Everything you need to know when buying/using an Oscilloscope! EB#49

So I finally did it! I just built a crude but functional prototype of a Switched Mode Power Supply that converts 230V AC mains voltage into 5V DC. So let's hook it up and. Thank god. And as you can see nothing blows up and we should be getting around 5V on the output, yes. But let me show you some interesting waveforms on the oscilloscope...... Hold it.....what I was about to do there is one of the biggest mistakes when working with an osilloscope which can lead to a lot of damage. So to make sure that you don't make such stupid mistakes I will tell you in this video everything you need to know when using an osilloscope. This includes all the basics like how to choose a scope and how to do simple voltage and current measurements but also more advanced stuff like safe mains voltage measurements and FFT. Let's get started This video is sponsored by Brilliant! If you ever wanted to learn how to do Arduino programming or computer programming in general, but were put off by the opaque coding language, then Brilliant is for you. By learning with the Algorithms Fundamentals course in which you shift around “pseudocode”, you will grasp a good understanding on how computer algorithms work without having to dig through the weeds of coding syntax. If you want to try it out then go to Brilliant dot org /GreatScott and sign up for free. And the first 200 people that sign up for an annual subscription through this link will also get a 20% discount. First off, let me tell you in one sentence why you would even need an oscilloscope. It visualizes a voltage and or current value over time and since not only power electronics nowadays get switched on and off repeatedly but also data communication protocols with their ones and zeros, it is pretty essential to see those waveforms when building or repairing electronics. And with that being said let's get rid of my overkill oscilloscope that due to its price, pretty much none of my viewers own and instead let's focus on this more budget friendly option which still costs quite a bit of money. Of course you can go even cheaper when buying an oscilloscope but you should always consider the amount of channels, the available bandwidth and the sampling rate when choosing one. The amount of channels is pretty straightforward and determines how many voltage and or current signals you can have a look at simultaneously. I would always prefer a 4 channel scope because there are plenty of situations in which you want to have a look at more than 2 signals at the same time. Next the bandwidth describes the frequency at which the input signal gets damped by -3dB meaning its amplitude value goes down to 70.7% of its original value. As an example my function generator here produces a sine wave with variable frequency and as you can see on the oscilloscope at the higher frequencies of 80MHz the amplitude gets a bit lowered. The reason is that the oscilloscope acts kind of like a low pass filter which not only damps the amplitude but also distorts for example the rise time which we want to avoid. So a rule of thumb is that my 200MHz scope can handle one fifth of its bandwidth with ease, so a signal with a frequency of 40MHz which is plenty for lots of applications. And while the bandwidth is more like an analog value, the sampling rate is a purely digital one. It describes how many measurements the scope can take in a second and let me tell you that 2GSa/s is plenty. I also worked with lower sampling rate models and never got any problems even when we consider that by using more channels the sampling rate splits up. And with this knowledge so far you were able to choose an oscilloscope that suits your project needs and you just unpacked it and discovered 4 of those probes. Those are passives probes and they are super easy to work with; but let's not talk about why I only got 3 of them along with wrong probe heads. To use them; simply hook up the BNC connector, select a scaling factor which is either x1 or x10, attach your alligator clip to GND and use the tip of the probe to touch the point of your circuit you are interested in. And just like that you see something on the screen which we will trigger correctly in a minute but before that let me tell you that the scaling factor either decreases the voltage signal by a factor of 10 or does not change it at all with x1. But that means it comes with a lower resistance and higher capacitance so the bandwidth we talked about earlier is lower. That is why I always use x10 which guarantees the highest bandwidth. Of course we could talk hours about the impedance input of the scope and probes here but to keep it simple let's skip that part and instead let's focus on our scope display. This is a classic example of wrong triggering. The trigger is used in order to create a stationary image of our periodic signal by capturing the waveform at always the same point which can be for example a rising or falling edge. But by pressing the trigger button on the scope and selecting trigger type, we can see that it can also be a certain pulse width, a pattern or a specific rise or fall time. But most of the time the edge option works just fine and by lowering the trigger threshold value into the voltage region of our signal we can see that we got a beautiful PWM signal......whose voltage amplitude is way too low. As you can see my vertical voltage division is 200mV per division which you can by the way change by using the vertical knob. But anyway, my project works with a logic voltage of 5V so why am I seeing around 500mV. This is also a beginners mistake and can be solved by simply choosing the correct scaling factor. And since we talked about the vertical voltage division, we might as well also talk about the horizontal time division which is right now 10us per division. But we can change it down and up as well in order to present our waveform in the best way. With the known time division we can also calculate the frequency of our signal which should be around 33kHz. But to be honest no one does this anymore with digital scopes since they come with tons of measuring features which of course includes measuring the frequency. And if you want to for example measure the rise time of a MOSFET gate which describes how long it takes the voltage to go from 10% to 90% of its intended value than simply hit the stop button, zoom in and activate the cursor function. With it you can select track waveform and you get two cursors which you can now move to the desired voltage value positions in order to determine the time difference between them and thus get the rise time. OK, moving on to a different example in which I now want to see how much voltage ripple this small boost converter comes with on its output while powering a load. Of course we could adjust the offset of the signal and then zoom in but that can be a hassle. Instead we can change the input coupling to AC which simplified speaking adds a small capacitor in series to input of the scope that only lets AC pass. This way we remove the offset voltage and all we have to do is zoom in and use a measure function in order to find out that the boost converter comes with a ripple of 4.2V peak to peak which means the boost converter is definitely not suitable for this job. Now for my last voltage measuring example I want to see how this capacitor charges up but as you can see with the current settings we can not really capture that charging curve. Thankfully all we have to do is to select single mode capturing. Now the scope will trigger as soon as the capacitor reaches the trigger threshold voltage and just like that we got a lovely waveform which we can now analyze. At this point you probably already noticed that a scope can only directly measure a voltage signal. So in order to measure a current, we would either need a current shunt or a current clamp. I actually talked about both of these methods in my recent video about creating a DIY current clamp so definitely check that out if you are interested. But in a nutshell I would always recommend such a current clamp since it is super simple to set up and easy to use. And with that being said you should now be familiar with all the basics when it comes to using an oscilloscope. So let's move on to the advanced section with a mains voltage example and like always I have to warn you that mains voltage can lead to major injuries if not handled correctly. But anyway the RMS voltage value of our mains voltage is around 230V which according to the datasheet of the oscilloscope is above the maximum rated input voltage. But since we are using a scaling factor of 10:1 which would decrease the voltage to 23V and because the probe can handle 300V RMS, we should be just fine. And as you can see by touching a mains voltage point with the probe nothing explodes and all that is left to do is to hook up the alligator GND reference to the reference point which is the mistake you should definitely not do. You see this alligator clip is connected directly to the PE wire of our electrical system through the BNC connectors. And by connecting the PE wire directly or partly to the L or N phase of our electrical system we either trip the RCD in the best case or trip our circuit breaker in the worst case which could potentially destroy something inside our scope due to a high current flow. To solve this problem we can use such differential probes whose input and output is isolated from one another. This way we can hook up mains voltage without having to worry about that something will get destroyed. Now of course when it comes to power electronics which is my specialty then the math function along with the FFT function is also pretty important but to learn more about that I would recommend you to watch my video about all the different kinds of powers forms that exist. With that being said you should now be ready to play around with your first oscilloscope and discover all of its benefits without blowing anything up. As always thanks for watching. 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Channel: GreatScott!

Views: 295,133

Keywords: oscilloscope, scope, basic, basics, electronic, electronics, eb, how, to, use, beginner, beginners, guide, tutorial, diy, do, it, yourself, mains, voltage, clip, alligator, gnd, ground, reference, bnc, pe, live, neutral, protective, earth, short, circuit, mistake, explain, rcd, breaker, destroy, damage, keysight, rigol, passive, probe, factor, scaling, trigger, triggering, edge, current, bandwidth, sampling, rate, channel, amount, buy, get, frequency, cheap, time, measure, cursor, ac, dc, coupling, fft, fourier, greatscott, greatscott!, impedance, clamp, shunt

Id: d58GzhXKKG8

Length: 12min 39sec (759 seconds)

Published: Sun Aug 08 2021