PSN-L Email List Message

Subject: Re: Tests on folded pendulum instrument
From: "David H. Youden" dyouden@.........
Date: Mon, 17 Mar 2003 06:06:04 -0500


Jim,

I use Dataq"s Windaq software for a variety of reasons, so my recordings 
are not compatible with the more common formats. I do have a few, which I 
would be happy to share with anyone who can handle the file format, or I 
can make picture files of them in some common format e. g. GIF or JPG.

Dave...

At 09:59 AM 3/16/03 -0800, you wrote:
>Hi Dave-  You got my attention- Nice work!- Do you have any records
>(seismograms) posted that we can look at?
>Jim O'Donnell - UNLV
>On Sun, 16 Mar 2003 11:57:47 -0500 "David H. Youden" 
>writes:
> > All,
> >
> > I got a chance yesterday to run some tests on my instrument.
> >
> > Here's what I did:
> >
> > I opened the loop and drove the force balance coil directly with a
> > HP
> > function generator ( Model 3310B). I placed a 1000 ohm resistor in
> > series
> > with the coil. I took my input signal from across the coil so I had
> > a
> > sensitivity of 1000 volts/amp. The output was taken at the output of
> > the
> > cap gauge circuit, after a 2 pole 35 Hz filter that would have been
> >
> > inconvenient to remove. The output device was a HP 54603B memory
> > scope. The
> > driven mass is pretty close to 500 grams.
> >
> > I attempted to take phase and P-P position data at constant
> > acceleration
> > from 0.1 Hz to 10 Hz while holding the current through the coil at
> > 94
> > microamps, i. e. 94 millivolts across 1000 ohms. Why that value?
> > Because it
> > was the maximum that I could use at 0.1 Hz and still maintain
> > linearity of
> > the cap gauge signal.
> >
> > Results:
> >
> > The force balance coil/magnet combination have a transfer function
> > of 0.26
> > Newtons/Amp.
> >
> > I lost the signal in the noise at about 6 Hz. Obviously, I could go
> > higher
> > with a larger input signal.
> >
> > The phase between acceleration and displacement was less than 20
> > degrees
> > throughout the range.
> >
> > The P-P displacement was about 60 nanometers at 6 Hz.
> >
> > The laws of physics still apply, as the P-P position signal was
> > inversely
> > proportional to the square of the frequency.
> >
> > There was no sign of roll-off due to damping from the cap gauge, but
> > then
> > the amplitudes were pretty low at the higher frequencies.
> >
> > Comment: My low pass filters are set to roll off at 5 Hz so data
> > beyond
> > that point is academic.
> >
> > Dave ...
> >
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> >
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