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Just was thinking to buy an oscilloscope, thus went to a shop and started to rummage all of the shops to buy an osci. which could be suitable for me. Read specifications of them. Some features was clear to me and I know them. e.g. sample rate or frequence and I know why the price of oscilloscopes. increases with increasing these parameters and I know what range of these parameters could be suitable for me but there is a question that I couldn't find any answer for it on the net. Why do some oscilloscopes have several input channels? I know with this feature you can capture several signals at the same time but the main question is that when do you need such a feature? I'm thinking that when do I need to capture several signals at the same time but couldn't find the answer. Maybe you could clear me out.

I guess we cannot find any Oscope with less than two channel. Why?

Please post your answer with your experience about what made you to purchase an oscope with more channels. As you know, Oscops with more channels are expensive and so couldn't find anybody ovehere that has oscope with more channels.

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    \$\begingroup\$ Because the relative time difference between several channels is paramount in most measurements, something you can't see with only one channel. \$\endgroup\$ – winny Feb 7 at 8:49
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    \$\begingroup\$ Rather obviously, so you can see several signals in a circuit at the same time and see their relation to each other. \$\endgroup\$ – Unimportant Feb 7 at 8:49
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    \$\begingroup\$ To view both current and voltage on a component, to simultaneously check both the input and the output of a block, to produce a X-Y graph, to use one channel as a trigger, etc... really, electronic engineering would be much more difficult if all oscilloscopes had only one channel. \$\endgroup\$ – dim Feb 7 at 8:53
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    \$\begingroup\$ Thank you but it's not a good suggestion because of low SR and bandwith I never claimed that this one-channel scope is a good buy. You asked if any existed and they do. These hand-held low BW scopes are only for very specific applications and/or if you really cannot afford anything better. \$\endgroup\$ – Bimpelrekkie Feb 7 at 9:01
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    \$\begingroup\$ Measure one signal. Remove probe and measure another signal. Now tell how they relate in time to each other? \$\endgroup\$ – winny Feb 7 at 9:13
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A use case is where I want to simultaneously observe (for example to observe time delay) the input and output of a differential amplifier.

I could use differential probes but I would need two and these can be expensive.

If I had a 4 channel scope I can do this:

I connect scope channels A and B to the in+ and in- inputs of the amplifier. Then on the scope display A-B which is the differential input signal.

At the output I connect channels C and D to the out+ and out- outputs of the amplifier. Then on the scope display C-D which is the differential output signal.

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  • \$\begingroup\$ +1 For sharing your experience. \$\endgroup\$ – Roh Feb 7 at 9:05
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You're right - the main reason to have multiple input channels is to be able to measure several signals simultaneously. A two-channel oscilloscope lets you compare an input signal to an output signal, and if you had a means to control the behaviour DUT (device under test) in between the two probes then being able to see the input and output simultaneously can help you make better decisions on its performance.

EDIT: To give another example, you can use one channel to trigger on an activation signal (for example, a pin select) and another channel on an input or output pin. Having both on screen at once allows you to measure the delay from one event (the trigger signal) and another (the input/output signal).

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  • \$\begingroup\$ Thank you but some users named winny and @dim have made some good comments that I interested to hear them. \$\endgroup\$ – Roh Feb 7 at 8:56
  • \$\begingroup\$ @roh Me thinks that winny and dim have made their contribution and moved on. No real point in a scope that can only look at one signal. Similarly, most scopes with two inputs have an external trigger, so you can look at two signals relative to an external reference (which could be one of the two signals or another signal), so 3 signals. I find that if I have two, I sometimes need more. \$\endgroup\$ – StainlessSteelRat Feb 7 at 16:26
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I think another important aspect is that oscilloscopes have a common ground in every channel, so if you have a 1 channel oscilloscope you can only measure things that are connected to ground on one end. Making you unable to measure signals from anything that is separated from the reference, with two channels you can use two probes, measure the voltage at two points and while it is a bit of a workaround you can measure the voltage of any component in a circuit.

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Also, some scopes have digital inputs. Just as having two or more analog inputs lets you see the relationship between two analog signals, scopes that have digital inputs allow you to see the relationship between digital and analog signals in your design.

For example, you might want to know how long it takes for a digital-to-analog converter (or analog to digital converter) to settle, once you've set up the input.

In addition, you can track what's happening as code executes in the digital domain, and see how it's affecting the analog domain (the output). All very useful. Hope this helps!

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