The article will describe in detail how to use an oscilloscope, what it is and for what purposes it is needed. No laboratory can exist without measuring equipment or sources of signals, voltages and currents. And if you plan to design and create various devices (especially if we are talking about high-frequency technology, for example, inverter power supplies), then doing anything without an oscilloscope will be problematic.
This is a device that allows you to “see” the voltage, or more precisely, its shape over a certain period of time. With its help, you can measure many parameters - voltage, frequency, current, phase angles. But what is especially good about this device is that it allows you to visually evaluate the shape of the signal. Indeed, in most cases, it is she who speaks about what exactly is happening in the circuit in which the measurement is being carried out.
In some cases, for example, voltage may contain not only a constant, but also an alternating component. And the shape of the second may be far from an ideal sinusoid. Voltmeters, for example, perceive such a signal with large errors. Pointer instruments will give one value, digital ones - much less, and DC voltmeters - several times more. The most accurate measurement can be carried out using the device described in the article. And it doesn’t matter whether the H3013 oscilloscope is used (how to use it is discussed below) or another model. The measurements are the same.
This is quite simple to implement - you need to connect a capacitor to the amplifier input. In this case, the entrance is closed. Please note that in this measurement mode, low-frequency signals with a frequency less than 5 Hz are attenuated. Therefore, they can only be measured in open input mode.
When the switch is set to the middle position, the amplifier is disconnected from the input connector and a short circuit occurs to the housing. Thanks to this, it is possible to install a sweep. Since it is impossible to use the S1-49 oscilloscope and analogues without knowledge of the basic controls, it is worth talking about them in more detail.
On the front panel there is a scale in the vertical plane - it is determined using the sensitivity regulator of the channel along which the measurement takes place. It is possible to change the scale not smoothly, but stepwise, using a switch. What values can be set using it, look on the case next to it. On the same axis with this switch there is a regulator for smooth adjustment (here's how to use the S1-73 oscilloscope and similar models).
On the front panel you can find a handle with a double-headed arrow. If you rotate it, the chart of this channel will begin to move in the vertical plane (down and up). Please note that there is a graphic next to this knob that shows which way you need to turn it to change the multiplier value up or down. both channels are the same. In addition, on the front panel there are knobs for adjusting contrast, brightness, and synchronization. It is worth noting that a digital pocket oscilloscope (we are discussing how to use the device) also has a number of settings for displaying graphs.
We continue to describe how to use a digital or analog oscilloscope. It's important to note that they all have a flaw. One feature worth mentioning is that all measurements are carried out visually, so there is a risk that the error will be high. You should also take into account the fact that sweep voltages have extremely low linearity, which leads to a phase or frequency shift of approximately 5%. To minimize these errors, one simple condition must be met - the graph should occupy approximately 90% of the screen area. When measuring frequency and voltage (there is a time interval), the input signal gain and sweep speed adjustment controls should be set to the extreme right positions. It is worth noting one feature: since even a beginner can use a digital oscilloscope, devices with a cathode ray tube have lost their relevance.
To measure voltage, you must use scale values in the vertical plane. To get started, you need to do one of these steps:
Switch the device to measurement mode and apply the signal to the input that needs to be examined. In this case, the mode switch is set to any working position. But how to use a portable digital oscilloscope? It’s a little more complicated - such devices have a lot more adjustments.
As a result, you can see a graph on the screen. To accurately measure height, use a pen with a horizontal double-headed arrow. Make sure that the top point of the graph falls on the one located in the center. There is a graduation on it, so it will be much easier to calculate the effective voltage in the circuit.
Using an oscilloscope, you can measure time intervals, in particular, the signal period. You understand that the frequency of any signal is always proportional to the period. Period measurements can be made in any area of the oscillogram. But it is more convenient and more accurate to measure at those points where the graph intersects the horizontal axis. Therefore, before starting measurements, be sure to set the scan exactly to a horizontal line located in the center. Since using a portable digital oscilloscope is much easier than using an analog one, the latter have long since sunk into oblivion and are rarely used for measurements.
Next, using the handle indicated by the horizontal double-headed arrow, you need to shift the start of the period with the leftmost line on the screen. After calculating the period of the signal, you can use a simple formula to calculate the frequency. To do this, you need to divide the unit by the previously calculated period. The measurement accuracy varies. To increase it, you need to stretch the graph horizontally as much as possible.
Pay attention to one regularity: as the period increases, the frequency decreases (the proportion is inverse). And vice versa - as the period decreases, the frequency increases. A low margin of error is when it is less than 1 percent. But not every oscilloscope can provide such high accuracy. Only with digital ones, in which the scan is linear, can such accurate measurements be obtained.
And now about how to use the S1-112A oscilloscope to measure phase shift. But first, a definition. Phase shift is a characteristic showing how two processes (oscillatory) are located relative to each other over a period of time. Moreover, the measurement occurs not in seconds, but in parts of a period. In other words, the unit of measurement is angle units. If the signals are equally positioned relative to each other, then their phase shift will also be the same. Moreover, this does not depend on the frequency and period - the actual scale of the graphs on the horizontal (time) axis can be anything.
The maximum accuracy of measurement will be if you stretch the graph to the entire length of the screen. In analog oscilloscopes, the signal graph for each channel will have the same brightness and color. To distinguish these graphs from each other, it is necessary to make each one have its own amplitude. And it is important to make the voltage supplied to the first channel as large as possible. This will make it much better to keep the image on the screen in sync. Here's how to use the S1-112A oscilloscope. Other devices differ slightly in operation.
▌Old article about an analog oscilloscope
Sooner or later, any novice electronics engineer, if he does not give up his experiments, will grow up to circuits where it is necessary to monitor not just currents and voltages, but the operation of the circuit in dynamics. This is especially often needed in various generators and pulse devices. There is nothing to do here without an oscilloscope!
Scary device, right? A bunch of knobs, some buttons, and even a screen, and it’s not clear what’s there or why. No problem, we'll fix it now. Now I will tell you how to use an oscilloscope.
In fact, everything is simple here - an oscilloscope, roughly speaking, is just... voltmeter! Only a cunning one, capable of showing a change in the shape of the measured voltage.
As always, I’ll explain with an abstract example.
Imagine that you are standing in front of the railway, and an endless train consisting of completely identical cars is rushing past you at breakneck speed. If you just stand and look at them, you will see nothing but blurry garbage.
Now we’ll put a wall with a window in front of you. And we begin to open the window only when the next carriage is in the same position as the previous one. Since our cars are all the same, you don’t necessarily need to see the same car. As a result, pictures of different but identical cars will pop up before your eyes in the same position, which means the picture will seem to stop. The main thing is to synchronize the opening of the window with the speed of the train, so that the position of the car does not change when opening. If the speed does not match, the cars will “move” either forward or backward at a speed depending on the degree of desynchronization.
Built on the same principle strobe- a device that allows you to look at fast moving or rotating crap. There, too, the curtain opens and closes quickly.
So, An oscilloscope is the same strobe, only electronic. And it doesn’t show cars, but periodic voltage changes. For the same sinusoid, for example, each subsequent period is similar to the previous one, so why not “stop” it, showing one period at one time.
Design
This is done through ray tube, deflection system and scan generator.
In the beam tube, a beam of electrons hitting the screen causes the phosphor to glow, and the plates of the deflection system allow this beam to be driven across the entire surface of the screen. The higher the voltage applied to the electrodes, the more the beam is deflected. Feeding onto plates X sawtooth voltage we create a scan. That is, our beam moves from left to right, and then sharply returns and continues again. And on the plates Y we apply the voltage being studied.
Principle of operation
Then everything is simple, if the beginning of the appearance of the saw period (the beam is in the extreme left position) and the beginning of the signal period coincide, then in one scanning pass one or more periods of the measured signal will be drawn and the picture will seem to stop. By changing the sweep speed, you can ensure that only one period remains on the screen - that is, during one period of the saw, one period of the measured signal will pass.
Synchronization
You can synchronize the saw with the signal either manually, adjusting the speed with the handle so that the sine wave stops and possible by level. That is, we indicate at what input voltage level we need to start the sweep generator. As soon as the input voltage exceeds the level, the sweep generator will immediately start and give us a pulse.
As a result, the scan generator produces a saw only when needed. In this case, synchronization is completely automatic. When choosing a level, you should take into account such a factor as interference. So if you take the level too low, then small needles of interference can start the generator when it is not needed, and if you take the level too high, then the signal can pass under it and nothing will happen. But here it’s easier to turn the knob yourself and everything will immediately become clear.
The synchronization signal can also be supplied from an external source. 
The theory is out of the way, let's move on to practice.
I will show you the example of my oscilloscope, stolen a long time ago from the defense enterprise Design Bureau "Rotor" :). An ordinary oscil, not very sophisticated, but reliable and simple as a sledgehammer.
So:
Brightness, focus and illumination of the scale are, I think, self-explanatory. These are the interface settings.
Amplifier U and up and down arrows. This knob allows you to move the signal image up or down. Adding additional offset to it. For what? Yes, sometimes the screen size is not enough to accommodate the entire signal. We have to drive it down, taking the lower limit, rather than the middle, as zero.
Below goes toggle switch switching input from direct to capacitive. This toggle switch in one form or another is found on all oscilloscopes without exception.
Important thing! Allows you to connect the signal to an amplifier either directly or through a capacitor. If you connect directly, it will work both constant component and variable. And it goes through the conduit variable only.
For example, we need to look at the noise level of the computer's power supply. The voltage there is 12 volts, and the amount of interference can be no more than 0.3 volts. Against the background of 12 volts, these measly 0.3 volts will be completely unnoticeable. You can, of course, increase the gain by Y, but then the graph will go off the screen, and the offsets along Y not enough to see the top. Then we only need to turn on the capacitor and then those 12 volts of constant voltage will settle on it, and only the alternating signal will pass into the oscilloscope, those same 0.3 volts of interference. Which can be enhanced and seen in full height.
Next comes the coaxial connector for connecting the probe. Each probe contains signal and ground. The ground is usually placed on the negative or on the common wire of the circuit, and the signal wire is poked according to the circuit. The oscilloscope shows the voltage on the probe relative to the common wire. To understand where the signal is and where the ground is, just grab them with your hand one by one. If you take the general one, then the corpse’s pulse will still be on the screen. And if you take up the signal signal, you will see a bunch of crap on the screen - interference to your body, which is currently serving as an antenna. On some probes, especially modern oscilloscopes, Built-in voltage divider 1:10 or 1:100, which allows you to plug the oscilloscope into an outlet without the risk of burning it. It turns on and off with a toggle switch on the probe.
Still on almost every oscilloscope there is a calibration output. Where you can always find rectangular signal with a frequency of 1 KHz and a voltage of about half a volt. Depending on the oscillator model. It is used to check the operation of the oscilloscope itself, and sometimes it comes in handy for testing purposes :)
Two hefty knobs: Gain and Duration
Gain serves to scale the signal along the axis Y. It also shows how many volts per division it will ultimately show.
Let's say, if you have 2 volts per division, and the signal on the screen reaches a height of two cells of the dimensional grid, then the amplitude of the signal is 4 volts.
Duration determines the sweep frequency. The shorter the interval, the higher the frequency, the more high-frequency signal you can see. Here the cells are already graduated in milli and microseconds. So by the width of the signal you can calculate how many cells it is, and by multiplying it by the scale along the axis X You will get the duration of the signal in seconds. You can also calculate the duration of one period, and knowing the duration it is easy to find the frequency of the signal f=1/t
Twisted top allows you to change the scale smoothly. I usually have it on a click so that I always clearly know what scale I have.
There is also input X to which you can send your signal, instead of a sweep saw. Thus, an oscilloscope can serve as a TV or monitor if you assemble a circuit that will form an image.
Twist with the inscription Scan and the left and right arrows allow you to move the graph left and right across the screen. It is sometimes convenient to adjust the desired area to the divisions of the grid.
Synchronization block.
Level knob— sets the level from which the saw generator will start.
Switch from internal to external, allows you to apply clock pulses to the input from an external source.
Switch labeled +/- switches level polarity. Not available on all oscilloscopes.
Handle stability— allows you to manually try to select the synchronization speed.
Fast start.
So, you turned on the oscil. The first thing you need to do is to short-circuit the signal probe to your own earthenware crocodile. In this case, “Corpse Pulse” should appear on the screen. If it doesn’t appear, then turn the stabilization and offset and level knobs - maybe it just hid behind the screen or didn’t start due to insufficient level.
As soon as the band appears, use the offset knobs to set it to zero. If you have an analog oscill, especially if it’s an ancient one, then let it warm up. After turning it on, mine floats for another fifteen minutes.
Set it further voltage measurement limit. Take extra if you need to reduce anything. Now, if you attach the ground wire of the oscilloscope to the minus of the battery, and the signal wire to the plus, you will see how the graph jumps by one and a half volts. By the way, old oscilloscopes often begin to falsify, so using a reference voltage source is useful to see how accurately it displays the voltage.
Choosing an oscilloscope.
If you've just started, then anyone will suit you. Extremely preferably if he will two-channel. That is, it will have two probes and two Gain knobs, for the first and second channel, which allows you to simultaneously obtain two graphs.
The second most important criterion for an oscilloscope is frequency. The maximum frequency of the signal that it can pick up. 1MHz was enough for me so far I didn’t aim for more. Those oscilloscopes that are sold in stores already have a frequency of 10 MHz and higher. The cheapest oscilloscope I saw cost 5 thousand rubles - . A two-channel one already costs 10 thousand, but I set my sights and got it for a kilobuck. Different requests - different toys. But, I repeat, 1 MHz is enough for a start, and will last for a long time. So find yourself at least some kind of oscilloscope. And then you will understand what you need.
"We got acquainted with the basics of the operation of this wonderful device. To master working with an oscilloscope, you need practical exercises. The article discusses simple experiments with a power supply based on a transformer, with a bridge rectifier, as well as with RC circuits. The material will be useful for those who want to get acquainted with a measuring device-oscilloscope.
Let's start with the simplest thing - with a power supply on a power transformer and a bridge rectifier. First of all, you need a transformer, let it be a Chinese “ALG” with a secondary winding of 12V (Fig. 1). We will connect the input of an oscilloscope (let it be C1-65) and a multimeter to the secondary winding of the transformer.
Pre-knob the oscilloscope “Time/div.” set to “10”, and the “V/div” knob. also to “10”, and set the input switch to the “pulse mode” position. Now let’s apply 220V alternating voltage to the primary winding (from the mains, observing all the necessary electrical safety rules).
Rice. 1. Scheme for the experiment and image on the oscilloscope screen.
Now let's compare the readings of an oscilloscope and a multimeter. The multimeter will show an alternating voltage of 12V (or so), and the peak-to-peak sine wave on the oscilloscope screen will be as much as 34V. Knowing that the amplitude value of the sinusoidal voltage is equal to half the peak-to-peak, and the effective value is root_of_2 times less than the amplitude, we calculate the effective value:
Let's connect a bridge rectifier consisting of four diodes to the secondary winding of the transformer (Fig. 2). Let's connect an oscilloscope to the output of the rectifier.
There will be a very interesting picture on his screen - the lower half-waves of the sinusoid seem to have turned over and are located along the positive Y axis. In fact, the frequency of oscillations has doubled, that is, no longer 50, but 100 Hz, and the swing has decreased by half.
What is visible on the screen (Fig. 2) is usually called pulsating voltage. But pulsating voltage is not suitable for powering an electronic circuit - it is not yet a constant voltage.
And to make it constant, you need to smooth out the pulsations using a storage capacitor.
Figure 3 shows a circuit with storage capacitor C1 and resistor R1, which serves as a load. Let's see what the instruments show us now. The multimeter will show something around 16.5V, and on the oscilloscope screen you will see a curved line raised up the Y scale by a certain amount (Figure 3, left oscillogram).
Rice. 2. Connect and examine a bridge rectifier consisting of four diodes.
At the upper peaks of the curvature of this line - at 17V. This is what voltage looks like with smoothed ripples. To see the amount of ripple, you need to switch the oscilloscope input to alternating current “~” and turn the “V/div.” knob. downward until the pulsations are clearly visible. In this case, set to 0.5V/div. (Fig. 3, oscillogram on the right). It can be seen that the pulsation range is 1V.
Thus, at the output of our rectifier there is a constant voltage with 1V ripple. The magnitude of these ripples depends on the capacity of the smoothing capacitor and the load. If the load increases (resistance R1 decreases), the ripples will increase.
Rice. 3. Smoothing capacitor in the rectifier.
This can be verified by replacing R1 with a variable. And as the capacitance increases, the ripples decrease. Now, if in the same example (with the same resistance R1) you connect another capacitor with a capacity of 220 µF in parallel with C1, the ripple will decrease to 0.3V, and with a capacitor capacity of 1000 µF the ripple level will be less than 0.1V.
But this is with a load resistance of 1 kOhm, that is, with a load current of 16 milliamps. As the load current increases, the ripple will increase. This is why in rectifiers designed for heavy loads, smoothing capacitors of very large capacity are used.
Above, using an oscilloscope, the operation of a bridge rectifier was examined. But the power supply, often, in addition to the transformer and rectifier, contains a voltage stabilizer.
The circuit of the simplest parametric stabilizer consists of a zener diode and a current-limiting resistor. The main property of a zener diode is that it seems to work like a diode, that is, it passes current in the forward direction, but it also passes reverse current, but only if the reverse voltage exceeds a certain value - the stabilization voltage.
Let's connect the parametric stabilizer circuit to the secondary winding of the transformer, and using an oscilloscope, let's see what the alternating voltage sinusoid has turned into (Fig. 4). Time/div knob Set the oscilloscope to “10” and the “V/div” knob. also on “10”, and the input switch is in pulse mode.
Rice. 4. Let's explore the parametric stabilizer.
The zener diode, working as a diode half-wave rectifier, removed the negative half-waves. And as a zener diode, it cut off the top of the positive half-waves at the level of its stabilization voltage (for D814V it is 10V).
Now, let’s connect the same stabilizer at the output of the rectifier bridge (Fig. 5). The zener diode also cut off the pulsating voltage pulses at the level of its stabilization voltage. Moreover, the zener diode does not care what amplitude these pulses or half-waves are, 17V or, for example, 27V, it will limit them STABLE at the level of 10V.
Rice. 5. We examine the parametric stabilizer at the bridge output.
Figure 6 shows the circuit of a power supply with a parametric regulator at the output. A multimeter and oscilloscope will show a constant voltage of 10V, and the ripple will be significantly less than without a stabilizer.
Rice. 6. Circuit of a power supply with a parametric stabilizer at the output.
Another practical oscilloscope exercise would be to examine an RC circuit using an oscilloscope. For this we need a square pulse generator. Many oscilloscopes, in particular the C1-65, have a calibrator. This is a constant voltage or rectangular pulse generator with a frequency of 1 kHz.
The calibrator is intended for calibration, but it can be successfully used as a laboratory generator of rectangular pulses when setting up and repairing equipment.
But, there are oscilloscopes without calibrators, if yours is like this, then you will need to take a laboratory function generator or make a simple square wave generator yourself with a frequency of about 1 kHz, according to the circuit shown in Figure 1. This is the simplest multivibrator on a digital chip. But for our experiments it is suitable.
Next, we will consider working with an oscilloscope calibrator as a pulse source. If the pulses are taken from a separate generator (for example, as in Fig. 1), you will simply need to supply them to the RC circuit under study from it. At the same time, do not forget to connect the general minus of the generator power supply to the “housing” terminal of the oscilloscope.
Rice. 1. Circuit of a simple pulse generator.
And so, if we connect the “U” and “Calibrator Output” sockets with a piece of wire, we turn on the calibrator to generate pulses with a swing of 5V. In this case, set the “V/div” knob to “1”, and set the “time/div” knob to “0.2mS”, switch the input to alternating voltage “~”, approximately what is shown in Figure 2 will be visible on the oscilloscope screen. That is, rectangular pulses.
Rice. 2. Pulses on the oscilloscope screen.
To experiment with an RC circuit, you will need a 0.01 µF capacitor (often referred to as “10p” or “103”) and a 100 kOhm variable resistor.
We will experiment with two types of circuits - differentiating and integrating.
First, we connect a differentiating circuit consisting of resistor R1 and capacitor C1 (Fig. 3). Now the impulses
Rice. H. Connect the differentiating circuit.
from the calibrator to the “U” input of the oscilloscope through circuit R1C1. Set resistor R1 to the maximum resistance position. In this case, the pulses on the oscilloscope screen will look like in Fig. 4. Their amplitude will increase slightly, but there will be a slope towards the decline.
Rice. 4. Pulses on the oscilloscope screen.
If you start turning the handle of the variable resistor R1, its resistance will decrease, and at the same time, the amplitude of the pulses will increase, but the slope towards the decline also increases. In Figure 5 it doesn’t look at all like rectangular pulses. However, the amplitude of the peaks increased significantly. With further rotation of R1, the amplitude of the peaks will continue to increase, and the slopes will take on a parabolic shape.
Rice. 5. It no longer looks like rectangular pulses.
But, with further rotation of R1, the amplitude begins to decrease, and in the most extreme position, when the resistance of R1 is zero, the pulses disappear (this is not surprising, because R1, in a state of zero resistance, actually shorted the input of the oscilloscope).
The conclusion is that as a result of differentiation of a rectangular pulse, it turns into a pointed pulse of increased amplitude. Moreover, the larger R1, the more similar the pulse is to rectangular.
This is due to the fact that the charging and discharging time of the capacitor depends on the resistance R1. And the smaller R1, the shorter this time. In addition, when moving from a positive half-wave to a negative one (and vice versa), the voltage accumulated on the capacitor is added to the pulse amplitude.
Therefore, the voltage amplitude across resistor R1 in peaks increases the more, the faster the capacitor charges. But the smaller the R1, the narrower the peaks. Now let's swap the parts to get the circuit shown in Figure 6. The RC circuit has become integrating.
Rice. 6. New scheme for the experiment.
If the variable resistor R1 is in the position of minimum resistance, the oscilloscope screen will look like in Fig. 7. Almost the same rectangular pulses, only the rises and falls are slightly smoothed.
We begin to turn the knob of the variable resistor R1, - the rises and falls are smoothed out even more and take on the appearance as in Figure 8. At the same time, the amplitude decreases significantly.
We unscrew the handle of the variable resistor R1 to the end (to the position of maximum resistance), - the amplitude of the pulses decreases greatly, and they already resemble triangles (Fig. 9).
Rice. 7. Image on the oscilloscope screen for the experiment.
In the integrating circuit, the oscilloscope shows the voltage across the capacitor. Pulses are sent to it through resistor R1 and charge and discharge it. As in the first case, the lower the resistor resistance, the higher the charge-discharge rate. But here the situation is the opposite, therefore, the smaller R1, the sooner C1 is charged or discharged to the maximum or minimum value.
This means that the steeper the fronts and declines of the pulses on C1. These are the roundings visible on the oscillogram in Fig. 7 is the very time during which the capacitor is charged and discharged.
And the faster the capacitor charges, the smaller these areas are. The speed of charging the capacitor depends on the resistance of resistor R1, through which pulses are sent to it.
As the resistance of resistor R1 increases, the capacitor charges and discharges more and more slowly and smoothly, and the curves indicating the charging and discharging time increase. Therefore, fronts and recessions smooth out and become inclined.
With a further increase in resistance R1, the time required to charge the capacitor to the maximum voltage increases by so much that it becomes longer than the duration of the half-cycle of the pulse. The capacitor simply does not have time to charge to its maximum value before it begins to discharge.
Rice. 8. Fronts and recessions are even more smoothed out.
Rice. 9. Pulses - triangles on the oscilloscope screen.
Therefore, the pulse amplitude decreases by as much as the capacitor does not have time to charge. Ultimately, the shape of the pulses becomes more and more triangular.
Any electrical laboratory must be equipped with measuring equipment to determine signal sources, voltage levels, current strength, and so on. This allows you to carry out not only the necessary research, but also the design or construction of various instruments and devices. In an industrial enterprise, especially where high-frequency currents are present, it is almost impossible to do without an oscilloscope (the main instrument for measuring electricity).
This device allows you to visualize voltage on a special screen. It produces an oscillogram, which is a graph of changes in the electric current parameter over a certain period. The main value of an oscilloscope is the ability to simultaneously measure voltage, frequency, current and phase angle. All results are immediately processed and displayed on the screen in the form of a graph that shows the shape of the electrical signal. As a result, the observer can see the processes that occur in the electrical circuit, determine the source of the failure, and turn off the device in a timely manner to prevent damage or disaster.
Typically, DC voltage is an ideal sine wave. However, in practice this is not always the case - the network voltage may fluctuate, which will be reflected on the screen of the device being described. In such a situation, it is almost impossible to accurately measure this parameter using a standard voltmeter (there will be significant errors: measuring equipment with arrows will give some values, digital devices will give others, and devices for measuring DC voltage will give others). The only way to accurately determine the voltage in such a network is to use an oscilloscope.
These measuring devices make it possible not only to monitor the signal shape in real time, but also to save the obtained information, which can then be processed on computers when studying and modeling various processes. The oscillogram that the described device displays on the screen provides the opportunity to observe the following features of the measured signal:
Most often, oscilloscopes are used to study signals that are periodic in nature.
The key element of the device is a cathode ray tube (CRT). Air is pumped out of it so that a vacuum is formed inside, in which the cathode (a positively charged substance) is located. When exposed to electric current, it begins to emit negatively charged particles, which are then focused using a special system and directed to the inner surface of the screen. This surface is coated with a special substance - a phosphor, which produces a glow when hit by a beam of electrons. As a result, if you look at the device from the outside, you can observe the movement of a luminous point on the screen.
Focusing and directing the beam in a CRT is carried out using two pairs of plates that control the movement of electrons in two planes. In horizontal mode, the electron beam deviates in proportion to the change in time, and in vertical mode, it deviates in proportion to the measured voltage.
When observing the nature of the signal using an oscilloscope, the voltage should be applied to the vertical plates. The resulting graph of the parameter change, as a rule, has the shape of a saw: first, the potential difference increases in a linear relationship, and then a sharp decline follows. In addition, by observing the movement of the beam on the screen, you can see its deflection to the left or right. This indicates the sign of the voltage: when it is negative, it moves to the left, and when it is positive, it moves to the right. Most often, the beam moves from left to right at a constant speed.
This movement of a point on the device screen is called scanning. The horizontal line drawn by the beam is called the zero line. Time measurements are made relative to it. Sweep frequency refers to the frequency with which sawtooth pulses are repeated.
Since voltage is a potential difference, it should be measured at two points. For this purpose, the oscilloscope is equipped with two terminals that supply voltage to the plates. The first terminal is the input and is connected to the signal source, which leads to the vertical deflection of the beam. The second is called the common wire and is grounded (closed to the body of the device itself).
In order to correctly connect the device, you need to know in advance which of the wires is a phase (which wire carries the electric current). In foreign devices, there are special probes for this purpose, which allow you to determine the presence of voltage at the input and which terminal to connect to which source. In this case, the common wire ends with an alligator clip, which makes it easy to attach it to the metal body of the measuring device. The terminal that makes contact with the phase is shaped like a needle, making it easy to measure the electrical signal anywhere: a socket, a wire, a printed circuit board, or even on a microprocessor chip leg.
Once the terminals are installed, you can proceed directly to measurements. In almost any electrical circuit there is a single wire, and to check the parameters it is recommended to measure the signal characteristics on it. But this situation may not always be the case. Then you should select the points where measurements are required and carry them out (most often, the places of the most likely malfunction are chosen as such points).
Note! The main task of an oscilloscope is to monitor voltage dynamics. But by connecting a resistance, you can also examine the shape of the electrical current signal. The resistance value in this case should be significantly lower than the total resistance of the circuit under study. Only if this condition is met will the measurements be correct, since the device will not affect the functioning of the circuit.
The standards for organizing electrical circuits in the Russian Federation differ from foreign ones, so the measuring equipment has to be connected differently. In particular, plugs with a probe diameter of 4 millimeters are used. Since they are the same, in order to connect the device correctly, you need to pay attention to the following signs:
Important! However, such designations are not always found. The devices may have been repaired, the plugs may have been replaced, so to determine which wire has phase and which wire has zero, it is recommended to use a proven method. To do this, you need to touch one plug with your hand first, and then the other. If the user touches the plug on the negative wire, a horizontal line will appear on the screen. When you touch the phase wire, a sine wave with a lot of noise (interference) will be displayed on the screen. This method is error-free, and interference appears due to the influence of other electrical appliances located in the room.
A special feature of this device is the ability to simultaneously display signals from two different sources on the screen. This type of measuring apparatus has two channels, marked accordingly. In this case, the terminals of the neutral wire of both channels are connected to the housing, therefore, when measuring pulses with such a device, you should not allow them to be connected to different places in the same electrical circuit, since in this case a short circuit may occur and the voltage information will be incorrect.
The only drawback of a dual-channel oscilloscope is the inability to observe two different voltages simultaneously. However, this problem is not critical, since in most cases the neutral wire is connected to the housing and is common to two phases, which means that voltage measurement is carried out using this conductor.
The advantage of such a device is the ability to control two parameters of the electrical circuit: current and voltage. To measure current, it is necessary to include in the circuit an additional resistance with certain parameters (it should not exceed the total resistance of the circuit so as not to create measurement errors). Using such an oscilloscope is quite a complex task, so it is recommended to always have reference books and diagrams for its correct connection.
Additional Information. The design feature of a two-channel oscilloscope should also be taken into account. It has some asymmetry: the synchronization of the first channel has higher quality and stability compared to the second. Therefore, to obtain a correct oscillogram, it is recommended to use the first channel to monitor the voltage, and the second – to monitor the current.
To monitor this signal characteristic using an oscilloscope, you should focus on the values of the vertical scale of the screen. To obtain the values, you need to connect the terminals of the device to each other, and then turn on the measurement mode. After this, you need to adjust the device so that the scan line is aligned with the central horizontal line on the screen.
Only after completing the described preparatory steps can the device be switched to measurement mode. To do this, the input terminal should be placed on the signal source that you want to study.
Important! Taking measurements using a portable oscilloscope is somewhat more difficult, since it has a significantly larger number of settings and adjustments, so it is recommended to use it either if you have the appropriate experience, or by checking each action with the instructions.
After a signal is sent to the input of the device, a graph will appear on the screen. To measure the height of the sine wave (voltage level), it is also necessary to make an adjustment: install the plates so that the point on the screen is on a vertical line. This way it will be much easier to take measurements, since there is a scale with values on it.
The oscilloscope also allows you to measure signal periods. To calculate the frequency in the future, you can use a simple formula, since the frequency is inversely proportional to the signal period (increasing the period leads to a reduction in frequency and vice versa).
It is easiest to measure the period in places where the waveform intersects the horizontal axis. Therefore, to obtain correct values, it is recommended to adjust the scan line before starting the study in the same way as when monitoring voltage.
After this, you need to set the point to start moving on the leftmost line on the screen. Next, you only need to fix the value at which the point intersects the horizontal line. Having calculated the value of the period, you can use a special formula to determine the frequency. To increase the accuracy of measurements, you should stretch the graph as much as possible in the horizontal plane. Optimal accuracy is considered to be an error of less than one percent, but such parameters can only be obtained on digital devices with linear scanning.
This phenomenon demonstrates the relative position of the graphs of two electrical signals over a certain period of time. The magnitude of the shift is measured in parts of a period (degrees), rather than in units of time. This is explained by the peculiarity of the graph, which in its shape represents a sinusoid, which means that the difference in the graphs depends on the difference in the magnitude of the angles.
Maximum accuracy can also be obtained by stretching the graph in length. Due to the fact that each signal is displayed with the same brightness and color, it is recommended to set them to different amplitudes. To do this, the maximum possible voltage should be applied to the first channel, which will improve the synchronization of the image on the screen.
Thus, using an oscilloscope requires certain skills and theoretical knowledge, but the measurements of electrical signal parameters that this device allows you to detect various faults, as well as design high-quality new products.
This note will be gradually updated with simple but useful techniques for working with an oscilloscope.
The main question to answer is: "What can you measure with an oscilloscope?" As you already know, this device is needed to study signals in electrical circuits. Their shapes, amplitudes, frequencies. Based on the data obtained, we can draw conclusions about other parameters of the circuit under study. This means that with the help of an oscilloscope you can basically (I’m not talking about the super functions of super-modern devices):
All further examples should be done with an analog oscilloscope in mind. For digital everything is the same, but it can do more than analog and in certain matters eliminates the need to think where you can simply show a number. A good tool should be like that.
So, before work, you should prepare the device: put it on the table, connect it to the network =) Oh well, I’m just kidding. But if possible, it should be grounded. If there is a built-in calibrator, then according to the instructions for the device you need to calibrate it. (hint: instructions are online).
You will connect your oscilloscope to the circuit under study using a probe. This is a coaxial wire, at one end of which there is a connector for connecting to an oscilloscope, and at the other end there is a probe and ground for connection to the circuit under study. Any random wire cannot be used as a probe. Only special probes. Otherwise, instead of the real picture of things, you will see nonsense.
I will not look at each oscilloscope control in detail. There are a lot of such reviews on the Internet. Let's better learn how to carry out amateur measurements: we will determine the amplitude, frequency and period of the signal, shape, amplifier bandwidth, filter cutoff frequency, power supply ripple level, etc. Other tricks and tricks will come with practice. You will need an oscilloscope and a signal generator.
I will speak without lordly tricks, like a peasant. On the oscilloscope screen you will see either a sinusoidal signal, or a saw, or rectangles, or a triangular signal, or just some nameless graph.
There are countless types of signals. And the signals themselves do not know that they belong to some species. So your task is not to remember the names, but to look at the screen and quickly figure out what you see on it means, what process is going on in the circuit.
The oscilloscope can measure both DC and AC voltage. All devices have two modes for this: measuring only an alternating signal, measuring a constant and alternating signal simultaneously.
This means that if you choose to measure an alternating signal and connect the probe to a battery, then nothing will change on the device screen. And if you choose the second mode and do the same thing, then the line on the device screen will shift upward by approximately 1.6V (the value of the emf of a finger-type battery). Why is this necessary? To separate the DC and AC components of the signal!
Example. You have decided to measure the ripple in a newly assembled 30V DC voltage source. You connect it to an oscilloscope, and the beam runs far up. In order to conveniently observe the signal, you will have to select the maximum value of V/div per cell. But then you definitely won’t see the pulsations. They are too small. What to do? Switch the input mode to measure alternating voltage and turn the V/Div knob to a much smaller scale. The DC component of the signal will not pass through and only the ripples of the power source will be shown on the screen.
It is easy to determine the amplitude of the alternating voltage by knowing the value of the V/div division and simply count the number of cells along the ordinate axis that this signal occupies from the zero value (average) to the maximum.
If you look at the oscilloscope screen in the picture above and assume that V/div = 1V, then the amplitude of the sine wave will be 1.3V.
And if we assume that Time/div (sweep) is set to 1 millisecond, then the period of this sine wave will occupy 4 cells, and the period T = 4 ms will be read. Easily? Let's now calculate the frequency of this sine wave. Frequency and period are related by the formula: F = 1/T (T in seconds). Therefore F = 1/ (4*10 -3) and equals 250 Hz.
Of course, this is a very rough estimate, which is only suitable for such clean and beautiful signals. And if you submit some kind of musical composition instead of a pure sine wave, then it will contain many different frequencies and you can’t guess by eye. To determine which frequencies are included in this composition, you will need a spectrum analyzer. And this is a different device.
As I wrote above, you can also measure frequency using an oscilloscope. You can also not only measure the frequency of a sinusoidal signal, but even compare the frequencies of two signals, for example, using Lissajous figures.
This is very convenient when you want, for example, to calibrate a signal generator you’ve assembled yourself, but don’t have a frequency counter at hand. This is when Lissajous figures come to the rescue. It's a pity not all analog oscilloscopes can show them.
It often happens that the current phase and voltage phase diverge. For example, after passing through a capacitor, inductor or whole circuit. And if you have a two-channel oscilloscope, then you can easily see how much the phases of current and voltage differ (And if you have a modern digital one, then there is even a special function for measuring the phase shift. Cool!). To do this, connect the oscilloscope like this:
