Finding the Decay Time Constant: Tips and Tricks for Using an Oscilloscope

[MissP.25_5]

What is the decay time constant of the waveform? How to determine it from this oscilloscope?
The waveforms are in the pictures below:

 

[rude man]

Look at the 100 ns/div. oscillograph (the orhers are useless).

How long would you estimate it takes the bottom trace to get to 63% of its way to the top?

(This would be just an estimate since there may be nonlinearities involved, or two or more time constants. But a pretty good estimate anyway).

 

[MissP.25_5]

Look at the 100 ns/div. oscillograph (the orhers are useless).

How long would you estimate it takes the bottom trace to get to 63% of its way to the top?

(This would be just an estimate since there may be nonlinearities involved, or two or more time constants. But a pretty good estimate anyway).

Thanks for replying but could you explain this method, please?

 

[rude man]

Thanks for replying but could you explain this method, please?

Your trace begins at the bottom and ends at the top. How much time along the time axis to reach 63% of the distance from the bottom to the top? Use the 100 ns/div. trace.

 

[MissP.25_5]

Your trace begins at the bottom and ends at the top. How much time along the time axis to reach 63% of the distance from the bottom to the top? Use the 100 ns/div. trace.

Should 8~10ns be correct?

 

[rude man]

Should 8~10ns be correct?

Yes.
To get a better estimate you should have run 10 ns/division instead of just 100 ns.

 

[MissP.25_5]

Yes.
To get a better estimate you should have run 10 ns/division instead of just 100 ns.

Actually, 100ns is the sweep time.

 

[rude man]

Actually, 100ns is the sweep time.

Actually, I know.

You should have chosen 10 ns/div. sweep time

 

[MissP.25_5]

Actually, I know.

You should have chosen 10 ns/div. sweep time

Well, I just followed the procedure in the textbook. It says to set the sweep time to 2.5mircrosec, 250nsec and finally 100nsec.
I tried calculated the decay time and taking the best point that I could and I got 9.2ns. Is this ok? By the way, thanks for helping me out.

 

[rude man]

Maybe your oscilloscope didn't have a 10 ns.etting.

Anyway, I think your number is fine.