Thanks for the article, this answered my questions.
Ted

--------------------------------------------------
From: "Charles R Patton" 
Sent: Tuesday, June 11, 2013 10:42 AM
To: 
Subject: Re: Water/Laser geophone instrumentation

> Ted,
> Check out the PSN email
> VBB-BB Tiltmeter info
> 5/5/2001 11:45 PM
> from S-T Morrissey
> This was the project he was working on just before he died.
> 
> In addition a Chris  email references the NSF (National Science 
> Foundation) paper:
> Check out the PSN email
> Re: Morrissey Balance-beam Tiltmeter
> From:ChrisAtUpw@.......
> Date:Thu, 25 Dec 2008 22:40:21 EST
> This contains info that the project was finished.  I have a copy of the 
> NSF proposal (not the final report).  It includes data on proposed 
> sensitivity, notes on balance beam construction and proposed transducer 
> methods and problems.   I will email the 1.05MB file to interested 
> folks. I don't have the final report mentioned by Chris.
> 
> The abstract mentioned above is:
> ********start quote*******
> Abstract submitted for 2000 fall AGU meeting:
> 
> Updated 10 December, 2000
> 
> A Beam-Balance Broadband Tiltmeter That is Insensitive to Horizontal 
> Acceleration.
> 
> Sean-Thomas Morrissey (Dept. of Earth and Atmospheric Sciences, St.Louis 
> University, 3507 Laclede; St. Louis MO, 63103; 314 977 3129; 
> sean@.............
> 
> A new broadband seismic instrument has been developed that is sensitive 
> only to "pure" tilt and not to horizontal acceleration.
> 
> A new beam-balance tiltmeter has been developed that does not respond to 
> horizontal ground movement. Since all horizontal seismometers are also 
> tiltmeters they are sensitive to tilt, especially at longer periods, and 
> seismic data can be compromised in the period range of 20 to 3000 
> seconds. The most important noise source in the horizontal data is 
> tilting of the pier, mostly due to barometric loading. But all 
> tiltmeters, up to now, are also seismometers, (ie. they are sensitive to 
> horizontal translation), so can not be used to separate tilt noise from 
> seismic signals.
> 
> Our new beam balance tiltmeter does not respond to horizontal 
> acceleration because the masses at each end of the horizontal beam are 
> suspended through the exact center of mass. This system is inherently 
> unstable, so broadband feedback is used to control it. With appropriate 
> feedback, the beam remains relatively horizontal when the base is 
> tilted, and the output is the relative motion at the displacement 
> detector. There is no rotation or output when the base is translated 
> horizontally along the axis of the beam.
> 
> The beam-balance tiltmeter is designed with separated lead masses 
> mounted in an aluminum bar that is suspended exactly at the center of 
> mass of the horizontal beam with a new low torque hinge flexure. The 
> center of mass is trimmed by a unique vertical mass centering adjustment 
> above the flexures. Displacement transducers and compact force feedback 
> coils with rare-earth magnets are placed at both ends of the beam.
> 
> Three sensors have been assembled as "proof of concept" prototypes. One 
> instrument is operating at station CCMO, near Saint Louis University, 
> and data from it are being digitized. Another is on a table and can be 
> used to demonstrate that tilt can be separated from horizontal 
> acceleration by simply sliding it horizontally. The static or DC tilt 
> sensitivity of the prototype is about 120 millivolts per microradian, 
> and the resolution is better than 0.1 nanoradian. Initial comparisons 
> using data generated by large quakes on the horizontal components of 
> nearby broadband seismic stations (18 km distant) show that the response 
> to horizontal acceleration is reduced by a factor greater than 1000 
> while maintaining the equalivant tilt sensitivity of the seismometer.
> 
> Ideally, the noise recorded in the tiltmeter output will exactly emulate 
> the tilt noise from the seismometer, at least in the flat portions of 
> their broadband velocity response. The success of this new instrument 
> has a tremendous implications for broadband stations in all regions of 
> the world where tilting from barometric, thermal, hydrologic, etc., 
> effects may limit the usefulness of the horizontal data.
> *********end********
> Regards,
> Charles R. Patton
> 
> 
> On 6/11/2013 8:19 AM, Ted Channel wrote:
>>
>> Hi All,  Chris your rain gutter idea is very interesting too.  Is 
>> there a pict illustrating the version of the Cascades used?
>>
>> Here is a different question...   Picture a perfectly balanced beam, 
>> on a center pivot, just like a see-saw, with two kids of similar mass.
>> Would this beam tend to remain fixed during an earthquake?    I can 
>> visualize, how a diving board with a person on the end would respond, 
>> with the mass moving differently from the earth.   But I don't know if 
>> the see-saw, would tend to remain fixed/level as the earth isolated 
>> during an event.
>>
>> cheers, Ted
> 
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