How to use the oscilloscope? How to use a portable digital oscilloscope?

The article will tell in detail how to use the oscilloscope, what it is and for what purpose it is needed. No laboratory can survive without measuring equipment or signal sources, 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 without an oscilloscope to do anything will be problematic.

What is an oscilloscope?

This is a device that allows you to "see" the voltage, or more precisely, its shape for a certain period of time. With its help, you can measure a lot of parameters - voltage, frequency, current strength, angles of phase shifts. But what is good especially this device, so this is because it allows you to visually assess the shape of the signal. After all, in most cases it is she who talks about what exactly happens in the circuit in which the measurement is carried out.

In some cases, for example, the voltage may contain not only a constant but also an alternating component. And the shape of the second can be far from the ideal sinusoid. Such a signal voltmeters, for example, are perceived with large errors. Arrow devices will give out one value, digital - much less, and voltmeters of direct current in - several times more. The most accurate measurement is obtained by using the device described in the article. And it does not matter whether the H3013 oscilloscope is used (how to use it, discussed below) or another model. The measurements are the same.

Device Features

Digital oscilloscopes can not only display the waveform in real time, but also save all the data that can later be read on personal computers. According to the oscillogram shown in the figure above, you can determine some features of the signals:

1. The character of the signal is impulse.
2. Negative values do not have an incoming signal.
3. There is a very rapid change in the values from 0 to maximum and back.
4. The pulse duration is longer than the pause duration by more than three times.

Typically, with the help of an oscilloscope, periodic signals are examined. It is about them that will be discussed in the article.

How it works

The heart of all oscilloscopes is a cathode-ray tube. This, it can be said, is a radio lamp, hence, there is a vacuum inside. At the cathode, electrons are emitted. With the help of a focusing system, a thin beam is formed from these electrons. The inside of the screen is covered with an even layer of phosphor. He begins to shine under the influence of electrons. Looking from the outside to the screen, you can see a light point in the middle.

In the cathode-ray tube there are two pairs of plates that direct the electron beam in the desired direction. And its deviation occurs in perpendicular (mutually) directions. In simpler terms, two coordinate systems are obtained. To monitor the voltage on the handset screen, you need:

1. Horizontally, the beam should be deflected in such a way that the deviation value is directly proportional to the time.
2. In the vertical plane, it is necessary that the deviation value is proportional to the voltage, the study of which passes.

Scan

The sweep voltage must be applied to those plates that are located in a vertical plane. It is sawtooth-shaped, slowly increasing linearly, and it has a very rapid decline. In this case, the positive voltage causes the beam to deviate to the right. A negative - to the fact that the beam moves to the left. This is the case if the observer is in front of the screen, and you can see how the beam is moving from left to right. At the same time, its speed is constant. After reaching the extreme right border, he quickly goes to the original one. Then the motion is repeated again.

In this article, we will talk as much as possible about how to use the oscilloscope correctly. The above process is called a "sweep". The sweep line is a line (horizontal) drawn by a beam on the screen. When measurements are taken, it is called the zero line. It is also the time axis in the graph. The sweep frequency is nothing more than the frequency with which the sawtooth pulse repeats itself. In the process of measurement, it is not applied. Important parameters for measurements are the speed.

How to connect an imported oscilloscope

Voltage should be measured at two points, so the input of the oscilloscope is two terminals. Please note that the functions of each terminal are different:

1. The first is connected to the input of the amplifier, which deflects the beam in the vertical plane.
2. The second terminal is a common wire (ground, minus, housing). It has an electrical connection directly to the body of the device.

Hence the conclusion can be drawn that the phase voltage with respect to the earth is measured using an oscilloscope. And it is necessary to know which of the inputs is the phase. In foreign-made devices, a special probe design is used. In them, the common wire is made in the form of a crocodile clip. The most reasonable solution, since it is this wire that most often connects to the metal case of the device on which measurements are taken. But the phase is performed in the form of a needle. With its help, you can easily poke into any place of printed editing, even in a single foot microprocessor.

How to connect a domestic oscilloscope

In Russia, there are other standards, that's why on the devices of domestic production everything is different. The most commonly used plugs are 4 mm in diameter. And they are the same, you have to find out some signs, so as not to confuse the connection:

1. The minus pin, as a rule, has a long length.
2. Black or brown color is typical for earthen wire.
3. The earth plug or the "common wire" are marked on the ground plug.

But this can not always be met, since the cables are often repaired, during which a plug is installed on the wire, which is available. With a probability of 100%, you can determine which wire is zero and which is phase, in one way. First, touch with the hand of one plug, then the other. And it does not depend on the model, it does not matter, it's the C1-118A oscilloscope (how to use the devices, it will be told below), or some other one.

In the event that you keep a negative wire in your hand, you can see a flat horizontal line on the device screen. And if you touch the phase wire, a distorted sinusoid appears on the screen with a huge amount of interference. The latter are observed due to the fact that there is some capacity between the wires of household electricity in the room and your body (the space in the room is a dielectric).

Further actions

When the phase and minus are determined, measurements can be made. In the event that you can not visually determine the common for all elements of the wire, you need to connect to the points between which you want to measure the voltage. But most often there is a common wire in the circuit, it can even be connected to the ground. Oscilloscope OMSH-2M is prepared in the same way. How to use it to measure the quantities will be described below. In this case, the earth wire of the oscilloscope must be connected to it.

In fact, an oscilloscope is a voltmeter that shows a graph of the voltage change at a specific time interval. But it allows us to see the shape of the electric current. To do this, you need to connect a special current resistance. And its value should be less than the impedance of the circuit itself. In this case, the resistor will not affect the operation of the circuit.

Two-Channel Oscilloscope

It is also called double-beam, it has one feature - it can display signals from two different sources on the screen simultaneously. It has two channels, which are denoted by Roman numerals. Please note that in both channels, the negative terminals are electrically connected to the housing. Therefore, do not connect these wires to different parts of the circuit during measurements. Here's how to use the oscilloscope C1-68, for example, for measuring current and voltage simultaneously.

In addition, there is a risk of getting the wrong information, since the chain is drastically changed due to this short circuit. The disadvantage is that it is impossible to observe two different voltages. But it is not very significant, since in most devices one of the poles (usually the negative terminal of the power supply) is connected to the case, and it is common. Consequently, the measurements of all voltages occur relative to this common wire.

Features dual-channel device

Using a two-channel oscilloscope, you get the ability to monitor the current and voltage in the circuit simultaneously. Therefore, easily measure the phase shift between voltage and current. One channel must measure the current, and the second one - the voltage in the investigated circuit. To measure the current, as you remember, it is necessary to include in the circuit some resistor with a certain resistance. Since using the oscilloscope C1-94 and analogs is quite difficult, you need to keep on hand the recommended connection diagrams for measuring a particular parameter.

It is worth paying attention to the design of oscilloscopes - it is a little unsymmetrical. In other words, the synchronization of the first channel is much better and more stable than the second one. Therefore, it is necessary to connect the outputs of the first channel to measure the voltage, and not the current. This will allow a more stable display of the oscillogram on the instrument screen. Never connect the negative terminals of the two channels to different points on the circuit! Always put them together.

Controls

On the front panel of the device there are several handles, which are necessary for accurate adjustment of the oscilloscope. Two potentiometers - for controlling channels 1 and 2. Also there is a function for controlling synchronization, scanning, there is the possibility of adjusting the focus, brightness, backlight. If you look at the screen, you can see that it is divided into small squares - divisions. They must be used for measurements. It is to these squares that the horizontal and vertical scales should be tied. Such features have an oscilloscope C1-67. How to use devices of this type for measuring quantities will be described below.

Note that the horizontal scale is measured in seconds per division. And vertically - in volts per division. As a rule, in an oscilloscope there are approximately 6-10 squares in a horizontal plane and 4-8 in a vertical one. On the center lines, there are risks, they divide each segment into 10 parts (equal) or to 5. Due to these divisions, more accurate calculations can be made.

Login Mode

On the front panel there is a special switch, which switches the device to different states. Denoted by a symbol - on the top a straight line, below it - a wavy one. When transferring to the upper position, both AC and DC voltage can enter the input. The input is open for DC. When switching to the lower position, only the AC voltage input is allowed. Due to this, it becomes possible to measure very small alternating voltages (with respect to very large values of the constant voltage). Actual for measurements in amplifying stages.

To implement this is quite simple - you need to connect the capacitor to the input of the amplifier. In this case, the input is closed. Please note that in this mode, low-frequency signals with a frequency of less than 5 Hz are weakened. Therefore, they can be measured only in the open-entry mode.

When the switch is set to the middle position, the amplifier is disconnected from the input connector and a short circuit to the housing occurs. Due to this, it is possible to set the sweep. Since using the oscilloscope C1-49 and analogs without knowledge of the basic controls is impossible, it is worth talking about them in more detail.

Oscilloscope Channel Input

The front panel has a scale in the vertical plane - it is determined by the sensitivity knob of the channel on which the measurement takes place. It is possible to change the scale not smoothly, but stepwise, with the help of a switch. What values can be set with it, look at the case next to it. On one axis with this switch is a regulator for smooth adjustment (here's how to use the oscilloscope C1-73 and similar models).

On the front panel you can find a handle with the image of a bidirectional arrow. If you rotate it, the graph of this channel will begin to move in the vertical plane (down-up). Note that near this handle there is a graphic symbol that shows which way to rotate it to change the value of the multiplier to a smaller or larger side. The controls of both channels are the same. In addition, on the front panel there are knobs for adjusting the contrast, brightness, synchronization. It is worth noting that the digital pocket oscilloscope (how to use the device, we are considering) also has a number of options for displaying charts.

How measurements are made

We continue to describe how to use a digital oscilloscope or an analog one. It is important to note that they all have a drawback. It is worth mentioning one feature - all measurements are carried out visually, so there is a risk that the error will be high. It should also be taken into account the fact that the sweep voltages have extremely low linearity, which leads to an error in measuring the phase shift or frequency by about 5%. To minimize these errors, one simple condition is required: the graph should occupy approximately 90% of the screen area. When frequency and voltage measurements are carried out (there is a time interval), the gain adjusters for the input signal and the sweep speed should be set to the extreme right positions. It is worth noting one feature: since a digital oscilloscope can be used even by a novice, the instruments with an electron-beam tube have lost relevance.

How to measure stress

To measure the voltage, you must use the scale values in the vertical plane. First you need to do one of these actions:

1. Connect both input terminals of the oscilloscope to each other.
2. Switch the input mode switch to the position that corresponds to the connection to the common wire. Then the regulator, near which the bidirectional arrow is shown, is to ensure that the scanning line coincides with the central (horizontal) line on the screen.

Transfer the instrument to the measurement mode and input the signal to be examined. In this case, a mode switch is installed in any working position. But how to use a portable digital oscilloscope? A bit more complicated - these devices have a lot more adjustments.

As a result, you can see on the screen a certain graph. To accurately measure the height, use the handle with the image of a horizontal bidirectional arrow. You make sure that the top point of the chart falls on a vertical line located in the center. There is a calibration on it, so it will be much easier to calculate the actual voltage in the circuit.

How to measure the frequency

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. The period can be measured in any area of the waveform. But it is more convenient and more accurate to measure at those points where the graph intersects with the horizontal axis. Therefore, before starting the measurement, be sure to set the sweep clearly on a horizontal line located in the center. Since using a portable digital oscilloscope is much easier than analogue, the latter have long since sunk into oblivion and are rarely used for measurements.

Further, using the handle indicated by the horizontal bidirectional arrow, it is necessary to shift the beginning of the period to the extreme left line on the screen. After calculating the signal period, you can use the simple formula to calculate the frequency. To do this, you need to divide the unit into the previously calculated period. The accuracy of the measurements can be different. 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 error value is when it is less than 1 percent. But not every oscilloscope can provide such high accuracy. Only digital, in which linear scanning, you can get such accurate measurements.

How is the phase shift determined?

And now about how to use the oscilloscope C1-112A to measure the phase shift. But for a start - definition. The phase shift is a characteristic that shows how two processes (oscillatory) are arranged relative to each other for some time. And the measurement is not in seconds, but in parts of the period. In other words, a unit of measure is a unit of angle. If the signals are equally located mutually, then the phase shift will also be the same. And it does not depend on the frequency and period - the real scale of the graphs on the horizontal (time) axis can be any.

The maximum measurement accuracy will be if you stretch the graph for the entire length of the screen. In analog oscilloscopes, the waveform for each channel will have the same brightness and color. To distinguish these graphs from each other, it is necessary to make for each its amplitude. And the voltage that is applied to the first channel, it is important to do as much as possible. In this case it will be much better to keep the image on the screen synchronized. Here's how to use the oscilloscope C1-112A. Other devices differ in operation slightly.