In a message dated 27/10/05, rgroleau@....... writes:

>   http://users.rcn.com/rgroleau/seismo/index.html

Hi Rick,

       This is a very commendable effort! Well done.

       I am not able to associate the various Al beams and dimensions in your 
list with the components list for the seismometer - the list seems to be 
incomplete. 

       I did notice two things. The period is relatively short at 10 secs and 
only just extends beyond the large ocean background signals at ~ 6 secs. I 
also noticed that you had specified an angle of 8 sec from the vertical. It is 
desirable to run this type of seismometer at about 20 sec to also measure the 
longer period Love waves.
       I think that the 8 sec angle should probably be 8 min - I would 
estimate a period of about 20 sec from this.
       The problem with this design is that you have a very low moment of 
inertia. I estimate that the weight of the two long Al arms is about 1 lb each. 
You would get a much improved period and easier setup, if you added this amount 
of weight to the end of the arm, close to the coil. A suitable mass might be 
two 6" long by 1" square brass bars mounted vertically on the end of the beam
        You will probably have to use separate magnetic damping. You existing 
system is underdamped by your description. I can send you a drawing of the 
system that I use, with a copper plate and four NdFeB magnets, if it would be of 
intrerest. You might mount a horizontal copper damping 'tongue' at the level 
of the centre of the brass mass rods, on the opposite side of the vertical 
column to the pickup coil.
       I can also send you the circuit diagram of the fairly simple low noise 
amplifier that I use. 

       Regards,
       
       Chris Chapman
In a message=20=
dated 27/10/05, rgroleau@....... writes:



  http://users.rcn.com=
/rgroleau/seismo/index.html




Hi Rick,



       This is a very commendable effort!=20=
Well done.



       I am not able to associate the vari=
ous Al beams and dimensions in your list with the components list for the se=
ismometer - the list seems to be incomplete.=20



       I did notice two things. The period=
 is relatively short at 10 secs and only just extends beyond the large ocean=
 background signals at ~ 6 secs. I also noticed that you had specified an an=
gle of 8 sec from the vertical. It is desirable to run this type of seismome=
ter at about 20 sec to also measure the longer period Love waves.

       I think that the 8 sec angle should=
 probably be 8 min - I would estimate a period of about 20 sec from this.

       The problem with this design is tha=
t you have a very low moment of inertia. I estimate that the weight of the t=
wo long Al arms is about 1 lb each. You would get a much improved period and=
 easier setup, if you added this amount of weight to the end of the arm, clo=
se to the coil. A suitable mass might be two 6" long by 1" square brass bars=
 mounted vertically on the end of the beam

        You will probably have to use=
 separate magnetic damping. You existing system is underdamped by your descr=
iption. I can send you a drawing of the system that I use, with a copper pla=
te and four NdFeB magnets, if it would be of intrerest. You might mount a ho=
rizontal copper damping 'tongue' at the level of the centre of the brass mas=
s rods, on the opposite side of the vertical column to the pickup coil.

       I can also send you the circuit dia=
gram of the fairly simple low noise amplifier that I use.=20



       Regards,

       

       Chris Chapman