PSN-L Email List Message

Subject: Re: Testing the Folded Pendulum
From: "Geoffrey" gmvoeth@...........
Date: Sun, 29 Jul 2007 05:29:16 -0700

Have you seen the seismometer they are building for
a mars mission ? do you think you could duplicate
one like that ???
I think it is only horizontal x-y.


----- Original Message ----- 
Sent: Saturday, July 28, 2007 08:46
Subject: Testing the Folded Pendulum

Hi All,  I finished the Folded Pendulum Sensor.  I will send pictures to anyone interested.  After I test it, and if it works, I 
will then post the pictures on the internet, like I did on the "Slinky"

All in all, it was a bit of a bear.   I guess the fact it was a new concept, for me, and that I could find only a couple examples, 
was part of the issue.   Thanks to all who helped me, or I would have never gotten this far.   At this point it seems to be working, 
but I can qualify it's performance after it is tested.

The two pendulum, one normal, one inverted have the same length, 7.625",  The box it is contained in is 32"x24".
The best working natural period I could measure, was about 6 to 10 seconds.  I could obtain 15 seconds but it was too unstable.
It has been pointed out to me that I should have achieved a longer period using this approach.   Perhaps other articles and examples 
may show me how to improve the design.

By the way if and when I record earthquakes using the sensor I will post them on PSN as TCIDF, for "Folded Pendulum"
TCIDzs= "Slinky is setting in the corner.

I do have a question about measuring a sensor's period.  I assume the best way is to remove the damper, tap the arm, and time the 

Q.   Is there another way, to estimate its period, with the damper installed?   On this sensor the damper is difficult to remove.

Different Subject

Q.   I don't really understand the FFT in AmaSeis.   If I take one hour of trace, containing road construction noise, and use 
Control/Fourier Transform/Linear,   I see a large spike at 1.607Hz another at 2.597Hz and some other signals.
Is this the frequency of the noise?

Q.  I highlighted an earthquake, and using the same steps I see a section of spikes, starting at .2 and ending at .8Hz
Is that the frequency of the recorded earthquake?

Thanks Again,  Ted


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