Hi Ted,

My understanding of a long period physical pendulum is that 
sensitivity to ground motion is sacrificed in order to obtain the 
long period.  Your Ch3 is probably working correctly, but is MUCH 
less sensitive to ground motion than your Ch1 or Ch2.  That would be 
consistent with your observations.

Cheers,
John

At 05:24 PM 3/22/2008, you wrote:
>Hi Folks,  I just posted three data files, of the 6.2M ANDREANOF 
>ISLANDS, ALEUTIAN IS. 080322.212412 as ch1, ch2 and ch3
>
>Channel 1 is what I call a tiltmeter, just a normal pendulum with a 
>2 second period.  It can only swing East and West.  It works well
>Channel 2 is a vertical Spring Slinky II, also has a 2 second period.
>Channel 3 is my newest on called a Nearly Balanced, a normal 
>pendulum, with a 20 second period, It can only swing North and South.
>
>Channel 1 and 2 recorded the event well.
>Channel 3 did not record it at all.   I know it is working, as all 
>three are recording the road construction, all three show the same 
>large backhoe at the same moment in time.
>Channel 3 is also sensitive to me moving around the upstairs.
>
>I posted all three and filtered Channel 1 and 2, using Low pass 1, 
>and High pass .05..   These filters did nothing on channel 3 so I 
>posted it unfiltered.
>Perhaps someone can look at all three, to see if I have a 
>problem.   I don't think it is over damped, if anything it is 
>under.   Could this be the direction the channel is facing?
>
>Thanks, Ted


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