Author Topic: Buying a 2CH vs 4CH Scope  (Read 1253 times)

0 Members and 1 Guest are viewing this topic.

Offline Old Printer

  • Frequent Contributor
  • **
  • Posts: 514
  • Country: us
Buying a 2CH vs 4CH Scope
« on: March 28, 2019, 08:54:14 pm »
For the past couple years I have been following many of the "What scope should I buy" threads as I am looking for my first digital bench scope. I have a couple old analog TEK's and a couple Analog Discovery's to hold me until I finally pull the trigger. Most of the threads are consumed with the "Rigol vs Siglent vs ???" subject, but the "how many channels do I need" question shows up a lot, but dealt with only briefly. The general consensus leans towards the more the better, or are you going to look at digital signals?  Many beginners on a budget opt for 2 in the end because they can't see a reason for 4. I always cringe a bit, but keep my mouth shut because it's usually a done deal by then and I have been broke too. Anyway, over in the Repair forum member Sparky is trouble shooting an old HP 6227B PS (2 CH Tracking) link below. He is tracking down an oscillation and has the "need" to look at the signal at three different test points, and points out how nice it is to be able to look at them simultaneously on one screen. I am not saying this was a make or break for the repair, but it was an analog use for more than 2 channels. I am sure there are many more, if you know of one please add it here to help future scope buyers decide.

Maybe this thread will be a place to discuss and illustrate this topic, and keep it from being buried in the war of Chinese scope maker threads :) 

https://www.eevblog.com/forum/repair/hp-6227b-dual-dc-power-supply-ripple-in-master-channel/msg1658462/#msg1658462
 

Offline 0culus

  • Super Contributor
  • ***
  • Posts: 1492
  • Country: us
  • Electronics, RF, and TEA Hobbyist
Re: Buying a 2CH vs 4CH Scope
« Reply #1 on: March 28, 2019, 09:45:29 pm »
Having 4 channels available is almost a must IMO. I used all 4 on my 2465B when I was troubleshooting a problem in a 3325B function generator a while back. Ch3 and Ch4 are limited to 0.5 and 1 volt/div settings on this scope, but they are still handy to have. I'd rather have it and seldom need it than end up in a situation where I need it and don't have it. For multitudes of digital signals, I have a Tek TLA 715 logic analyzer.
 

Online nctnico

  • Super Contributor
  • ***
  • Posts: 17221
  • Country: nl
    • NCT Developments
Re: Buying a 2CH vs 4CH Scope
« Reply #2 on: March 28, 2019, 09:52:17 pm »
IMHO it depends on what you are working on. For most repair work 2 channels should do the job. When designing electronic circuits 4 channels (or even more) is very convenient. I can probably put an 8 channel scope to good use...
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online GregDunn

  • Frequent Contributor
  • **
  • Posts: 697
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #3 on: March 28, 2019, 09:52:39 pm »
Generally if I need more than one input, 4 is barely enough.  I kept my old Tek 922 just so I'd have spare inputs available for those eventualities.

Any time I'm troubleshooting an analog amp or a piece of test equipment, I need to look at the input and output for the section I'm working on, plus at least one more channel to follow the signal in between, and possibly control or feedback signals.  At work, doing computer stuff, we frequently ran out of channels looking at control signals and I/O; you can't use a logic analyzer to tell you if a signal has ringing or slow rise time.
 

Online TK

  • Super Contributor
  • ***
  • Posts: 1069
  • Country: us
  • I am a Systems Analyst who plays with Electronics
Re: Buying a 2CH vs 4CH Scope
« Reply #4 on: March 28, 2019, 10:20:57 pm »
This is my experience... my projects are 99% digital (MCU):

1 Channel: 60%
2 Channels: 35%
3-4 Channels: 5%

It all depends how important your 5% is.  I used it mostly to do timing analysis between sensors and the output from the MCU based on some computation (performance tuning, minimum timing constraints, interrupt analysis, etc).

I recommend buying the 4-channel scope, because you will have those 5% moments when you will regret not having the extra channels.
 

Offline AG6QR

  • Frequent Contributor
  • **
  • Posts: 779
  • Country: us
    • AG6QR Blog
Re: Buying a 2CH vs 4CH Scope
« Reply #5 on: March 28, 2019, 10:22:05 pm »
I have used 2-channel and 4-channel scopes, and I can't recall a time when the extra channels made the difference between possible and impossible.  But I can recall many times they made the difference between easy and hard.

One example:  I was using a ham radio transceiver with an external amplifier, transmitting Morse code.  The output was changing in amplitude suddenly. (to reduce bandwidth, good Morse code transmitters avoid instantaneous on/off transitions, taking a few milliseconds to ramp the amplitude up or down.)

To diagnose the problem, I had to look at the RF input to the amplifier, the RF output, and the line between the transceiver and amp which tells the amp when to switch between transmit and receive mode.

At the time, I only had a 2-channel scope.  A 4-channel unit would have cut the diagnosis time to a fraction of what I needed with that 2-channel, because 2 channels forced me to go back and forth several times between the various signals to see the relationships.

It turns out there was a firmware issue with the amplifier, where it would switch on amplification late, but only if it had recently been switched off.  A string of rapid-fire Morse dits would attempt to toggle the amp on and off too fast.

I emailed the amp designer a description of the problem, with screen captures from the scope, and less than 24 hours later, he sent me updated firmware that fixed the problem!

Details here:
https://ag6qr.net/Radio/HR50Clicks/
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 8721
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #6 on: March 29, 2019, 12:43:31 am »
If you have the budget, 4 channels can be nice. I have a 4 channel scope but I very rarely use more than 2 channels. Better to have channels you don't need than need channels you don't have. Depending on your use case though 2 channels may be enough but I would only go that route if budget mandates other priorities.
 

Online Fungus

  • Super Contributor
  • ***
  • Posts: 9738
  • Country: 00
Re: Buying a 2CH vs 4CH Scope
« Reply #7 on: March 29, 2019, 01:00:27 am »
Three channels is probably the optimum but they don't make many of those.  :popcorn:

Better to get four, just in case.
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 15383
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: Buying a 2CH vs 4CH Scope
« Reply #8 on: March 29, 2019, 01:21:50 am »
IMO it's not just 2 vs 4 channels but what you get in a DSO's total package as to if the 2ch and 4ch models offer the same features.
If you already own a 2 ch scope then there are ways to use another 2 ch unit to get the info you need and still get close timing relationships with Trig In/Out etc.

I can count on one hand the times I've needed 4 channels and I wouldn't have needed 4 if I used 2 scopes.
For example, a digital control circuit triggers some current draw on an attached part of a design and you need to monitor PSU behavior when it's at both levels of current draw; idle vs a digital event.

For full duplex decoding, 4 channels is a must while just 1 bus decoded with a 2 ch model still can be useful to see if you've got the code right.
Avid Rabid Hobbyist
 

Offline SilverSolder

  • Frequent Contributor
  • **
  • Posts: 538
  • Country: 00
Re: Buying a 2CH vs 4CH Scope
« Reply #9 on: March 29, 2019, 01:34:21 am »
An alternative to a 4 channel scope is a 2 channel + digital MSO.   

The mix of analog and digital on the same display is an awesome capability in its own right, but here's the thing:   The digital channels have adjustable trigger levels - so they can be used to keep track of analog signals too, in many cases.

All of a sudden, you have a LOT of channels to play with!

A MSO is a perfect tool for playing with Arduinos etc. with ADC, DAC, PWM, etc. peripherals.  For example, you can dedicate one of the digital channels to read a pin on the micro that you flip from software, so you can sync what you see on the scope with what your code is doing.  Did that analog voltage stabilize completely before you read it?  -  is it marginal?  - the MSO will tell you.  (So would a 4 channel scope in this example.  But let's say we have 10 PWM channels.  The MSO can show when all 10 pass a certain voltage, for example - in parallel!)
 

Offline Muttley Snickers

  • Supporter
  • ****
  • Posts: 1954
  • Country: au
Re: Buying a 2CH vs 4CH Scope
« Reply #10 on: March 29, 2019, 01:41:54 am »
Only on one occasion have I needed more than two channels, I was working on a timer/ counter project and ended up saving a reference waveform in memory and then used the live signals to compare against. I would expect that most current scopes have this feature and ability to recall and overlay different signals, my old Tektronix TDS-1002 has this feature along with a real time clock which some today don't even have. 
 

Offline slodat

  • Contributor
  • Posts: 27
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #11 on: March 29, 2019, 01:51:47 am »
I’m tuning servo drives on a cnc machine. Monitoring an analog output on four motor at once, looking for the following error on each, at the same time. Completely impossible on a 2 channel scope. I use oscilloscopes for this sort of field work the most. I vote for the four channels with logic inputs.
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 15383
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: Buying a 2CH vs 4CH Scope
« Reply #12 on: March 29, 2019, 01:55:06 am »
An alternative to a 4 channel scope is a 2 channel + digital MSO.   

The mix of analog and digital on the same display is an awesome capability in its own right, but here's the thing:   The digital channels have adjustable trigger levels - so they can be used to keep track of analog signals too, in many cases.

All of a sudden, you have a LOT of channels to play with!

A MSO is a perfect tool for playing with Arduinos etc. with ADC, DAC, PWM, etc. peripherals.  For example, you can dedicate one of the digital channels to read a pin on the micro that you flip from software, so you can sync what you see on the scope with what your code is doing.  Did that analog voltage stabilize completely before you read it?  -  is it marginal?  - the MSO will tell you.  (So would a 4 channel scope in this example.  But let's say we have 10 PWM channels.  The MSO can show when all 10 pass a certain voltage, for example - in parallel!)
Great points.  :-+

However when budget constrained to where a 2ch model is a so much cheaper option, don't forget to factor in the additional cost of;
1 Logic probe HW
2 MSO licensing
These additional costs will make the 4ch model the cheaper option especially in the entry level range of products.
Avid Rabid Hobbyist
 

Online Fungus

  • Super Contributor
  • ***
  • Posts: 9738
  • Country: 00
Re: Buying a 2CH vs 4CH Scope
« Reply #13 on: March 29, 2019, 02:11:37 am »
A MSO is a perfect tool for playing with Arduinos etc. with ADC, DAC, PWM, etc. peripherals.  For example, you can dedicate one of the digital channels to read a pin on the micro that you flip from software, so you can sync what you see on the scope with what your code is doing.  Did that analog voltage stabilize completely before you read it?  -  is it marginal?  - the MSO will tell you.  (So would a 4 channel scope in this example.  But let's say we have 10 PWM channels.  The MSO can show when all 10 pass a certain voltage, for example - in parallel!)

Yep, I use my 4-channel 'scope as a debugger. eg. Flip an I/O pin in an interrupt handler when something occurs, watch it on the scope to make sure it's happening (and when).

It's not 100% about "necessity". When you have four channels you simply have more room to do stuff, it makes life easier.

 
The following users thanked this post: SteveyG

Offline Old Printer

  • Frequent Contributor
  • **
  • Posts: 514
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #14 on: March 29, 2019, 02:32:30 am »
Thanks for all the opinions and examples. Many first time scope buyers are not even sure why they need a scope or what features they need in it. Without a specific use for a scope, the 2ch - 4ch choice is even less clear. I was hoping to get actual examples of when the 2 extra channels came in handy or necessary, or didn't, so that beginner EE buffs could see what might be down the road for them. The responses have been great, please keep it up.  :-+
 

Offline Brumby

  • Supporter
  • ****
  • Posts: 9066
  • Country: au
Re: Buying a 2CH vs 4CH Scope
« Reply #15 on: March 29, 2019, 02:46:08 am »
This is what I ended up doing for more than 2 channels of scope:


On the other hand, it's been quite some time since I've had any need to go that far.

However, if I had the funding to do so, I'd be looking at modern scopes with a definite bias towards 4 channel - even thought the vast majority of occasions, the need has only been for a single channel.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 8721
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #16 on: March 29, 2019, 04:55:41 am »
The last time I used more than two channels I was looking at the clock, data and strobe lines out to some shift registers. Of course I could have used a logic analyzer, arguably a better tool for the job. At least 70% of the time I'm using only a single channel, most of the remaining is two channels.
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 29272
  • Country: au
    • EEVblog
Re: Buying a 2CH vs 4CH Scope
« Reply #17 on: March 29, 2019, 05:03:31 am »
Go for 4CH because it's just so cheap these days.
Just being able to do basic stuff like monitor one or two power rails whilst checking some digital signals is super valuable.
Tons of stuff has more than two power rails these days, so right there a 2CH scope is limiting.
 

Offline Psi

  • Super Contributor
  • ***
  • Posts: 7132
  • Country: nz
Re: Buying a 2CH vs 4CH Scope
« Reply #18 on: March 29, 2019, 05:22:06 am »
Having a 2CH will annoy you to no end when you need to compare more than 2 signals.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline maginnovision

  • Frequent Contributor
  • **
  • Posts: 906
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #19 on: March 29, 2019, 05:44:36 am »
If you can afford it, go 4 channel. If you can't afford it, just get 2. Really recommend saving for 4 though. For the difference in price it's sort of a no brainer because just one time you need 3 or 4 channels and it's worth it.
 

Offline jackbob

  • Regular Contributor
  • *
  • Posts: 167
  • Country: us
    • My YouTube Channel
Re: Buying a 2CH vs 4CH Scope
« Reply #20 on: March 29, 2019, 06:57:33 am »
One of the most compelling reasons to go for 4 channel (at least for me) is to get differential measurements on the cheap. Differential probes often cost more than scopes and surely more than any budget scope. With 4 channels you can get a "semi-differential" measurement using two channels and the math function to obtain the difference. Having 4 channels available means you can get two differential measurements simultaneously, with a two channel scope you can only have one. This is especially useful if you want to plot voltage and current on the same screen and don't have unlimited cash for a current probe. You can use one probe to measure voltage and two other channels to measure the voltage difference across a shunt resistor and obtain a current measurement. While you can achieve this with a two channel scopes in very specific circumstances, it is often useful to have the freedom to make differential measurements anywhere in your circuit . In any case, keep in mind all the ground clips are common.
 
The following users thanked this post: SilverSolder

Offline EEVblog

  • Administrator
  • *****
  • Posts: 29272
  • Country: au
    • EEVblog
Re: Buying a 2CH vs 4CH Scope
« Reply #21 on: March 29, 2019, 07:24:40 am »
If you can afford it, go 4 channel. If you can't afford it, just get 2.

A 4CH scope is only US$375
 

Offline jackbob

  • Regular Contributor
  • *
  • Posts: 167
  • Country: us
    • My YouTube Channel
Re: Buying a 2CH vs 4CH Scope
« Reply #22 on: March 29, 2019, 07:48:13 am »

A 4CH scope is only US$375
I must agree with Dave here. You can pick up a "classic" Rigol ds1054z 4ch budget scope for $375 today. The price difference between that scope and any other digital 2ch budget scope is minuscule. Siglent also produces the SDS1104X-E for about $500 with MSO capabilities and "super phospher" display. The cheapest comparable 2ch scopes I can find run about $300, please do yourself the favor and spend the extra $75 for 4 channels.
« Last Edit: March 30, 2019, 12:22:06 am by jackbob »
 

Offline maginnovision

  • Frequent Contributor
  • **
  • Posts: 906
  • Country: us
Re: Buying a 2CH vs 4CH Scope
« Reply #23 on: March 29, 2019, 08:27:11 am »
If you can afford it, go 4 channel. If you can't afford it, just get 2.

A 4CH scope is only US$375

I know, but there are those penny Pinchers out there.
 

Offline jackbob

  • Regular Contributor
  • *
  • Posts: 167
  • Country: us
    • My YouTube Channel
Re: Buying a 2CH vs 4CH Scope
« Reply #24 on: March 29, 2019, 08:40:51 am »
I believe there are some threads floating around on the forum with discount codes for places like TEquipment and other popular equipment vendors. I have heard of people picking up 4ch scopes for under $350. You might even be able to score a used 1054z for under $300 if you are vigilant  on eBay.
« Last Edit: March 30, 2019, 12:19:09 am by jackbob »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf