Re: [Phys-l] Q from amplitude width?

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2011, Apr 25, , at 16:19, brian whatcott wrote:

> It is more conservative to establish what the resonances are in the 
> drive coil, rather than model
> it as an L and R in series, but better to check the drive current too.
>
> Not sure what frequencies are given as ~5.5 R, so let me ask directly: 
> what is the resonant frequency of the mechanical pendulum that you are 
> using?
>
> Brian W
> _________


At 100Hz my LCR SRS meter displays ~ 200mH and Q ~ 0.3  at 10kHz the Q rises to ~ 30, so I suppose, as  any coil will have a resonance from the distributed capacitance.  (assuming the wire is copper and not nichrome!)

~ 5.5 / 2Pi ~  0.88Hz.


If you go to:

http://www.cleyet.org/Pendula,%20Horological%20and%20Otherwise/Pendulum%20response%20to%20E-M%20harmonic%20drive%20as%20a%20function%20of%20bob%20mass/Pendulum%20response%20to%20E-M%20harmonic%20drive.tiff

You will see the summary of what I've put so far. 

I immediately plan to plot the drive and response on the same graph, à la J. Denker's suggestion.  I suspect I can even do some manipulating and find the tangent and verify according to:

tan( )  = 1/Q) ( 1 / (C1 - 1/ C1)    where C1 = natural (resonance freq.) / drive frequency


bc