm confused. Do I really need four channels?

[JohnG]

FWIW, I do a fair amount of power supply design and debugging, and find that I frequently use 3 or 4 channels, and there are times when I wish I had more. When you have to start chasing down gate drive delays, startup, issues, etc., it is almost essential. If you are chasing failures, you can capture more stuff and look at it later, so yo don't have to keep the DUT running any longer than necessary.

Also, if you are working on high density power electronics, you may find yourself probing DFN gate drives right next to a few hundred voltages and a low impedance bus. I don't know about you, but I don't like moving probes around when a false move can fry the circuit, the probe, and you. Even a slip at the signal level some distance away can still result in exploding power parts.

John

[rstofer]

As mentioned, 4 channels is only rarely required.  More often than not, a single channel is sufficient.  But the thing is, when 4 channels would be a help, a 2 channel scope is not.  I bought the DS1054Z specifically for the 4 channels and the decoding.  If I wanted a higher frequency 2 channel scope, well, I already had one.

"The screen is too small!".  Well, yes, it's kind of small but it's twice the area of my Tek 485 and nobody ever complained about those scopes!  When I'm displaying 4 channels, they will be digital traces.  How tall do they need to be just to show a logic level?  Then I add decoding and the trace count increases but, somehow, it all works out!

Yes, I would like to buy a Keysight <something> with a huge screen, oodles of channels and bandwidth but I really can't afford it.  So, I bought what is most likely to cover what I plan to do.

[tggzzz]

As mentioned, 4 channels is only rarely required.  More often than not, a single channel is sufficient.  But the thing is, when 4 channels would be a help, a 2 channel scope is not. 

... and when you need 5 channels, e.g. for logic timing, then 4 is insufficient!

"The screen is too small!".  Well, yes, it's kind of small but it's twice the area of my Tek 485 and nobody ever complained about those scopes! 

But, delightful as it is, a 485's screen is very cramped with dual channels plus ALT timebase

When I'm displaying 4 channels, they will be digital traces.  How tall do they need to be just to show a logic level?  Then I add decoding and the trace count increases but, somehow, it all works out!

Logic analysers are designed for just such purposes, and aren't limited to only 4 channels

[saturation]

A trick is feed the trigger out of the main DSO to the slave DSO ext trigger in.   Final stability varies with many factors, mainly the sweep speed, the quality of the trigger out waveforms and any adjustments possible on both DSO to compensate for cable delays and skewing in multiple daisy chained DSO but in general the sync can be adequate.  You can also use multiple DSO networked together and software but the prior method is fast, quick and easy for < 100 MHz, you could do better with better gear.  I do this on occassion on the GDS1054B as master for the Rigol 1052e slave to have a 6 channel view, the Rigol can be jittery but I work around it.

FWIW, I do a fair amount of power supply design and debugging, and find that I frequently use 3 or 4 channels, and there are times when I wish I had more.

[alsetalokin4017]

 

[Artikbot]

Oooo!

That looks so pretty. Me likey.

And not something I have actually ever been able to accomplish with the old relics - always had to repeat measurements a few times, take pictures with the camera mounted on the tripod (or record the screen!!) and then go from there.

Needless to say results were... let's say interesting.

[nctnico]

When I'm displaying 4 channels, they will be digital traces.  How tall do they need to be just to show a logic level?  Then I add decoding and the trace count increases but, somehow, it all works out!

Logic analysers are designed for just such purposes, and aren't limited to only 4 channels

But then you'll need to reconnect channels which is tedious to do and you miss the analog information which may be crucial for the problem you try to tackle (*). On my Tektronix logic analyser I have 4 analog outputs which I can switch to any input. In some cases I just use the logic analyser as an analog mux to look at the various digital signals on an oscilloscope.

(*) A couple of years ago someone had to integrate a bit of hardware I designed into a bigger system. That person spend a couple of weeks on trying to get it to work but gave up. I went over there and the first thing I did was use the analog channels instead of the digital channels of his MSO to look at the signals. The problem became appearant in less than 10 minutes and half an hour later we had it working.

[tggzzz]

When I'm displaying 4 channels, they will be digital traces.  How tall do they need to be just to show a logic level?  Then I add decoding and the trace count increases but, somehow, it all works out!

Logic analysers are designed for just such purposes, and aren't limited to only 4 channels

But then you'll need to reconnect channels which is tedious to do and you miss the analog information which may be crucial for the problem you try to tackle (*). On my Tektronix logic analyser I have 4 analog outputs which I can switch to any input. In some cases I just use the logic analyser as an analog mux to look at the various digital signals on an oscilloscope.

(*) A couple of years ago someone had to integrate a bit of hardware I designed into a bigger system. That person spend a couple of weeks on trying to get it to work but gave up. I went over there and the first thing I did was use the analog channels instead of the digital channels of his MSO to look at the signals. The problem became appearant in less than 10 minutes and half an hour later we had it working.

No surprises there!

As I've written many times before, first use a scope to ensure signal integrity. Once you have good (analogue) signals that will be correctly  interpreted as digital signals, flip to debugging in the digital domain. Use the right tool for each part of the job.

But how many analogue inputs do you need simultaneously to ensure signal integrity? In most cases only two, to measure setup and hold times.

[nctnico]

Why bother reconnecting if a little bit more buys you a tool which can do both? When the digital suddenly starts to misbehave you have to go back to look at the analog signals again. All in all switching between a logic analyser and an oscilloscope (reconnecting the probes) is just a nuisance you can avoid by having more channels. I have a four channels Agilent DSO7104A with the MSO option but in nearly two years I have not used the digitals channels at all.

[tggzzz]

Why bother reconnecting if a little bit more buys you a tool which can do both? When the digital suddenly starts to misbehave you have to go back to look at the analog signals again. All in all switching between a logic analyser and an oscilloscope (reconnecting the probes) is just a nuisance you can avoid by having more channels. I have a four channels Agilent DSO7104A with the MSO option but in nearly two years I have not used the digitals channels at all.

That is a rather contrived use-case; it feels you are finding a problem for your solution.

It is, of course, entirely possible to have some digital lines and some analogue problems on other lines. In that case, use a logic analyser on the digital lines and a scope on the analogue lines.

[Keysight DanielBogdanoff]

I'd agree. We see people very happy with our two channel scopes, but those are people who generally only need two channels.

Four channels is nice, but it's certainly not always a need (especially in a value vs. $ budget dilemma).

Just my 2 cents (not 4 cents).

[nctnico]

Why bother reconnecting if a little bit more buys you a tool which can do both? When the digital suddenly starts to misbehave you have to go back to look at the analog signals again. All in all switching between a logic analyser and an oscilloscope (reconnecting the probes) is just a nuisance you can avoid by having more channels. I have a four channels Agilent DSO7104A with the MSO option but in nearly two years I have not used the digitals channels at all.

That is a rather contrived use-case; it feels you are finding a problem for your solution.

It is, of course, entirely possible to have some digital lines and some analogue problems on other lines. In that case, use a logic analyser on the digital lines and a scope on the analogue lines.

Why insist on jumping through hoops where there is an easy way offered by a 4 channels oscilloscope? If using a 2 channel oscilloscope was so easy for every situation then why would manufacturers even bother to make 4 channel oscilloscopes? AFAIK Yokogawa still makes 8 channel models!

[tggzzz]

Why bother reconnecting if a little bit more buys you a tool which can do both? When the digital suddenly starts to misbehave you have to go back to look at the analog signals again. All in all switching between a logic analyser and an oscilloscope (reconnecting the probes) is just a nuisance you can avoid by having more channels. I have a four channels Agilent DSO7104A with the MSO option but in nearly two years I have not used the digitals channels at all.

That is a rather contrived use-case; it feels you are finding a problem for your solution.

It is, of course, entirely possible to have some digital lines and some analogue problems on other lines. In that case, use a logic analyser on the digital lines and a scope on the analogue lines.

Why insist on jumping through hoops where there is an easy way offered by a 4 channels oscilloscope? If using a 2 channel oscilloscope was so easy for every situation then why would manufacturers even bother to make 4 channel oscilloscopes? AFAIK Yokogawa still makes 8 channel models!

Those are strawman points.

Look at the topic, viz: "Do I really need four channels?". That's "need", not "could used if available"!

[JohnG]

Look at the topic, viz: "Do I really need four channels?". That's "need", not "could used if available"!
[/quote]

The OP also indicates he is planning on working on motor drives and power supplies, both high and low power. I have worked in this area for a number of years. You have high speed digital controllers, isolators both analog and digital, little bootstrap converters to supply floating drivers, often multiple analog outputs, etc. It's a mix of both high power and sensitive analog and digital stuff, with both low bandwidth and high bandwidth requirements. My read is that he is looking to gain something greater than beginner expertise in this area. If that is true, then 4 channels is a need. I have 4 channels and still find myself switching probes.

If all you are doing is experimenting with a single-active-switch converters or similar with old analog controller, you could get by with 2 channels, but even there, 4 channels is better than 2 if you really want to gain a deeper understanding of what is going on.

John

[rstofer]

As mentioned, 4 channels is only rarely required.  More often than not, a single channel is sufficient.  But the thing is, when 4 channels would be a help, a 2 channel scope is not. 

... and when you need 5 channels, e.g. for logic timing, then 4 is insufficient!

When I'm displaying 4 channels, they will be digital traces.  How tall do they need to be just to show a logic level?  Then I add decoding and the trace count increases but, somehow, it all works out!

Logic analysers are designed for just such purposes, and aren't limited to only 4 channels

Absolutely but the scope is right in front of me and the logic analyzer (32 channels/100 MHz, 16 channels/200 MHz) needs to be fetched and connected to a PC.  All in all, a bother since I usually want to watch a simple SPI transaction.  And I'd like to do this simple thing without a lot of fuss!  If I am watching come incarnation of 'current state' in an FSM, yes, I will use a logic analyzer.  The problem these days is that, on many development boards, there simply aren't enough IO pins.  Thankfully, Xilinx has solved that problem with their Integrated Logic Analyzer.  I'm not fully up to speed on the IP but, so far, it looks very capable.

This is what I'm using:
https://www.sump.org/projects/analyzer/

One big advantage of the logic analyzer is the triggering.  On the sump.org unit, triggering is pretty slick.  Multiple levels, etc.

I've gotten along with 2 channels for decades.  I decided one day that I could afford a simple 4 channel scope, warts and all.  It's just a hobby!
Do I NEED 4 channels?  No!  But I want them, I can afford them and now I have them.

[rstofer]

Real life problem (in my corner of the sandbox):  You have modeled an automotive suspension system (front) and you want to display:  Forcing function (from arbitrary waveform generator), suspension displacement, velocity and acceleration.  No, at the moment, I don't have enough analog computer to be able to model this but I'm working on that.  I'm having so much fun with analog computing that I will probably build a more capable unit early next year.

I need to have it built and debugged before my grandson gets to Differential Equations!  I really wish I had had that capability when I took DEs.  Anybody remember the Predator-Prey problem?  According to the textbook, the cross-coupled equations are probably unsolvable.  But the solutions can easily be displayed with an analog computer.

Besides SPI decoding, this type of thing is the primary reason I wanted 4 channels.  I was considering building a 4 channel multiplexer but it was easier to just buy the scope.

Here is a very sophisticated multiplexer:
http://www.vaxman.de/projects/scope_multiplexer/scope_multiplexer.html

Note that is has 4 PAIRS of X-Y inputs.

[JanJansen]

If you take a look at better brands, the 4 channels cost almost double the 2 channel cost.
Its not about channels, its about you want cheap or cheaper, else you would get the 2 channel without thinking.

[rstofer]

If you take a look at better brands, the 4 channels cost almost double the 2 channel cost.
Its not about channels, its about you want cheap or cheaper, else you would get the 2 channel without thinking.

That's exactly right! 

I already had the Tek 485 scope to handle 350 MHz dual channel applications.
What I wanted was a capable, 4 channel scope for hobby purposes.  I'm not in the business, I can't write it off my taxes, it's just a hobby.
But it's only one hobby of several so there is a limit to how much I can spend on it.  Fixed income and all.

For my hobby purposes, the DS1054Z meets all my needs.  Unlocked, it is the best scope on the market less than $1200 or so.  Why would I spend 3 times as much to get an equivalent scope?  It's just a hobby!

As to a signal generator, I think I'll eventually buy either the Siglent or the Rigol.  At the moment, I don't need an AWG because my Digilent Analog Discovery is quite capable in the lower frequency (20 MHz) end of the game.

But the question was "Do I really need four channels?" and the answer is no.  Most of the time...

[tggzzz]

... snipping stuff I agree with...

But the question was "Do I really need four channels?" and the answer is no.  Most of the time...

The older I get, the more I'm sure my younger instincts are correct.

The answer to "do I need X?" is always "no".

The response to "I need X in order to Y", is always "is Y the really important objective?", and (if the answer is affirmative) followed by "I have a Z1 and a Z2, can I use them to achieve Y?", and (if the answer is negative) that's followed by "I know the only way of achieving Y is with an X".

[Artikbot]

I feel it is my duty to report back on this - the scope has been delivered! 

It unlocked all features first try (that's how I am - sorry!). I'll give it a try in the coming days with some gear that needs to be looked at (power LED lamps and some other stuff).

Thanks to everyone who contributed!

[Howardlong]

Be sure to let us know how you get on, good, bad or ugly.

[tggzzz]

Be sure to let us know how you get on, good, bad or ugly.

Please do.

Often the most interesting information will be surprises, both pleasant and unpleasant.