Hi all,
 
  I have written a VB6 program which models a spring supported  vertical 
seismometer. If you want to build a vertical seismometer, you must  design it 
around the spring, since you cannot easily order a spring built to  your 
specifications. So, if you go to a hardware store and buy a spring, measure  its spring 
constant and calculate its relaxed length. You can then use my  program to 
see what kind of sensor could use the spring. I am willing to send  the program 
and illustrations to all who request them. Keep in mind that  building an 
amateur sensor does not easily result in achieving a useful natural  period of 
more than four or five seconds, but you can extend this using my  "WQFilter" 
program. The application was written to satisfy my own curiosity, and  is somewhat 
"user-surly". The program description follows:
-----
Subj: Design tool for vertical seismometer, "SpringCalc.exe", version  1.0.0.8
November 2004
 
  This program allows the user to model a spring-supported pendulum  
constrained to move in a vertical plane, and is a design aid for building a  vertical 
seismometer.
 
  There are a lot of data entry boxes to fill in, as you will see.  There are 
two boxes for characterizing the spring, two for point of attachment  of the 
spring to the pendulum arm, one for pendulum mass, one for pendulum  length, 
two for trial limits on spring angle, and one for the angle decrement  step 
size. The picture, "SchematicA.gif", shows the model for the sensor.  
"SchematicB.gif" show an alternate configuration, where the spring is suspended  downward 
from a boom attachment point on the other side of the boom hinge. In  this 
case, Xp is negative, and the spring angle is greater than 180 degrees. A  third 
configuration is shown in "SchematicC.gif", where a spring in compression  
pushes upward on the pendulum arm. One embodiment of this arrangement allows a  
leaf spring, approximately assuming a sideways "U" shape, to be used. This  
program assumes that such a spring is free to pivot at each end.
 
  Trial design numbers are already filled in. You can modify any of  the 
entries using mouse and keyboard, and store them for future use. The data is  
stored in file "SeisData.bin". What the program does is to stretch the spring in  
the spring angle direction to balance the pendulum. The X, Y coordinates are 
the  resulting upper attachment point of the spring.  It then displaces the  
pendulum from horizontal by one degree up and down to determine the restoring  
torque on the pendulum, and from that information, calculates a natural period  
of oscillation. You will note that the restoring torque can be negative,  
indicating a non-stable solution. If you should want to save the displayed  
results, you will have to select the text with the mouse, and use Ctrl-C to copy  
it to the clipboard, and from there to a Notepad document. The program starts  
with the highest spring angle entered, and iterates downward one step angle at 
a  time until either the lower limit, instability, or an iteration limit of 
50 is  reached, whichever occurs first. 
 
  Note that if you specify a spring angle of 90 degrees, and put the  mass at 
the same distance as Xp, you have the very nearly the equivalent of a  mass 
dangling from a spring. The resulting period is what you would expect from  the 
combination of spring constant and mass. At lesser spring angles, the period  
gets longer, until a limiting angle is reached, below which the pendulum is 
in  unstable equilibrium.  
 
  If you try a zero length spring for your model, you will find the  tuning 
up of the sensor will be very easy. It gets harder as the relaxed length  of 
the spring gets longer, and the value of "X" goes more negative (the upper  
spring attachment is farther behind the vertical drawn from the hinge).
----
Here are some links for amateur vertical seismometers
 
_http://jclahr.com/science/psn/wooden/_ 
(http://jclahr.com/science/psn/wooden/) 

_http://www.jclahr.com/science/psn/mcclure/vert2.html_ 
(http://www.jclahr.com/science/psn/mcclure/vert2.html) 

_http://quake.eas.gatech.edu/Instruments/LPVERT0.htm_ 
(http://quake.eas.gatech.edu/Instruments/LPVERT0.htm) 

The late Sean-Thomas Morrissey built a force feedback sensor. The  pendulum 
design is also suitable for open loop operation. See

_http://www.eas.slu.edu/People/STMorrissey/index.html_ 
(http://www.eas.slu.edu/People/STMorrissey/index.html) 
 
 
Bob McClure  
bobhelenmcclure at aol dot  com





Hi all,
 
  I have written a VB6 program which models a spring supported=20
vertical seismometer. If you want to build a vertical seismometer, you must=20
design it around the spring, since you cannot easily order a spring built to=
=20
your specifications. So, if you go to a hardware store and buy a spring, mea=
sure=20
its spring constant and calculate its relaxed length. You can then use my=20
program to see what kind of sensor could use the spring. I am willing to sen=
d=20
the program and illustrations to all who request them. Keep in mind that=20
building an amateur sensor does not easily result in achieving a useful natu=
ral=20
period of more than four or five seconds, but you can extend this using my=20
"WQFilter" program. The application was written to satisfy my own curiosity,=
 and=20
is somewhat "user-surly". The program description follows:
-----
Subj: Design tool for vertical seismometer, "SpringCalc.exe", version=20
1.0.0.8
November 2004
 
  This program allows the user to model a spring-supported pendulu=
m=20
constrained to move in a vertical plane, and is a design aid for building a=20
vertical seismometer.
 
  There are a lot of data entry boxes to fill in, as you will see.=
=20
There are two boxes for characterizing the spring, two for point of attachme=
nt=20
of the spring to the pendulum arm, one for pendulum mass, one for pendulum=20
length, two for trial limits on spring angle, and one for the angle decremen=
t=20
step size. The picture, "SchematicA.gif", shows the model for the sensor.=20
"SchematicB.gif" show an alternate configuration, where the spring is suspen=
ded=20
downward from a boom attachment point on the other side of the boom hinge. I=
n=20
this case, Xp is negative, and the spring angle is greater than 180 degrees.=
 A=20
third configuration is shown in "SchematicC.gif", where a spring in compress=
ion=20
pushes upward on the pendulum arm. One embodiment of this arrangement allows=
 a=20
leaf spring, approximately assuming a sideways "U" shape, to be used. This=20
program assumes that such a spring is free to pivot at each end.
 
  Trial design numbers are already filled in. You can modify any o=
f=20
the entries using mouse and keyboard, and store them for future use. The dat=
a is=20
stored in file "SeisData.bin". What the program does is to stretch the sprin=
g in=20
the spring angle direction to balance the pendulum. The X, Y coordinates are=
 the=20
resulting upper attachment point of the spring.  It then displaces the=20
pendulum from horizontal by one degree up and down to determine the restorin=
g=20
torque on the pendulum, and from that information, calculates a natural peri=
od=20
of oscillation. You will note that the restoring torque can be negative,=20
indicating a non-stable solution. If you should want to save the displayed=20
results, you will have to select the text with the mouse, and use Ctrl-C to=20=
copy=20
it to the clipboard, and from there to a Notepad document. The program start=
s=20
with the highest spring angle entered, and iterates downward one step angle=20=
at a=20
time until either the lower limit, instability, or an iteration limit of 50=20=
is=20
reached, whichever occurs first. 
 
  Note that if you specify a spring angle of 90 degrees, and put t=
he=20
mass at the same distance as Xp, you have the very nearly the equivalent of=20=
a=20
mass dangling from a spring. The resulting period is what you would expect f=
rom=20
the combination of spring constant and mass. At lesser spring angles, the pe=
riod=20
gets longer, until a limiting angle is reached, below which the pendulum is=20=
in=20
unstable equilibrium.  
 
  If you try a zero length spring for your model, you will find th=
e=20
tuning up of the sensor will be very easy. It gets harder as the relaxed len=
gth=20
of the spring gets longer, and the value of "X" goes more negative (the uppe=
r=20
spring attachment is farther behind the vertical drawn from the hinge).
----
Here are some links for amateur vertical seismometers
 
http://jclahr.com/science/psn=
/wooden/

http://www.jcl=
ahr.com/science/psn/mcclure/vert2.html

http://quake.ea=
s.gatech.edu/Instruments/LPVERT0.htm

The late Sean-Thomas Morrissey built a force feedback sensor. The=20
pendulum design is also suitable for open loop operation. See

http://www.eas=
..slu.edu/People/STMorrissey/index.html
 
 
Bob McClure  
bobhelenmcclure at aol dot=20
com