#14 Oscilloscope Messungen Teil 3(5)

Hello my dear friends and welcome to our video channel today we want to see our new topic ACDC coupling or direct voltage alternating voltage coupling and the associated determination of a forward voltage level in a signal and today you can play with the digital auscilloscope that I want check a measurement function offered by a digital auscilloscope that cannot be used in analog form, the

oscilloscope

does not have it built-in. I found many that I hadn't done. Let's see what that was. It has a selector switch at the input, which is one per channel. The switch does exactly that, now we can see it in a basic circuit diagram.

Here we can see that the input impedance is defined somewhere, usually a. Mac, that's not so important and here you can use this switch to choose whether the signal goes directly to the Engels. The amplifier is then coupled to the goat so that the forward voltage signal is transmitted to the bypass plates in the analog

oscilloscope

s or whether to have a series capacitor at the input, which is in the nano range typically depending on what you have. the amplifier for the input. If you only have a coupling here, so only the alternating voltage component is transmitted, the direct voltage component logically remains and the capacitor is glued, which means that if there is 10 times direct voltage here, we only have direct voltage here , only here also comes the superposition of the alternating voltage, then that would be an alternating voltage coupling or wiring.

This results in the following technical data for the digital amplifier for the Y axis in the continuous or direct voltage coupling position, I have a frequency range of 0 to MHz -3 DB which means the Minister 3 dB also refers to the two hearts meaning two hearts frequencies when a coupling is attenuated by 3 dB, 3 dB is half the power or 0.7 times the voltage, which is a typical RC high pass, that means when I zero. If I want to have attenuation or dB errors, I have to connect at least double or triple the frequency here, which means that from 10 cores, this input in a coupling is error-free.

You must be careful with very slow signals or with signals in the DC voltage component. By the way, I'm thinking of right side signals. , this lower limit can cause two heart problems, we will only see it, but in principle the change between direct voltage and alternating DC coupling voltage is responsible for the fact that the lower limit frequency is once 0 hertz, so the direct voltage or two hertz, let's focus first on the analog representation. Here I have a signal of unknown amplitude, unknown frequency and unknown forward voltage component i.e. the function generator, we assume a black box and then we will see what is in it.

To the extent that reasonable values ​​come out, distraction purchases are efficient at 2 volts per division of the vertical and wood purchases are at 0.2 microseconds per division 0.2 milliseconds Sorry 0.2 milliseconds so 200 microseconds per division when connecting the last signal we have. See this again for clarity, this is the zero line, so if there is no input signal and it is connected to ground for this purpose, you have parallel here. In addition to the input, another option has been created using a switch to connect the input to ground, so if I press it here and it goes to zero.

This is an input that is connected to ground. Now I can see that there is a signal here. It is obvious, as you can see, that the zero line is not exactly in the middle of the signal. I went up a little bit, my safe amount and now let's think about how we can determine this amount. By the way, we can read the frequency briefly, which should be almost exactly two killer hearts. 0.2 microseconds 0.2 milliseconds per division is 0.29 So 0.5 milliseconds. it has a period of 0.5, so it will be two Killerz, but it's not that important. At the moment we are only interested in the DC voltage level and where does that glass voltage mirror come from or where can it come from? reasons, but one of the most common is simply the circuit design, we always have an example like simply a transistor amplifier in the core circuit.

A base voltage is set here, I have assumed an operating voltage of 12 volts, everything is sized. via pi times pigeon pi times here it will be approximately when it corresponds to the voltage of 2 volts and now 12 volts, I am left with about 5 volts and another 5 volts left in the transist so that we can put a collector voltage of approximately 7 volts in the idle state . The prerequisite is that the base voltage here is about 2.6 volts. It's not important to us at all, we just know that the collector voltage on the transistor in this circuit is relatively high and close to the. operating voltage Here we have the input stage of the following amplifier, which again we have 2.6 volts, if it is 2 volts exactly as assumed here, then this electrolyte capacitor would be a full capacitor.

You must be wondering what polarity you should clearly have here. I have more voltage here I have more 7 volts I have more 2.6 volts so you have to have positive poles here That is simple and obvious, the question is only if I don't know what the voltage is here and I am controlling the amplifier, how do I measure the voltage level CC here, how do I determine it? You can use the voltmeter, that will also work, as we can see. With the oscilloscope you don't have a graphical representation and maybe you can see it. a little bit more, especially when the system is running, so if you have these stereo amplifiers, something like that, you can also measure the voltage here during operation, so let's take everything together and I want to measure the DC voltage, so I need a DC which I wanted then I can get difficult if I want to measure the voltage with a DC voltmeter if I have superimposed alternating voltage so let's go back to our simulated signal that we know something that has approximately a DC voltage and that's another example in terms of magnitude , but the measurement here is relatively easy.

I'm measuring here with DC voltage coupling and I have the signal here. If I now switch from DC voltage coupling to AC voltage coupling, then I see that the switch needs to be cleaned. then I see that I am changing the signal again DC voltage coupling AC voltage coupling the signal has shifted now the question is how much do I choose a reference point here note the voltage which is two four which is 6.4 if we we set at this point is exactly 4 volts so the voltage here will shift down by 2.4 volts when I switch to alternating voltage coupling which means I have a DC offset as they say or a DC offset voltage 2.4 volts.

You can do the measurement. A little easier by putting the signal in Vertical position, it doesn't matter where the oscillogram is located, you can also say I'm going here, now I'm putting the curve there, I can even stretch it a little. I don't do xposition, I push the signal a little bit and now I go to AC, so we remember that point which is 2.9, plus a graduation line, 2.4 volts. I have to move the sign down. I can now measure. I can say that I am. If you are going to measure the voltage from here, you will notice the point to DC switch.

I'm set to 2, 4, but a little too low, go up a little bit more, so now it's a little spongy, we have 2.4 more volts here, which means this 2.4 volts is the DC voltage component of the signal I can determine this way. It's important to note that the cutoff frequency of this system here is around 10 Hertz, which means I'm doing very, very low frequencies. a measurement error because this method does not work, but in practice you have frequencies well above 10 Hertz and that does not matter. Here the same signal is shown on a digital oscilloscope, we see here that the zero line is marked, this is the arrow, the signal also shifts slightly up, we also have 2 volts per division per division here if you now switch from the coupling switch from DC to DC to a coupling, it's not that easy, of course it was an idiotic thing, that's DC, I go to the coupling and immediately we have a jump down and if you look at the voltages again closely, I also go a little here.

Let's go back for a moment to DC coupling as if we were exactly on the line now. I'm going to couple, we're a little bit below the line, a little bit more than two bolts down there which is also this 2.2 or 2.4 volts that we had before, we also have the same order of magnitude here, that fits pretty well . I go back to docking, the menu is always completely removed from the menu and now there is an interesting possibility with these types of digital oscilloscopes that you can do calculations because what we see here is not analog.

Track how an analog roscope delivers them. , but these are numerical values ​​that are displayed at the socioscope input. Here is an AD converter that converts this analog quantity into digital values ​​into numerical values ​​and you can calculate numbers beautifully, you can represent them. them graphically and then doing it is like it's a sine again, but in the end it's just a collection of numbers that become binary, but you can calculate with it and there are several mathematical functions, there are subfunctions and one is masher here and there now I can make different measurements in the vertical area and one of the measurements is the average that I wanted to average and you can see the shapes showing up again.

I could make it a little bigger so you can see the formula. which is the sum of all the values ​​from 1 to n, then by means of a for the three to determine the means, the voltages do each measurement point in this way and form an average value and then show the average sword as a value average and that is exactly the linear average value which also corresponds to the superimposed DC voltage. Now we have the average voltage display here and we are also reading 2.2 volts here and now I would like to show you the little trap that you have here.

It's not actually mentioned. In any manual for such calculations, of course, the oscilloscope must contain complete oscillations. This means that the start point here and the end point here must match, if they don't, if the image doesn't show a full swing or an integer multiple of it, then you have significant measurement error here. I'll show it now by simply taking the change in frequency and we immediately read a different voltage. Now I'm going to focus a little better so you can see it a little bit. better, now we have shown here about 1.9 volts, the voltage will change, which means that this display here changes very strongly with the frequency of the voltage because of course full periods are no longer shown here and you have to be very careful when doing this .

You do calculations like this, the computer there is frozen, it calculates it and says the average from there to there is this point value from there, but under Circumstances it does not correspond to what you have in practice because the signals always have to be represented. very little, i.e. all the oscillations, the computer has little interest and does not do a bladder tender test or anything like that, it shows that there has been an explosion and the old one is applied. For example, here is 2.4 volts and whose note frequency does not change from level 2.1 to 2.01.9 volts, which means that this average with such digital oscilloscopes should be viewed with extreme caution, as should all calculations .

For example when doing power calculations from sine curves you should always make sure you have complete sine curves otherwise the computer will calculate shit because it said the picture you gave me and it doesn't know anything about it but it does it with coldness. The following applies to such measurements. As with all measurements you have to be prepared, don't just believe what it says, start by using a calculator, don't plug in any numbers and then be satisfied with the result, you need to check the magnitude and think about That may be true, that is always true. very helpful it is very easy to make typos or make a mistake in the menu and select the completely wrong voltage or select the wrong calculation program so asking my question may be true and if you look here that here is 2 volts per division, so you can roughly estimate that the average value is maybe actually in the middle, between the peak and the peak on a sine wave and then you have about 2 volts as the average voltage as the forward voltage value and that's fine and now Let's look at it in a really interesting way.

Here we have a real signal that is symmetrical to the zero line. I may have to recalibrate my function generator. If I do DC coupling, the signal shifts down a bit if I switch to AC. If you go, you can see that it slides up a little bit, that means there is also a small component, it's not much, but it's noticeable. The calculation of the average value says approximately - 170 mv. Well now you might think that at 2 volts per division that might be correct, although here too of course you would have to pay attention to the frequency as the frequency fits perfectly, but it doesn't.

That's how bad now I want one to show another effect. What happens if you have relatively low frequency right oscillations that have a high voltage componentstraight? So there are problems with this measurement method. We have shown this signal correct with the and this way we now have a total of two kilohertz as before Offset of almost exactly two volts, so we have two volts per division again, so the 4 volts, the average is about 4 volts , right in the middle it says the system, the frequencies fit here is the beginning and here comes the next starting so you can say The periods can be displayed completely so the average calculation makes sense so you can live with it if we now do the measurement from the DC voltage level with the known method switching to AC coupling, what was that?

Then we immediately see that the trigger is not correct, the level of the carrier, which is the signal, has dropped by exactly 2 volts, which corresponds to the signal that we expected 2 volts DC and now I reduce the frequency, now we are at 20 Hertz, so we turn it up. a bit here, the DC coupling is still in place, 4 volts matching almost exactly, now I'm using too much AC, so of course the problem is that the coupling destroys the signal for me, that's a known problem If it correctly displays signals with a long period that pass through a capacitor and there are problems and there it is no longer so easy to measure how high it is, the displacement of the signal.

With a little trick, you can still take the leading edge as a. reference and say well, that's it, but it's not completely clean either. The bottom edge is there too. Also next to it again, that is, by flattening or tempering the ceiling with this method at very low frequencies, especially at the correct frequencies, it is achieved. It's very difficult and that's where the fun ends. The measurement method here is even more reliable if you get the number of periods correct. To illustrate the problem a little more drastically, I looked at the frequency up to two hearts, two hearts square wave. frequency, this is the limit frequency specified in the data sheet and now we want the DC coupling here, we have the signals at the same height, we still have an average value of 4, 0, that's fine, now I do a coupling, it what happens to the signal looks like yes or how many volts they have that the signals move with the simple method.

I make a note of one point and then I go down and say, okay, that's the value I'm told and how much the image has shifted, there's no shifted image, the image is folded, which is the original image and if I wanted four pins of DC voltage would have to be able to lower the signal by 4 volts, only there is nothing we would like to lower, the tip will be later Stream episode 3 I can't do much and what's behind it is that it can't be used with the frequency of treble, we were still able to read a little bit of something here that no longer works at all, which means this measurement method. not possible with a square wave signal with a low repetition rate.

It can be used in particular where there are sloping ceilings, so if the correct signal drifts, then the fun stops and nothing can be measured with this method anymore. The negative sign is shown here. 160 mg, which is actually pretty good for the rectangular, I know it's almost zero. I also don't know if the ratio is ideally perfect, so I would also be careful with the function generator I have here, like I said. , I always want to compare it, but that is not the problem and last but not least, a parade of champions, we have the signal again with two killerherz what the Baltic Sea says a displacement of 2.172.18 the analog multimeter that is connected in parallel you have to read 2.25, so 2.5 is total, we are above 2.25, which says 2.28 and the scope here with the well-known measurement method had a voltage jump of about 2.4, just under 2.4 volts, it is also there.

Now I'm listening to frequency factor 10 to show what's happening, probably nothing will happen because the higher frequency doesn't affect these instruments as long as it's not in the megahertz range. We still have it 2.17 something like that, the same rash, the same rash and here the same image, now it's 20 kilohertz, I'll go to 200 kilohertz, nothing changes here either, nothing really, no wonder because these devices are in the range DC measurement. Certainly, there are underpasses installed in the entrance area. Low RC is better for filtering. it eliminates any tree voltage so I think they should go up to this frequency range as long as the measurement leads are reasonable.

Only at low frequencies below two 200 Hertz, that is 20 hearts. Here you can see if the pointer is flashing, the. The pointer makes its first vibrations, I don't know if that can be seen on the camera, of course, if I go down to two hearts then you are doing shit anyway and the two oscilloscopes are somewhere next to each other, then you would. then you have to switch to the glowing cell phone case. Here you can see something again, okay, I think it was a good demonstration of what the cpugel can definitely measure with such instruments here, which works, but like I said, you have to pay attention to the frequencies This brings us to the end of the Part 3 on Telescope Series Oscilloscopes Measurements Today we saw how DC voltage components and AC voltage components can be measured separately using the coupling function on the AC or DC coupled input.

I hope it was a bit of fun, it was informative, stay healthy and I'll see you again on this channel.