The article will describe in detail how to use the oscilloscope, what it is and for what purpose it is needed. No laboratory can exist without measuring equipment or sources of signals, voltages and currents. And if you plan to engage in the design and creation of various devices (especially when it comes to high-frequency technology, for example, inverter power supplies), then without an oscilloscope to do something will be problematic.
What is an oscilloscope?
This is such a device that allows you to "see" the voltage, or more precisely, its shape over a certain period of time. With it, you can measure many parameters - voltage, frequency, current strength, phase angle. But what is especially good about this device is that it allows you to visually evaluate the waveform. Indeed, in most cases, it is she who talks about what exactly is happening in the chain 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 may be far from the ideal sinusoid. Voltmeters, for example, perceive such a signal with large errors. Dial gauges will produce one value, digital gauges will produce much less, and DC voltmeters will be several times larger. The most accurate measurement is obtained using the instrument described in the article. And it does not matter whether the H3013 oscilloscope is used (how to use it, discussed below) or another model. Measurements are the same.
Instrument Features
Digital oscilloscopes can not only show in real time the waveform, but also save all the data that can later be read on personal computers. From the waveform shown in the figure above, you can determine some features of the signals:
- The nature of the signal is pulsed.
- Negative values have no input signal.
- A very rapid change occurs between 0 and maximum and vice versa.
- The pulse duration is more than three times the duration of the pause.
As a rule, with the help of an oscilloscope, periodic signals are studied. It is about them that the article will be discussed.
How does it work
The heart of all oscilloscopes is the cathode ray tube. This, one might say, is a radio lamp, therefore, there is a vacuum inside. Electron emission occurs at the cathode. Using a focusing system, a thin beam is formed from these electrons. The inside of the screen is covered with an even layer of phosphor. When exposed to electrons, it begins to glow. Looking outside the screen, you can see a bright spot in the middle.
There are two pairs of plates in the cathode ray tube that direct the electron beam in the desired direction. Moreover, its deviation occurs in perpendicular (mutually) directions. Simply put, we get two coordinate systems. To monitor the voltage on the handset screen, you need to:
- The beam should be deflected horizontally so that the deviation is directly proportional to time.
- In the vertical plane, it is necessary that the deviation value be proportional to the voltage that is being studied.
Scan
The sweep voltage must be applied to those plates that are located in a vertical plane. It is sawtooth, slowly growing linearly, and it has a very fast decline. In this case, a positive voltage causes the beam to deviate to the right. And 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 moves from left to right. Moreover, its speed is constant. After reaching the extreme right border, he quickly goes to the original. Then the movement repeats.
This article will tell you as much as possible about how to use the oscilloscope correctly. The above process is called “sweep”. A scan line is a line (horizontal) drawn by a beam on the screen. When measurements are taken, it is called the zero line. She is the axis of time on the chart. The sweep frequency is nothing but the frequency with which the repetition of sawtooth pulses occurs. In the measurement process, it is not applied. Important parameters for measurements are speed.
How to connect an imported oscilloscope
The voltage must be measured at two points, which means that the input of the oscilloscope is two terminals. Please note that the functions of each terminal are different:
- The first is connected to the input of the amplifier, which deflects the beam in a vertical plane.
- The second terminal is a common wire (ground, minus, housing). It has an electrical connection directly with the device body.
From this we can conclude that with the help of an oscilloscope, the phase voltage relative to the ground is measured. And you need to know which of the inputs is the phase. In devices of foreign manufacture, special probes are 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 the measurements are taken. But the phase is in the form of a needle. With its help, you can easily poke at any place in a printed circuit, even into a single leg of a microprocessor.
How to connect a domestic oscilloscope
In Russia, different standards, therefore, on domestic devices everything is different. The most commonly used plugs are 4 mm in diameter. Moreover, they are the same, you have to find out some signs in order not to confuse the connection:
- The negative output, as a rule, has a large length.
- Black or brown is characteristic of a ground wire.
- On the earthen plug are applied UGO "grounding" or "common wire".
But this can not always be found, since the cables are often subjected to repair, during which the available plug is installed on the wire. With a 100% probability, you can determine which wire is zero and which is phase, in one way. First, touch one plug with your hand, then the other. And it doesn’t depend on the model, it doesn’t matter if it is a C1-118A oscilloscope (how to use the devices will be described below) or some other.
In that case, if you hold the negative cable in your hand, you can observe a flat horizontal line on the device’s screen. And if you touch the phase wire, a distorted sine wave with a huge amount of interference will appear on the screen. The latter are observed due to the fact that there is some capacity between the wires of the household electrical network in the room and your body (the space in the room is a dielectric).
Further actions
When phase and minus are determined, measurements can be taken. In the event that you cannot visually determine the common wire for all elements, you must connect to the points between which you need to measure the voltage. But most often in the circuit there is a common wire, it can even be connected to ground. The OMSh-2M oscilloscope is prepared in the same way. How to use it to measure quantities will be described below. In this case, the ground wire of the oscilloscope must be connected to it.
In essence, an oscilloscope is a voltmeter that shows a graph of voltage changes over a specific time span. But it allows you to see the shape of the electric current. To do this, you need to connect a special current resistance. Moreover, its value should be less than the total resistance of the circuit itself. In this case, the resistor will not be able to influence the operation of the circuit.
Dual Channel Oscilloscope
It is also called double-beam, it has one feature - it can output signals from two different sources on the screen at the same time. It has two channels, which are indicated by Roman numerals. Please note that in both channels the negative terminals are electrically connected to the housing. Therefore, when taking measurements, do not allow these wires to be connected to different parts of the circuit. Here's how to use the C1-68 oscilloscope, for example, to measure current and voltage at the same time.
In addition, there is a risk of receiving incorrect information, since the circuit changes dramatically due to this short circuit. The disadvantage is the inability to observe two different voltages. But it is not very significant, since in most devices one of the poles (as a rule, the negative output of the power source) is connected to the body, and it is common. Therefore, measurements of all voltages occur relative to this common wire.
Dual Channel Features
Using a two-channel oscilloscope, you get the ability to control the current and voltage in the circuit at the same time. Therefore, easily measure the phase shift between voltage and current. One channel should measure the current, and the second - the voltage in the circuit under study. To measure the current, as you remember, it is necessary to include in the circuit some resistor with a certain resistance. Since it is quite difficult to use the C1-94 oscilloscope and its analogs, you need to keep the recommended connection schemes to measure this or that parameter handy.
It is worth paying attention to the design of oscilloscopes - it is a little asymmetrical. In other words, the synchronization of the first channel is much better and more stable than the second. Therefore, you need to connect the findings of the first channel to measure voltage, not current. This will provide a more stable display of the waveform on the screen of the device. Never connect the negative terminals of two channels to different points on the circuit! Always connect them together.
Governing bodies
On the front panel of the device there are several handles that are necessary for fine-tuning the oscilloscope. Two potentiometers - to control channels 1 and 2. There is also a function for controlling synchronization, sweep, there is the ability to adjust focus, brightness, backlight. If you look closely at the screen, you can see that it is divided into small squares - divisions. They must be used when taking measurements. It is to these squares that the horizontal and vertical scales should be tied. Such features are the oscilloscope C1-67. How to use instruments 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. Typically, an oscilloscope has approximately 6-10 squares in the horizontal plane and 4-8 in the vertical. Risks are plotted on the center lines, they divide each segment into 10 parts (equal) or by 5. Thanks to these divisions, more accurate calculations can be made.
Login mode
On the front panel there is a special switch that puts the device in various states. It is indicated by a symbol - a straight line is above, a wavy line below it. When moving to the upper position, both alternating and constant voltage can be input. An open input is considered for direct current. When switching to the lower position, only AC voltage is allowed to be input. This makes it possible to measure a very small AC voltage (with respect to very large DC values). Actual for measurements in amplification stages.
To implement this is quite simple - you need to connect a capacitor to the input of the amplifier. In this case, the entrance is closed. Please note that in this measurement mode, the low frequency signals with a frequency of less than 5 Hz are weakened. 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 establish a scan. Since it is impossible to use the C1-49 oscilloscope and analogs without knowledge of the main controls, it is worth talking about them in more detail.
Oscilloscope Channel Input
On the front panel there is a scale in the vertical plane - it is determined using the sensitivity control of the channel through which the measurement takes place. It is possible to change the scale not smoothly, but stepwise, using the switch. What values can be set with it, see the case next to it. On the same axis as this switch is a regulator for smooth adjustment (here's how to use the C1-73 oscilloscope and similar models).
On the front panel you can find the handle with the image of a bidirectional arrow. If you rotate it, then the graph of this channel will begin to move in a vertical plane (down-up). Pay attention to the fact that there is a graphic symbol next to this handle, which shows which side you need to rotate it in order to change the multiplier value to a smaller or larger side. The controls on both channels are the same. In addition, on the front panel there are knobs for adjusting 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 graph display settings.
How are measurements taken?
We continue to describe how to use a digital oscilloscope or analog. It is important to note that they all have a disadvantage. It is worth mentioning one feature - 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 the scan voltages have extremely low linearity, which leads to an error in the measurement of 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 taking measurements of frequency and voltage (there is a time interval), the adjustments for adjusting the signal gain at the input and sweep speed should be set to the extreme right. It is worth noting one feature: since even a beginner can use a digital oscilloscope, devices with a cathode ray tube have lost relevance.
How to measure voltage
To measure the voltage, it is necessary to use scale values in the vertical plane. First you need to do one of these actions:
- Connect both input terminals of the oscilloscope to each other.
- Set the input mode switch to the position corresponding to the connection to the common wire. Then the regulator, near which the bi-directional arrow is depicted, make sure that the scan line coincides with the center (horizontal) line on the screen.
Put the instrument into measurement mode and apply the signal to be examined to the input. At the same time, the mode switch is set to some operating position. But how to use a portable digital oscilloscope? A little more complicated - such devices have much more adjustments.
As a result, you can see some graph on the screen. To accurately measure the height, use the pen with the image of a horizontal bidirectional arrow. Make sure that the top point of the graph falls on a vertical line located in the center. It has a graduation, so it will be much easier to calculate the effective voltage in the circuit.
How to measure frequency
Using an oscilloscope, you can measure time intervals, in particular, the period of the signal. You understand that the frequency of any signal is always proportional to the period. Period measurement can be performed in any area of the waveform. But it is more convenient and more accurate to measure at those points at which the graph intersects with the horizontal axis. Therefore, before starting measurements, 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 analog, the latter have long 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 with the leftmost 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. Measurement accuracy varies. To increase it, you need to stretch the graph horizontally as much as possible.
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The maximum measurement accuracy will be if you stretch the graph to the entire screen length. In analog oscilloscopes, the signal graph for each channel will have one brightness and color. To distinguish these graphs from each other, it is necessary to make for each its own amplitude. And the voltage that is supplied to the first channel is important to make as large as possible. In this case, it will turn out to be much better to keep the image on the screen in sync. Here's how to use the C1-112A oscilloscope. Other devices differ slightly in operation.