PSN-L Email List Message
Subject: Re: Tests on folded pendulum instrument
From: Jim ODonnell jimo17@........
Date: Sun, 16 Mar 2003 09:59:37 -0800
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"
> 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
> function generator ( Model 3310B). I placed a 1000 ohm resistor in
> with the coil. I took my input signal from across the coil so I had
> sensitivity of 1000 volts/amp. The output was taken at the output of
> 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
> from 0.1 Hz to 10 Hz while holding the current through the coil at
> 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.
> The force balance coil/magnet combination have a transfer function
> of 0.26
> I lost the signal in the noise at about 6 Hz. Obviously, I could go
> with a larger input signal.
> The phase between acceleration and displacement was less than 20
> 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
> proportional to the square of the frequency.
> There was no sign of roll-off due to damping from the cap gauge, but
> the amplitudes were pretty low at the higher frequencies.
> Comment: My low pass filters are set to roll off at 5 Hz so data
> that point is academic.
> Dave ...
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