Digital phosphor oscilloscopes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

 Comments on the article

The ideal tool for measurements in power circuits

In recent years, there has been a marked increase in the number of design developments that require power measurements in power circuits. Moreover, the very concept of "power measurement" in these circuits has undergone significant changes. The reason for this is the widespread use of switching power supplies, which have become an integral part of most modern electronic devices, including computers, as well as many household appliances.

Until relatively recently, power supply designers were only required to confirm that the blocks they developed provide the required voltage and current at a given ripple level. Today, the tasks of developers have become more complicated. Now the designer is obliged, in particular, to give full information about the power levels and the harmonic composition of the interference generated in the power network by switching power supplies. These parameters of the devices he develops must comply with the requirements of national and international standards for power quality in power networks (for example, the American standard IEEE 519-1992).

In order to competently check the developed devices for compliance with these standards, the designer must be able to measure the output signals of high-speed switching transistors, voltage noise, instantaneous power characteristics, etc. facilities. Such measurements can be greatly simplified by universal oscilloscopes of a new class - digital phosphor oscilloscopes (DPO - Digital Phosphor Oscilloscope).

These instruments provide everything you need to measure power, including real-time display of power changes, advanced triggering capabilities, and an intelligent interface for working with a wide range of probes (passive and active, current, differential). Some DLOs incorporate FFT (Fast Fourier Transform) modules, which greatly simplify the harmonic analysis of the signal.

Better than analog, better than digital...

Since the tasks that arise when studying the characteristics of power supplies have become much more complicated, analog real-time oscilloscopes (RTOS) and digital storage oscilloscopes (DSOs) are no longer effective enough today.

DSOs allow you to analyze the processes occurring in switching power supplies (UPS). They have a fairly wide bandwidth, a developed synchronization system and make it possible to carry out a detailed analysis of a signal stored in memory, for example, a transient. However, due to the limitations of serial DSO architecture, the time between adjacent firings is long enough that important signal details can be lost. In addition, DSOs display all signal details with the same intensity, which also leads to inevitable loss of information.

As for the AOVR, they perfectly display the signals, allow you to reproduce them in detail even with a quick change. By definition, AODS provide gradations of image intensity on the screen, reflecting the frequency of occurrence of certain signal components. Unfortunately, these oscilloscopes do not store the signal, do not allow you to make any complex measurements and analyze the signal as a DSO. That is why designers are forced to use both of these devices when designing and debugging a UPS.

The task of combining the advantages of AOVR and DSO in one device - CLO - was solved with the advent of a new architecture for building oscilloscopes. It is based on "digital phosphor" technology, which digitally mimics the inherent change in image intensity of an AODS. In other words, DSO allows developers to see on the screen, for example, modulated signals and all their fine details, just like AODS, while providing their storage, measurement and analysis, like DSO.

Instantaneous power measurement with DLO

When developing a UPS, it is necessary to know the instantaneous values ​​of power dissipation in transistor power switches (TSK). It is the knowledge of this parameter that makes it possible to choose a TSC (for example, a powerful MOSFET in the circuit in Fig. 1), which would be inexpensive, but ensure reliable operation of the device. The instantaneous power measurement procedure includes differential measurements of the pulsed current in the respective circuit. The use of a differential probe is mandatory here, since we are interested in the drain-to-source voltage on the MOSFET (V ds in Fig. 1), and none of the terminals of this transistor is connected to the common wire. The DSO, like most other oscilloscopes, is not designed for direct measurements of such "floating" high voltages. The TekProbe level II DLO interface of the TDS3000 oscilloscope supports both the P5205 differential probe and the TCP202 current probe for exceptionally accurate instantaneous power measurements over a wide bandwidth.

Before carrying out such measurements, it is necessary to equalize the delays in the channels of the differential and current probes. This procedure is called "deskewing". The probes mentioned above are matched in signal delay to 2 ns accuracy, but other probes and other combinations of them may no longer provide such accuracy and must necessarily be subjected to the "deskewing" procedure. This is very important, because even small time differences between voltage and current measurements can lead to large errors in the measurement of instantaneous power values.

Like other modern digital oscilloscopes, DSOs have a memory that, in particular, stores the values ​​of the difference in delay times between different probes. It is measured with the help of the DLC according to the test signal, and then it is recorded in the memory of the DLC. The autoset function, which almost any DSO and DSO has, allows you to set the initial image parameters on the oscilloscope screen. The results of the "deskewing" procedure are automatically taken into account.

The color LCD screen is very convenient for displaying multiple signals at the same time. For example, you can assign different colors to voltage, current, and power waveforms. Thanks to the TekProbe level II intelligent interface, digital information will be accurately read and scaled in this case, so that additional interpretation of the results is not required.

DSO (like many DSOs) has the ability to mathematically process the studied signals. Therefore, for example, information about instantaneous power values ​​is obtained by simply multiplying - "point by point" - the current voltage value by the corresponding current value. On fig. 2 shows the results of measuring voltage and current and calculating the instantaneous power as they are displayed on the DLC screen.

Studying Modulated Signals

The ability of the DLC to display information with variable intensity greatly facilitates troubleshooting of the UPS, especially the determination of excessive signal modulation depth in the UPS output voltage regulation circuits. Too deep modulation is known to cause UPS instability. On fig. 3 shows the signal in the UPS output voltage control loop with less intensity in areas where the modulation is less frequent. DRO increases the intensity of the image in areas of the image where the signal appears most often, and this is similar to an analog oscilloscope.

The DSO is ideal for displaying such signals, as it has a very high signal acquisition rate - more than 50 times faster than DSO. In addition, the digital phosphor display makes it possible to observe the modulated signals in real time.

Transient Research

Registration of transient processes with DLC is very simple. This uses its edge triggering capabilities to set slope, level, link type, and trigger delay. If the UPS is already integrated into the system, it can be useful to synchronize the UPS 'problem' waveform under investigation with a signal taken from a test point in the system. This will allow, in particular, to identify the synchronism of transient processes in the system and the UPS and establish their relationship.

Of course, the DC output voltage of the UPS must be "clean" and without transients. Combining a display of information known as "scrolling" with peak signal detection allows the DLC to detect short duration transient pulses on slow varying signals or DC. When "scrolling", the image slowly "scrolls" from right to left, resembling the work of a recorder. The Peak Detector detects spikes in the signal with a minimum duration of up to 1 ns and changes the sweep rate to study them in detail.

Study of the harmonic composition

The study of the harmonic components of signals in power circuits is a very important task when designing a UPS. The fact is that they excite interference in the supply network - odd harmonics from pulse signals acting in the UPS. Moreover, when connecting to a network, for example, several computers, these interferences can be summed up and reach a noticeable level as a result. Since these components (interference) lead to increased heat generation in transmission lines and power transformers, they should be minimized (eg according to IEC 555 and IEC 10003-2). To solve this problem, a CLO with additional blocks is suitable.

For example, the TDS3000 can be fitted with an FFT module, making the oscilloscope an excellent tool for measuring harmonic distortion. In this case, it is possible to simultaneously display the signal under study and its spectral composition. The FFT can be used to process both live and stored signals.

Obviously, the purchase of such a unit is more cost-effective than the purchase of a specialized harmonic distortion analyzer. In addition, this allows developers to use not a new instrument, but an oscilloscope they already know well.

The procedure for measuring the harmonic components of a signal is no more complicated than conventional measurements of the parameters of periodic signals, since they are a repeating periodic sequence of pulses, and not a transient. To get good analysis resolution, you need to display at least five cycles of the signal under study on the oscilloscope screen (see Fig. 4).

The user can set a linear or logarithmic vertical scale and various options for FFT "windows" - rectangular, Hamming, Hanning and Blackman-Harris. For periodic signals, the Hamming window is most suitable. Linear scaling is commonly used in power measurements.

Documentation of measurement results is very important in device design. CLOs (as well as CSOs) provide ample opportunities for this, which greatly facilitates the preparation of reports. A special "hard copy" button allows you to print an image on an inkjet or laser printer (connected to the standard parallel port of the CLO). You can also save it to a floppy disk in various formats, including .BMP, .EPS, .TIF, etc.

DSO: a breakthrough in oscilloscope technology

The digital phosphor oscilloscope not only combines the best qualities of analog and digital instruments, but also significantly exceeds them. It has all the advantages of a DSO (from data storage to complex synchronization types), while at the same time providing the special capabilities of AODS (instantaneous response to signal changes and display of a signal with variable brightness). The latter was made possible by digital fluorescence emulation.

The new TDS3000 DSO series from Tektronix is ​​represented by six models of two- and four-channel oscilloscopes with a bandwidth of up to 500 MHz, which have a compact design, light weight (3,3 kg) and, as an option, autonomous power supply.

Author: A.Matvienko, Market Development Manager, Tektronix, (095)494-51-58

See other articles Section Measuring technology.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive The sun makes men hungry 24.07.2022 To maintain a figure, men should be less in the sun. This was found out by the staff of Tel Aviv University. Analyzing the statistics of a large medical project that collected various data on three thousand people aged 25 to 65, the researchers found that during the warm season, men consume 17% more calories than women. The most obvious explanation here is that the sun somehow stimulates appetite, and only in men. Experiments with volunteers confirmed this: if men and women are specially brought out into the sun, and then asked how much they want to eat, it turns out that men feel more hungry after the sun. But women will not feel the difference - the sun does not excite additional hunger in them. Appetite and the feeling of hunger depend on many physiological signals, including the hormone ghrelin, which is called the hunger hormone. (In general, there are several hunger hormones, but ghrelin is one of the most famous.) Ghrelin is synthesized in the stomach, from the stomach it enters the pituitary gland and hypothalamus, stimulating eating behavior, that is, it excites appetite, makes you focus on finding food, etc. Ghrelin levels rise before meals and, as it has now turned out, in the sun: in men who took a sunbath, the level of ghrelin in the blood increased (in women, its level in the sun remained the same). The same thing happened to mice that were irradiated with medium-wave ultraviolet, or ultraviolet B. Medium-wave ultraviolet is part of the solar radiation reaching the earth's surface, and mice were irradiated with it in such a way that the exposure was equal to a half-hour dose of the sun on a clear noon somewhere on latitude of Mexico, Cuba or Florida. The mice were irradiated every day for ten days, and those males who received regular portions of UV light tried to eat more often than females or males who were not irradiated. Ghrelin is synthesized not only in the gastrointestinal tract, it is also secreted by fat cells in the skin, and they secrete it under the action of the p53 protein. It is called the guardian of the genome because p53 monitors DNA damage: it either stimulates DNA repair or causes the cell to commit suicide so that it does not harm others with its mutations. Under the influence of ultraviolet activity of the p53 gene increases, because ultraviolet damages DNA. As a result, fat skin cells release more ghrelin. This is what happens in males; in females, the sex hormone estrogen suppresses the activity of the p53 gene, and the level of ghrelin in response to UV radiation does not increase in them. It can be assumed that the same mechanism with dermal ghrelin and p53 works in humans. But so far, it is impossible to say this with certainty. Other experts point out that little attention is paid to people in general in this study. Here we need to conduct an experiment with a large number of participants, and we also need to carefully monitor additional factors that can tie together the sun and appetite in men. However, in any case, we should be more careful with the sun: although we get vitamin D thanks to it, no one has canceled sunburn and ultraviolet mutations in skin cells.

Other interesting news:

▪ Sensors with liquid crystals that change color

▪ Synthesized lubrication for joints

▪ New miniature chips for battery maintenance

▪ Street lighting on request

▪ Dark Sky Conference

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Security and safety. Article selection

▪ article The battle of Russians with Kabardians. Popular expression

▪ article For what green revolution did Norman Borlaug win the Nobel Peace Prize? Detailed answer

▪ article Technologist. Job description

▪ article Low-frequency amplifier on the TDA1558 chip. Encyclopedia of radio electronics and electrical engineering

▪ article Sinhala proverbs and sayings. Large selection

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024