Summary of frequently asked questions by Macosin oscilloscope users (Part 1)

Does an oscilloscope with a bandwidth of 200MHz mean that it can measure signals with a maximum frequency of 200M?

A: Bandwidth is the basic indicator of an oscilloscope. When using an oscilloscope with a bandwidth of 200MHz to measure a 1V, 200MHz sine wave, the amplitude will be attenuated to only 0.707V. However, if it is a square wave or a triangle wave signal, it cannot be deduced in this way. It is necessary to perform spectrum analysis in the way of Fourier transform, depending on how many times of internal harmonics you pay attention to. For example, for a 40M square wave signal, according to the principle of spectrum analysis, only the 5th harmonic of 200M can be seen at most, and harmonics above the 5th cannot be seen. You may see that the square wave has become a curve with a certain arc. Of course, after the signal exceeds the bandwidth, only the amplitude is attenuated, and the frequency is not attenuated. If you only pay attention to the frequency parameters, there is no such concern as above. The measurement frequency of a 200M square wave is still 200M. When we choose an oscilloscope, in order to achieve a certain measurement accuracy, we generally choose a bandwidth that is 5 times the highest frequency of the signal.

What do the positive and negative overshoot, C root mean square, C average value, and burst pulse width in the oscilloscope measurement items mean?

Answer: Positive overshoot = [(maximum value - high value) / amplitude] * 100%; negative overshoot = [(low value - minimum value) / amplitude] * 100%; C in C root mean square and C average value is the abbreviation of cycle, C root mean square represents the effective value of the first cycle on the oscilloscope screen, and similarly C average value represents the average value of the first cycle on the oscilloscope screen; burst pulse width refers to the time from the first rising edge to the last falling edge on the oscilloscope screen.

What are the differences between the three data formats of WAV, CSV and BIN in oscilloscope?

Answer: When saving a WAV data file, the waveform data displayed on the screen will be sampled and saved as a binary file, which can be called on the oscilloscope to open, view, zoom, etc.; CSV is a comma-separated value file format, and its file stores table data in plain text. It will convert the required binary data into ASCII code and save it as ASCII code data. It can be opened with Excel, Matlab or text files, etc., and cannot be called by the oscilloscope. The data file saved in CSV is also sampled. Assuming that the 28M stored data is complete, there will be 28 million rows. If the oscilloscope is asked to calculate and save, it may take several hours. The BIN file format solves this problem. The BIN format can save the data completely in a short time, and then we only need to use a small software on the computer to convert BIN into CSV, which is equivalent to handing a large amount of calculation pressure to the computer.

What is the function of scrolling on an oscilloscope?

A: When the oscilloscope is in a large time base, it means that the waveform time to be observed is also extended accordingly. For example, if the time base is set to 1 second, there are 14 grids on the horizontal axis of the oscilloscope, which means that the waveform on one screen is 14 seconds. If we want to see a 14-second waveform, we have to wait 14 seconds in theory. In the scrolling mode, the waveform scrolls from right to left to refresh the display, and the waveform shape can be seen immediately. This mode is generally used to observe waveforms with frequencies below 5Hz.

What is the afterglow function of an oscilloscope used for?

A: Persistence refers to the trace left by the waveform on the screen. The duration of persistence can be set between 100ms and 10s, or it can be set to infinite persistence, which means that the position where the waveform appeared on the screen will not disappear. Using infinite persistence can measure noise and jitter, view the worst case of changing waveforms, find timing violations, or capture rare events.

How much voltage can an oscilloscope measure?

A: The maximum input voltage of the oscilloscope channel itself is around CAT I 300Vrms, but this does not mean that the oscilloscope can only measure a maximum effective value of 300V, because the signal enters the oscilloscope after being attenuated by the probe, so the voltage that the oscilloscope can measure often depends on the probe we use. The passive probe that comes standard with the oscilloscope can measure a peak value of 600V, and there are also high-voltage probes on the market that can measure thousands or even tens of thousands of volts.

What is the use of the HDMI function of an oscilloscope?

Answer: The HDMI function is to connect the oscilloscope screen to a projector. It is often used in the education industry to give demonstrations and explanations to students, or for live streaming, etc.

What should I do if there is interference in oscilloscope measurement?

A: The function of an oscilloscope is to restore the real signal. The higher the performance of the oscilloscope, the more details of the signal can be observed, and these details are often the key to discovering abnormal problems. In actual use, the interference in the surrounding environment is real. The sensitivity of a low-performance oscilloscope is very low. While choosing to ignore this part of the interference, it also misses a lot of useful information of the signal itself, making it impossible to perform effective and correct analysis; high-performance oscilloscopes also provide more diverse signal processing methods. You can use the bandwidth limit function in the vertical menu to help you perfectly filter out this part of the signal. You can also choose average sampling, noise suppression, etc. to help us achieve the desired observation effect.

Why does the waveform lag when it is moved when the time base tone is large?

A: The problem of visual waveform lag when the oscilloscope is at a large time base is caused by the working principle of the oscilloscope. The signal on one screen of the oscilloscope is a waveform of a period of time. The specific time is the current time base level * the number of grids in the horizontal direction. When our finger moves the waveform to a new position, the oscilloscope will re-intercept the signal. When the time base level is larger, the interception time will be longer, so it will give you the illusion that the response speed is "lag". If you don't care about the signal before the trigger, or don't need to use the trigger function of the oscilloscope to capture the desired waveform, then switching the oscilloscope to the ROLL mode will also work, and the waveform will be gradually updated.