PSN-L Email List Message

Subject: Re: Seismometer Questions
From: "Jim and Connie Lehman" lehmancj@...........
Date: Wed, 2 Jun 2010 17:17:58 -0400


Jeff--greetings from Virginia:

I looked at your pics on the site, and will make the following suggestions--

The way you have your pickup magnet--hanging DOWN makes for vertical 
motion pickup.  Turn and counter balance as necessary the magnet 90 degrees 
for horizontal pickup-

Make a coil of 3 in dia AND INTRODUCE ONLY 1/2 OF THE COIL IN THE STRONG 
MAGNETIC POLES.  Your pics show a small size relay coil ---pretty well the 
whole thing in the magnetic field.  Your net output  is down or minimal. 
Making a good 3 in. coil of 5000 turns at least is challenging--#30, 32, 34 
wire--size is not critical--as you found, #40 is too small and tears 
easily!!!

As Larry says, do away with wood mounting, expecially for the coil.  The 
wood mount for the damping system is probably ok.

Try for 15 sec at least for the period of swing ---longer if possible-

Overall your system is coming along, but with your design, you want to 
accent the HORIZONTAL motion.  Best wishes in your seismic interests.

Jim Lehman
----- Original Message ----- 
From: 
To: 
Sent: Sunday, May 30, 2010 1:20 AM
Subject: Seismometer Questions


> Hello everyone,
>
> I am new to this hobby of seismology. After trying for years (I get 
> sidetracked a lot) to make a
> seismometer (or is it seismograph???), I finally got it finished. I have 
> made a Lehman
> horizontal seismometer. I am using WinSDR and WinQuake. I am using a Larry 
> Cochrane
> 16bit A/D converter and his amp/filter board. I have a GPS receiver (Mr. 
> Cochrane's too) for
> timing.
>
> I have photos of everything I will refer to at:
>
> www.flickr.com/photos/darksky123/
>
> I changed a few things. I thought it would be very difficult for me to 
> made a perfect knife edge
> for the pivot point so I epoxyed a ball bearing to the end of my steel 
> rod. I sanded smooth the
> surface that it rests on, (not sure what it is called). Seems to work???
>
> For my pickup magnet, I hung it down off the rod. I could not get it to 
> hang properly when I
> tried it on the side of the rod. Made things twist.
>
> I got a bolt for the thing that the wire attaches to on the top piece. To 
> vary the period of the
> arm, I just adjusted the length of the bolt.
>
> So my question. I read that I should be able to detect magnitude 6 and 
> greater for earthquake
> around the world. For a while after I got things running, there were no 
> large quakes. The first
> large one was the 7.2 Baja Claifornia quake on Easter Sunday. I got a 
> great record of it
> (I was pretty much bouncing off the walls when I saw it). I have a photo 
> of the computer
> monitor and of the Winquake output. Since then I have not detected much of 
> anything. What
> really prompted me to write was not detecting the Vanuatu 7.2 quake from 
> last week. I got a
> small squiggle, but not enough to put WinSDR into alarm and the time was a 
> couple of
> minutes early from when the waves should have arrived according to the 
> USGS. Compared
> to what I got with the Baja quake, I thought I should have gotten 
> something. I realize it is a lot
> further away, but I look at outputs that are posted on Infiltec's website 
> of amateur recordings
> and some people get great recordings of a lot of earthquakes and I get 
> nothing. I am hoping
> the people here that are much more knowledgeable than I am will be able to 
> point out
> improvements or mistakes that I am making.
>
> For my pick up coil, I originally had a coil from a relay. It was about an 
> inch in diameter. It
> seemed to work for starting out. That was the pickup coil I was using when 
> I got the Baja
> quake. I knew I had to get one with more turns of wire and a higher 
> resistance, that one was
> only about 300 ohms. A local electronics shop had some 40AWG magnet wire, 
> a 1/4 pound
> roll. I bought it and made a thing to roll it onto. I got about 1/3 of the 
> way through and there
> was a break in the wire on the spool! I tried to join it together as best 
> as I could, but 40 AWG
> wire is pretty small and hard to work with. It worked for a bit, but as I 
> worked on a mount for
> the spool, the coil opened up. Not really feeling like playing with that 
> tiny wire again, I looked
> through an electronics supply catalogue and found a 110Vac power relay 
> that stated a coil
> resistance of 11K ohms. I bought it and in fact it has about 10.8 K ohms. 
> I took the relay
> apart and got just the coil. The question I have about it is, does size 
> matter? The coil itself is
> only about 1/2' in diameter. I look at other amatuer seismometers that I 
> can find photos for
> and the coils are a lot larger. Should I get some larger gauge wire 
> (36AWG?) and make a
> new coil? Or is the coil I have now OK? I only have it secured to a small 
> piece of scrap 2x4
> now. If the coil is Ok I will build a better mount for it.
>
> I believe the seismometer works. When I walk up to it, WinSDR shows 
> movement and it
> usually goes into alarm unless I walk up very slowly. I have a road 
> construction site very
> close to my house. The trace is very noisey during the day when the 
> construction is going on.
> But in the eveings and at night, (See one of my photos you can see the 
> trace go quiet at 7:00
> p.m. when the construction shuts down for the night), the line gets a lot 
> smaller. I can also tell
> when it is windy outside, by the output of my seiesmometer. I can also see 
> a larger trace with
> the new coil inplace. So I think that the new coil did make an improvement 
> in my system.
>
> The period of my system is about ten seconds. That is about as long as I 
> am able to get it. I
> can't seem to get the 14+ I read about for some systems. Should I fight 
> with it to get a longer
> period, or is ten seconds long enough?
>
> Is a ball bearing Ok for a pivot point?
>
> I sent a letter and photos to Mr. Cochrane and he told me to get rid of 
> the wood I was using
> on my system. I had made a mount for the pick up coil magnet out of wood 
> at first (it is now
> metal). It is easier for me to work with wood than metal. I have the 
> copper plate for my
> dampening attached to the rod with a piece of wood. Is this OK? The 
> original diagram I was
> working with says use wood. Should I get rid of it too and use metal?
>
> I have my seismometer orientated basically north-south. Is that Ok for 
> North America or
> shoud I point it east-west?
>
> Should I be getting more earthquakes. Or for where I live, are things 
> working as best as I can
> expect?
>
> I hope someone out there will be able to help me out and answer my 
> questions. I have found
> in the past that if you are having a problem with a project, most likely 
> someone out there had
> the same problem. Get with a group of people that have the same interests 
> and you most
> likely will be able to get an answer. I am hoping that this will be the 
> case.
>
> I am looking forward to my new hobby of seismology. If things work well I 
> hope to make
> another one for the other direction and maybe even a verticle seismometer. 
> I bought a three
> channel amp from Mr. Cochrane. Just in case... :-)
>
> Thanks for all your time. Kind of a long letter...
>
> Jeff Zambory
> Calgary, Alberta
> jzambory@.........
>
>
>
>
>
>
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