Subject: Re: Lehman seismograph


> Hi PSN members. Thanks for welcoming me to the PSN network. I have
recently decided to build the Lehman seismograph.. I have completed the
Transducer part of my "Lehman" and I am about to build an amplifier (which I
dread[can they be purchased or "requisitioned" anywhere])?. I have a small
problem though and I hope that you may have some thoughts on it. The only>
feasable place for me to place the seismograph seems to be in my basement
> which has a thin carpet in it over a concrete floor. Do I need to cut the
> carpet away(the size of the Lehman base)? What do you think of the idea of
> using VERY LARGE and SHARP screws that would penetrate the carpet and they
> can also be used for Leveling? I have heard of some people using their
> seismographs on other than the ground floor (wouldn't the waves be
baffled/diminished)?
> Any thoughts would certainly be appreciated. Thank you very much, Ed.
>
>
>
>
>
>
>
>
> ----- Original Message -----
> From: "Larry Cochrane" 
> To: "Ed Ianni" 
> Sent: Monday, December 18, 2000 12:41 AM
> Subject: Re: Lehman seismograph
>
>
> > Ed,
> >
> > First go back to the knife edge. Since a Lehman is a horizontal sensor
you
> > only want horizontal movement of the boom. To get the boom to stabilize
> you
> > need to position the top pivot point (where the wire meets the holder)
> > slightly before the bottom pivot point (the knife edge). As the angle
> > becomes straight up and down the boom will become more unstable. This is
> > also how you set the period. The period will increase as the angle
becomes
> > more straight up and down. You can adjust the angle by lifting up the
back
> > end of the sensor. This will change the top and bottom angle. First
start
> > with a large angle and no damping. The boom should come too rest in the
> > center of the sensor. As you lower the backend of the sensor the
> oscillation
> > period should increase. At some point the boom will become unstable. At
> that
> > point increase the angle a little and check the period. It should be
> between
> > 10 and 20 seconds.
> >
> > Hope this helps and good luck.
> >
> > -Larry Cochrane
> > Redwood City, PSN
> >
> > ----- Original Message -----
> > From: Ed Ianni
> > To: cochrane@..............
> > Sent: Saturday, December 16, 2000 7:28 PM
> > Subject: Lehman seismograph
> >
> >
> > Dear Mr. Cochrane;
> >         I am building the Lehman home seismograph. I am unable to get
the
> > boom stabilized although everything is level. I have used a "knife
point"
> > and a "rounded end" but the centering of the boom remains difficult and
> > inconsistent. Any suggestions would help. Thank You Very Much. Ed.
> >
> >
>

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)