Gary,

Thanks for passing along the link to your=20
site.  Looks like you've got it running pretty nicely.

This is probably a good time to provide the List=20
with a little history of the design and some=20
recognition of some of the other people who were=20
instrumental in its creation.  First must be=20
Angel Rodriguez, who operates the Seismic=20
Observatory of Western Panama, OSOP, and who=20
originally saw the need  for a high-quality, yet=20
simple instrument which was easy to repair in the=20
field and which could be manufactured in rural=20
Panama by local workers.  He wanted it to be as=20
simple as possible, (but not more so), and it was=20
to be reasonably large to make it easy to build=20
and fix.  If such an instrument could be=20
designed, it might be made available to the=20
seismological community in Cemtral and South=20
America as a simple but very useful instrument.=20
(He now manufactures it and has named it the Cais=E1n.)

To get things started, Angel contacted several of=20
us who had shown an interest in such designs and=20
encouraged us to see what could be=20
accomplished.  Dave Nelson first started thinking=20
about the design and early on visited Terry Brown=20
in Tennessee to discuss how such an instrument=20
might look.  The Inyo Force-Balance Vertical and=20
Cais=E1n owe much of their mechanical design to=20
Terry's original concepts.  Dave then took=20
Terry's ideas, refined them, and started=20
construction and circuit design.  At around that=20
time I got involved, mostly helping with some of=20
the software tools required to analyze and create=20
the design, consulting on the circuit and=20
discussing troubleshooting approaches with Dave=20
when it wasn't working right (which at first was=20
discouragingly often).  A number of other people,=20
including, in particular, Chris Chapman added=20
their ideas and suggestions to the effort.

I just wanted to share the whole story.  The Inyo=20
has turned out to work much better than we had=20
thought would be possible and it is clear so far=20
that local site noise will be the limiting factor=20
on what it can see.  Under good conditions you=20
can sometimes see surface waves from magnitudes=20
in the high 4's, if they are oriented right.

Many thanks to all who helped with the design,=20
and in particular to Gary, Karl and Barry, who=20
have been of enormous help in aiding our=20
understanding of what sort of support and=20
documentation will be most useful for those who follow.

Regards,
Brett


At 02:35 PM 3/13/2010, Gary Lindgren wrote:
>Matt,
>I suggest you check out the Inyo FBV (Force Balance Vertical) seismometer
>designed by Dave Nelson and Brett Nordgren. The seismometer is very
>sensitive and picks up M5's half way around the world. Karl Cunningham,
>Barry Lotz, and I have built one of these units. Check out
>http://sites.google.com/site/seismicsensorinfo/ This site chronicles the
>design process I went through to build this amazing instrument. Brett's
>loop7 spreadsheet guides you through the design details. You enter the
>bandwidth you want, go through a few steps and out pops capacitor and
>resistor values you need to fill the circuit board. Let me know if you any
>questions.
>Gary
>
>
>
>
>
>
>Gary Lindgren
>585 Lincoln Ave
>Palo Alto CA 94301
>
>650-326-0655
>
>www.blue-eagle-technologies.com  Check out Lastest Seismometer Reading
>cymonsplace.blogspot.com
>sites.google.com/site/seismicsensorinfo/Home    Design Details for New
>Vertical Seismometer
>
>
>
>
>
>-----Original Message-----
>From: psn-l-request@.............. [mailto:psn-l-request@............... On
>Behalf Of Matt Zieleman
>Sent: Saturday, March 13, 2010 10:36 AM
>To: psn-l@..............
>Subject: Vertical BB derived from STM-8
>
>I've been doing some conceptual design work on a vertical broadband
>sensor, and I have a few questions. By reading past archives of the
>PSN-L I noticed that Sean-Thomas Morrissey was a contributor to this
>list, and there was some discussion about his STM-8 vertical
>leaf-spring design.
>
>1.) My first question is about deriving the transfer function. I tried
>to derive it myself, but from first principles, but what I got isn't
>what is shown in Sean-Thomas' work. I think the problem is my
>understanding of what the input and output of the transfer function
>are. Here's my logic for the transfer function:
>
>You can't measure the position of the Earth's surface from a
>stationary reference frame, and you can't measure the position of the
>mass from a stationary reference frame. Only the relative position
>between the two can be measured. My first postulate is that the force
>acting on the mass only depends on the relative position of the mass
>and Earth's surface. Combining this postulate with Newton's F=3D ma, I
>get:
>
>           s^2 * M * X(s) =3D F(s) * (Y(s) - X(s))
>
>Where M is the mass, X(s) is the position of the mass in a stationary
>frame, Y(s) is the position of the ground in a stationary frame. The
>only thing we can directly measure is Y(s) - X(s), so I believe the
>transfer function is from Y(s) to Y(s) - X(s)/
>
>           Now X(s) =3D Y(s) - (Y(s) - X(s)), substituting in the left
>hand side of my above expression:
>
>           s^2 * M * (Y(s) - (Y(s) - X(s))) =3D F(s) * (Y(s) - X(s))
>
>           s^s * M * Y(s) =3D (F(s) + s^2 * M)(Y(s) - X(s))
>
>                                       s^2 * M
>           (Y(s) - X(s)) =3D ----------------------- Y(s)
>                                 F(s) + s^2 * M
>
>Then F(s) would be k + s*eta + K_p  + s * K_d + K_i /s where K_p, K_i,
>K_d are the coefficients of a PID controller, k is the mechanical
>spring constant, and eta is the mechanical damping, if any.
>
>When I plug this all in I get a somewhat simpler expression.that what
>Sean-Thomas had. So I went back on including that fact that the
>integrator pole is not zero, and the back EMF generated in the
>feedback coil, and wound up with something way more complicated that I
>am not going to type out here. Does anybody have any hints?
>
>2.) My second question is about the hinge. Is foil suitable or should
>I look at something like a knife edge or ball bearing hinge? I'm
>leaning strongly towards foil. How much of an impact does the
>flexibility of the foil really have on the period? Given that the
>spring constant of the main spring is probably much much larger.
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>
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>
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>
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>
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