Buy a real analog oscilloscope pleaseeeeeeeeeee !

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SemiconductorCat
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Buy a real analog oscilloscope pleaseeeeeeeeeee !

Post by SemiconductorCat » Sun Mar 09, 2014 3:00 pm

I'm not bring you guys back into the CRT oscilloscope times. But if you are serious in analog electronics , then you better avoid two fancy test equipments if you are a newbie.
1. Digital Multimeter.
2. Digital Oscilloscope.

The reason is very simple in the first case. Where digital multimeter is a very sensitive device, with large input impedance, Oky wait a minute... is that large input impedance is bad thing? Of course it's not. But the problem is it does have very low damping factor on high frequency oscillations which would make it's somewhat impossible to take measurements without a hold function, even with using the hold function, the measurements would not be precise.
However you could always add some damping to it. But in that case you need to know what you are dealing with.
digital multimeter typically does have 10MOhm of input impedance on their input probes. No need to say that such a large R value in a lump network would cause very high Q value. Where what you need to do is to do is synthesize a RC low pass filter with very low Q factor. I may need to write another dedicated article on how to do this in a separate article.

Sooo, if you know your circuit and if you know what you want to measure, digital multimeter is good for you. But it's for professional useprefered for professional use of circuit designer[who knows how it work]. What I'm trying to say is , if yo are hobbit and little a newbie to electronics then you better avoid that fancy tool.

[Note tools are always your tools. A good technician or an engineer does not buz their tools, instead they prefer the right tool for right thing. Also need to mention that some digital multimeter come with advanced features like ESR meter, capacitance meter . In a case you are doing electronic shop, such tools would make your life a lot easier, example , when you need to check a capacitor without removing it from the board.]

The next thing that I told you to avoid is the digital oscilloscopes. The reason is ___,
Simply as a student you don't have money to buy a professional level oscilloscope. If you could buy a professional grade oscilloscope then it's fine.

Let me show some products in ebay which you should avoid.
1. DSP nano DSO203, DSO202 , DSO201
2. Other cheap oscilloscopes like these too. Like this.
Oh it's hantek , and hantek is a good reputed brand name. Well the problem is hantek DSO's are really expensive than this. I mean the hantek real digital oscilloscope. The reason is they are based on real Flash Analog to digital converters
instead other techniques.

Real fast A/D converters are really expensive than we think. It's not even economically feasible to manufacture digital oscilloscopes with these flash ADC. Well however fortunately there are other methods and techniques that they could use.
* taking the value of the signal at different moments of the signal and combining them to render full waveform.
* Using the divide by 2 method.
Using these methods would does need somekind of sample and hold circuit. Sample and hold is a very common circuit configuration. refer : http://en.wikipedia.org/wiki/Sample_and_hold

Image
Well you may also see Dave's peak detector circuit explanation bellow for more knowledge.
[media]https://www.youtube.com/watch?v=jllsqRWhjGM[/media]
However let's come back to our discussion. Oky now we know flash ADC's are not cheap and even professional oscilloscopes does not sometimes use them fully instead they use some techniques. So what is the problem with that?

Well when oscilloscope probe takes different currents at different sampling moments it would leads to distort the signal. Even the sample and hold circuit have large input capacitance than complete flash ADC. The standard oscilloscope probe that we speaking , which is 15pF capacitance is no longer valid there. Instead you could find higher capacitance. Please take a look at the DSO201 and DSO203 review bellow. That happen due to this internal capacitance.
[media]https://www.youtube.com/watch?v=SOdGPUGi9wQ[/media]

So my final argument does agrees with Dave. PLEASE buy a real analog oscilloscope please !
That's the same argument with Dave. Well first I head it, I wondered why ? And I did this research.
[media]https://www.youtube.com/watch?v=Xh9FNRpta9s[/media]


But what DSO201 or DSO203 is best for.
DSO201 does said it does have 200Kb sampling rate so it's only better to scope signals bellow 50Khz.That's a pretty good pocket tool for a one who in the audio industry. For a example you could take that in your pocket to the site and fix the AC 50Hz interference from a ground loop on a audio amplifier. It's a great tool for a disco DJ on site technician.
DOS201 is not even better for one who follow a course switch mode power supply design. Instead you could buy DSO203 for that. DSO203 is a good tool for less than 500Khz. 500Khz signals would render nicely by the DSO203. Anything beyond , if you are serious into your studies in engineering, such as into microwave engineering and communication well that's not the tool for ya.
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Re: Buy a real analog oscilloscope pleaseeeeeeeeeee !

Post by Neo » Wed Mar 12, 2014 9:17 pm

This is indeed a nice review Semi. Excellent article!!!
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