Hi, i want to measure the time constant of an underdamped system.

Do i find 0.63*(max value) or 0.63*(settling value)?


(im trying to find the time constant of this graph)

thanks

 

Maybe this picture may be useful to judge https://dademuchconnection.files.wordpress.com/2017/11/null144.png?w=364&h=234
And here bit more extensive explanation https://lpsa.swarthmore.edu/Transient/TransInputs/TransStep.html
If more simple terms, see http://hyperphysics.phy-astr.gsu.edu/hbase/oscda.html just measuring the amplitude You can obtain only the damping factor, but looking for time may get only the tank period
Yet true the damping factor gamma makes a minor impact to the period, its truly tiny, less than a percent, as an example 0,632--> 0,628. w(fact)=sqrt(w(zero)^2 minus gamma^2)

 

Maybe this picture may be useful to judge https://dademuchconnection.files.wordpress.com/2017/11/null144.png?w=364&h=234

Oh ok thanks. So it's 0.63*(settling value)?

what is confusing me is that i was analysing a first order system and i got a similar result to the picture I initially uploaded which looks like a second order system. How is this possible?