Author Topic: Oscilloscope number of probes  (Read 386 times)

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Offline Yaroooo

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Oscilloscope number of probes
« on: October 18, 2019, 03:55:21 pm »
Hi all,

I've read a lot of topics with some people that advise 4 probes with less bandwidth (100Mhz) and some 2 with higher bandwidth (300Mhz). With a fixed budget I must choose one of this options.

People that advice 4 probes used this feature to analyze SPI and multi signals. But I've through about speed of this signals and purpose of the oscilloscope. If I exclude space or 2in1 pros where for me are not a problem. Isn't better to have a more reliable oscilloscope on this speeds and check each signal at time? Once I've found that they act correctly without disturbance I can analyze/read them with a Logic Analyzer that allow me more I/Os.

Same apply for all signals that must be analyzed on logic level. Once checked, they can be actually read by a logic analyzer that also simulate a counterpart.

I just want to expose what are my consideration on my use of this instrument. On lower budgets that seems more logical. I'd like to know also other opinions about this.
 

Offline rstofer

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Re: Oscilloscope number of probes
« Reply #1 on: October 18, 2019, 05:42:01 pm »
It is certainly possible to get along with a two channel scope (and 2 probes of equivalent bandwidth), it was done that way for decades.  It's a fairly recent development that 4 channels isn't a lot more expensive than 2 channels.

Given a 2 channel scope, you can make the case for a logic analyzer and, in fact, if you had more than 4 signals to watch, it wouldn't matter which scope you had, if it didn't include a logic analyzer, you would have to buy one extra.

A good logic analyzer of some kind is quite helpful in digital electronics whether you have a scope or not.

Your approach of using a high bandwidth 2 channel scope to check signal integrity (and timing) and following up with a logic analyzer is correct.

I used a 2 channel scope off and on for over 50 years and I still have a 350 MHz Tektronix 485 for the high speed stuff.  My 4 channel Rigol DS1054Z was a nice addition.  Today, I would be looking at the 200 MHz Siglent offerings.  I would probably still go for 4 channels.  More is always better.
 

Offline TheHolyHorse

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Re: Oscilloscope number of probes
« Reply #2 on: October 18, 2019, 08:22:01 pm »
I just ordered an oscilloscope I was choosing between the siglent SDS1202X-E(2 channel) and the SDS1104X-E(4 channel). I went with the 1104 because it wasn't that much more. 400~ vs 500~ euro. If you're gonna spend 400 what's another 100, if you can't afford that right now I'd wait and save up some more. Better to have too many channels than too few.

An oscilloscope is something that wont be obsolete in 5 years unlike PC hw. So it could be worth spending a bit more, it would suck if you realized later that you really needed those 4 channels.
 

Online tggzzz

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Re: Oscilloscope number of probes
« Reply #3 on: October 18, 2019, 10:48:02 pm »
The OP has a better grasp of the important fundamentals than most people on this forum!

Use a scope to ensure signal integrity, I.e. that the analogue voltage/current transmitted between chips will be correctly interpreted as a digital signal by the receiver. Once that is true, switch to debugging digital signals using analogic analyser and printf() statements.

Hence the key parameter of a scope is it's bandwidth. The key issues with logic analysers are the sampling rate and the ability to filter out irrelevant logic levels so that you can see the signal's of interest.
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Offline rstofer

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Re: Oscilloscope number of probes
« Reply #4 on: October 18, 2019, 11:16:50 pm »
And the 1104 can be unlocked to 200 MHz, details elsewhere.  Number of channels is the most important consideration - except for bandwidth.
I already have the Rigol but if I were in the market today, that Siglent SDS1104X-E would be on my very short list.  In fact, it would probably already be on my bench.  Unlocked, of course...

I don't think I would consider the SDS1102X-E - I really want 4 channels and price isn't the biggest factor.


 

Offline TheHolyHorse

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Re: Oscilloscope number of probes
« Reply #5 on: October 18, 2019, 11:41:31 pm »
The OP has a better grasp of the important fundamentals than most people on this forum!

Use a scope to ensure signal integrity, I.e. that the analogue voltage/current transmitted between chips will be correctly interpreted as a digital signal by the receiver. Once that is true, switch to debugging digital signals using analogic analyser and printf() statements.

Hence the key parameter of a scope is it's bandwidth. The key issues with logic analysers are the sampling rate and the ability to filter out irrelevant logic levels so that you can see the signal's of interest.

If all you did was digital you'd probably be fine with 2 channels and a logic analyzer, but you wont always be probing digital stuff. So when the price difference isn't big I'd go for the 4 channel one. You can't go wrong with more channels.
 

Offline German_EE

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Re: Oscilloscope number of probes
« Reply #6 on: October 19, 2019, 04:59:59 pm »
Take one four-channel scope, channels 1 and 2 are on the amplifier left and right inputs and channels 3 and 4 are on the left and right amplifier outputs. Checking stereo amplifiers is now a lot easier than it used to be.

Or.......

If you work on power supplies then channels 1 and 2 monitor the input voltage and current and channels 3 and 4 monitor the output.

Or.........

Timing. You have a transceiver that keeps on blowing one particular component when you change between receive and transmit. With four channels you can monitor receive power, transmit power, the line driving the antenna changeover relay and the output RF level

Or..........

Video. Four channels means that you can monitor red, green, blue and sync

Or..........

Stepper motors, damn useful if there are four phases.

I didn't think I would ever use all four channels but the full set of probes probably gets plugged in about once a month and I would never go back.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline Mortymore

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Re: Oscilloscope number of probes
« Reply #7 on: October 19, 2019, 07:38:16 pm »
And to keep in mind that 4 ch scopes come with 4 probes. So the 2 extra probes if bought separately would cost, lets say €50
So the €100 difference price between the 2ch and 4ch Siglent scopes mentioned, is actually lower for the scope itself.

The probes that come with the Siglent SDS1104X-E (100MHz), are told to still be very good if the scope is hacked to 200MHz. Another thing to keep in mind since the probe BW may be a limiting factor if the BW of a scope is hacked, but that's not an issue in this particular case
« Last Edit: October 19, 2019, 07:40:45 pm by Mortymore »
 


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