maychang

zhaoyanhao posted on 2018-7-19 22:23 Hello, I said last time that "I didn't post the evidence because of time constraints, please forgive me" and you thought that I didn't answer your request to post the evidence...

In the second picture, the leading edge of the first negative pulse on the oscilloscope is obviously tilted, not vertical, while the leading edge of the second positive pulse is vertical. This is often a manifestation of insufficient simulation step size. In addition, you only did two simulations. You might as well change the values of these two components and simulate them several times. This will make it easier to find the pattern.

maychang

zhaoyanhao published on 2018-7-20 09:29 If the simulation is not ideal, then the actual measurement will not be ideal either

If the simulation settings are not appropriate (such as the step size setting), it may be worse than the actual measurement. What is the basis of the simulation? It is the calculated result. The simulation calculation is completely based on the theories and formulas in the "Circuit Analysis" textbook, there is no doubt about this. If the theories and formulas in "Circuit Analysis" are wrong, the simulation results must be wrong (not in line with the actual situation). Conversely, the wrong simulation results cannot mean that the theories and formulas in "Circuit Analysis" are wrong. This logical relationship must be established.

maychang

zhaoyanhao posted on 2018-7-20 09:28 The test results are the same as the simulation results, but they are not saved. I don't have to make up stories to tease you

Of course you don't have to make up stories. However, the weather is so hot, and I don't have to type out my replies one by one on the keyboard, and even draw pictures to illustrate some replies. Is that right? Why did senior netizens like chunyang reply in this way? I think one of the reasons is that they want to summarize their thinking methods.

maychang

zhaoyanhao published on 2018-7-20 09:29 If the simulation is not an ideal situation, then the actual measurement will not be an ideal situation either

The theoretical formulas in textbooks such as "Circuit Analysis" can certainly be questioned. However, we must also pay attention to the direction, otherwise, after thinking for a long time, we will go astray and waste time and energy. If the simulation or actual measurement does not match the ideal situation, it is often because the simulation settings are not appropriate (as mentioned above, the basis of simulation is circuit theory), the distributed parameters that cannot be shown in the circuit are not taken into account in the actual measurement, etc. For example, taking the simulation diagram above as an example (the actual measurement is the same), your capacitance is 1pF. It should be noted that the capacitance between the two test leads of a multimeter is much larger than 1pF. It can reach 10pF when not twisted (of course this is not an accurate value), and it is even larger when twisted. The capacitance between the two leads of the 1 megohm resistor in the figure may also reach 1pF. If these distributed parameters are not taken into account, the results will certainly not be ideal.

zhaoyanhao

maychang posted on 2018-7-20 09:39 Of course you don't have to make up stories. But the weather is so hot, and I don't have to type out replies word by word on the keyboard, and even some replies have to be...

Thank you very much, those are all sincere words, of course I still have many shortcomings, thank you for your advice. I really haven't considered the details of the step length, I will think about it again, and I'm sorry to bother you.