PSN-L Email List Message

Subject: RE: two home-made vertical seismometers
From: "Kareem at HeyJooJoo" system98765@.............
Date: Thu, 23 Feb 2006 18:31:07 -0800

Hey Barry, 
Thanks for the info. I'll have a look. I actually have a PS2 recording
system by Kinemetrics. It's a portable system which came with a vertical
geophone (L4). It's great for local events as imagined but not so good for
distant more common events. So  I figured that it may be time to attempt to
build one. Message is certainly not too wordy but rather appreciated. I'm
still quite knew on the concepts of short period versus long period. 


-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of Barry Lotz
Sent: Wednesday, February 22, 2006 7:56 PM
To: psn-l@..............
Subject: RE: two home-made vertical seismometers

Hi Kareem
  This maybe a little to involved but I made a long period horizontal ( ~10"
long ) from information read from Sean Thomas Morrissey's web site I built the vertical
he described first then tried a horizontal next. It looks like the W.F.
Sprengnether figure at the "PSN info" location.It's natural period was about
5 sec without the feedback circuitry. I used his circuitry with his
description of the speaker coil and the VRDT construction for the feedback.
I think the period was increased to about 20-30 sec but I haven't been able
to check the base frequency vs response yet. the construction was not
expensive but it was time consuming. I chose the component values from his
Mcad equations but I'm not sure they are optimum (part of the required input
was the coil output G and the sensors natural frequency) . I'm still working
on a few bugs in the external amplifier/filter  and balancing motor
circuitry. It did record the recent Mozambique event but so did my simple
Lehman ( pretty large event). 
       I have wanted to try a horizontal lehman type sensor but with two
long springs (one on each side) meeting at a heavy weight and slightly apart
at the base of the boom. For a vertical like John Lahr showed previously, if
the spring angle is brought more horizontal (parallel with the boom ) my
understanding is the period is increased. I thought the same might apply
with the horizontal  and one would not have to worry as much about the drift
the Lehman can produce as the boom assemble approaches the non returning
position ( ie trying to increase the lehman period). 
Sorry I got so wordy

Kareem at HeyJooJoo  wrote:

	Hi Steve,
	Are there any simple plans for building a horizontal, long period
	seismograph? (I know that there are tons of places online but
figured you or
	the others may know of some real-time plans.)
	-----Original Message-----
	From: psn-l-request@..............
[mailto:psn-l-request@............... On
	Behalf Of Steve Hammond
	Sent: Wednesday, February 22, 2006 9:02 AM
	To: psn-l@............... PSN-L@..............
	Subject: RE: two home-made vertical seismometers
	If you want to build a simple seismograph, here is a URL of a very
	vertical seismograph that was designed by a fellow in Pasadena in
the early
	It uses a screen door spring and cost under $20. It is made from
	parts in a local hardware store and produces good results. It does
lack the
	electronics however, so if you check the same site,
	you will find a pre-amp using OP-07's that can be used with this.
The coil
	can be built from #44 wire on a plastic frame. You can get the frame
	Radio Shack if you just purchase a spool of their red/black/green
	construction wire. Hand wind about 4,000 turns of the #44 wire onto
a frame.
	Warp the coil in black electrical tape to protect it. The magnet is
a cow
	magnet sold in an animal feed stores but other magnets will also
work. I
	used these plans to build a system for a 5th grade classroom and the
	students were able to locate local events with it.
	Regards, Steve Hammond PSN San Jose, Aptos California
	-----Original Message-----
	From: psn-l-request@..............
	[mailto:psn-l-request@................. Behalf Of Gerencher, Joseph
	Sent: Tuesday, February 21, 2006 12:09 PM
	To: PSN-L@..............
	Subject: two home-made vertical seismometers
	I have photographs of two vertical seismometers that were made by
	Jim Lehman and given to me. Both have been in continuous operation
	several years and both have a natural period of about one second.
	smaller unit is in my classroom and the larger one is in the
	beneath the classroom. I modified the damping of the smaller unit
	copper plumbing fittings, which makes it both easier to construct
and easier
	to operate than the larger one. The web address for going directly
to the
	photographs is too long to post on an e-mail, so if you want to see
	of both these seismometers go to my opening web page at
	then click "homemade seismographs," click "Illustrated history of
	the seismometer system, 1991 to 1998" and click the links on that
	Additional detailed photographs of the construction design of the
	home-made seismometer can be found at the following web site: Unfortunately, I
have not
	yet gotten around to annotating these photographs, but intend to do
so in
	the next several days.
	Joe Gerencher
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