damping factor calculation

[alibo1984]

Hello, i'm tryng to calculate the damping factor and damping ratio from some data i gathered. I have plotted the results so i'm trying to use the logarithmic decreament method.

I have measured the amplitudes, so i have Xn and Xn+m, but i keep getting -ve results, and i'm sure thats not right. Surely i should be getting a value lower than 1 as the data clearly shows the system to be under damped.

Any thoughts on where i'm going wrong?

Cheers

 

[GregLocock]

You haven't given us much to go on.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[hacksaw]

sounds like you have found the log "increment" (the inverse)- but i agree not much of a description