Oscilloscopes seem to be omnipotent, but they are not.

In electronic circuit design, we often encounter situations where we need to use an oscilloscope for measurement. Oscilloscopes play a relatively important role in circuits. In many cases, oscilloscopes are needed to measure some parameters in the circuit and make corresponding adjustments. Oscilloscopes can even measure electromagnetic interference. Various experts also use oscilloscopes to complete various functions. So it seems that oscilloscopes can do everything. So are oscilloscopes really that magical?

　　
In the history of electronic measuring instruments, the oscilloscope is the instrument with the greatest influence, the widest application, and the most varieties of products. It can measure and display almost all physical quantities and dynamic processes when equipped with appropriate non-electrical transducers. In short, any periodic physical process that can be converted into an electrical effect can be observed with an oscilloscope.

　　
The significant advantages of an oscilloscope
　　
are that it is very intuitive, can display waveforms directly on the screen, and can also be recorded permanently by photography. It has a large range and can measure signals ranging from a few microvolts for a high-sensitivity oscilloscope to tens of thousands of volts for a high-voltage oscilloscope. It has high input impedance and has minimal impact on the system being measured. It has rapid response, minimal electron beam inertia, and can display fast processes at the nanosecond level. It has multiple channels and can display several processes simultaneously on the same screen, making it easy to observe, compare, measure, and analyze. It has strong overload resistance and can work in harsh environments.
　　

Current understanding of the omnipotence of oscilloscopes
　　
On the one hand, oscilloscope manufacturers are constantly improving the test performance of oscilloscopes in response to various problems that occur when oscilloscopes test nonlinear load voltage characteristics. On the other hand, electrical engineers face many problems when using oscilloscopes to display the waveforms of switching power supplies, such as extremely low waveform resolution, serious noise signals and harmonics, and poor waveform reproducibility, but they do not know where the crux of the problem lies.

　　
In what circuit structure tests will the oscilloscope be "powerless"?

　　
When the oscilloscope is inserted into the red box area of ​​the following switching power supply circuit for sampling.
　　

Below are some truths about oscilloscopes. Come and see if you know them.

　　
What you see is always a fragment, not the whole thing, whether it is an analog or digital oscilloscope.
　　

The old man is judging right and wrong with a magnifying glass. In addition to the bandwidth limitation of the oscilloscope itself, the external probe also has a mirror. Sometimes, this mirror is very blurry and filters out many high-frequency details. But he still thinks the display is very clear, but there is no high-frequency trace in the photo. He says that the thing has never "come".
　　

I always like to stand in line. As the saying goes, it is better to stand in the wrong line than to be born in the wrong family. For example, pigs are originally slaughtered for meat. But what if pigs stand in the breeding line? Not only do they not have to worry about being slaughtered, but they can also eat delicious food every day. The same is true for oscilloscopes. I always like to use a ground wire to connect the probe and the earth to show that I am firm and upright. Engineers who don't know the truth often mess it up (the ground wire is clamped to the non-ground wire), or even break it into pieces.