{"id":14,"date":"2012-04-09T15:26:56","date_gmt":"2012-04-09T15:26:56","guid":{"rendered":"http:\/\/nf3v.com\/blog\/?page_id=14"},"modified":"2012-06-27T01:57:39","modified_gmt":"2012-06-27T01:57:39","slug":"seismology","status":"publish","type":"page","link":"http:\/\/nf3v.com\/wp\/?page_id=14","title":{"rendered":"Lehman Seismometer"},"content":{"rendered":"

I settled on a Lehman design for my first seismometer.\u00a0 It is now installed in a crawl space in the house in a N-S direction so that it may best pick up activity from an east-west direction.<\/p>\n

With my design, almost everything can be picked up with one trip to a Home Depot \/ Sears Hardware \/ Lowes circuit.\u00a0<\/address>\n
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Here you see the general overview.\u00a0 (2) 18″ sections of 1\/2″ pipe, (2) 24″ sections and (1) 5″ section.\u00a0 There are also (4) 90 degree elbows.\u00a0 There are 2 sections of angle iron on the upright and (2) sections of 1″ x 1\/4″ cold-rolled steel for the bases.\u00a0 Some have used flanges for the uprights, mounted on a metal base.\u00a0 Unfortunately, the largest base I could find was 12″ x 12″ x 1\/4″ steel, unless I ordered it from a metal supplier.\u00a0 My goal was to make something that could be easily copied if needed.<\/address>\n
I have also installed pieces of 1″ angle diagonally to prevent flexion of the system.<\/address>\n
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One of the most difficult components to find was the weight.\u00a0 Everyone else uses lead melted into a can.\u00a0 Years ago I had found (by luck) 5 pounds of lead at the hardware store.\u00a0 But, the thought of trying to melt it and getting lead poisoning scared me.\u00a0 So, I sacrificed a 5 lb hand weight instead – instant gratification, no toxicity…what more could you ask for.\u00a0 O, and BTW – the lead cost me $15, the weight was marked at $3.\u00a0 The tape on the far side is for some extra weight as I was not exactly precise in my drilling and it is somewhat off balance.<\/address>\n
UPDATE:\u00a0 The weight was a good idea, but there was a lot of noise.\u00a0 Advice…go with the lead!\u00a0 As a source, go to a fishing shop and get some lead weights.\u00a0 It was easy to melt the lead with a propane torch (much easier than I thought) \u00a0If you go this route, it might be wise to offset the hole through which the boom goes through.\u00a0 That way, there is less rotational rocking of the boom.<\/address>\n
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Here is the damping system – a U-bolt (for wire cable, I think 1\/4″, just make sure it fits the boom.\u00a0 For me, I used a 3\/8″ boom) and 2 angle and brass stock (I think you could use the brass plate for the bottom of doors).\u00a0 The tupperware is now partially filled with 10W-30 oil.\u00a0 Just another instance of kitchen-ware being sacrificed to the gods of scientific investigation.<\/address>\n
The magnet stays there of it’s own accord.\u00a0 Some have glued it in place.\u00a0 I guess we’ll see if it stands the test of time.<\/address>\n
UPDATE:\u00a0 I have now gone with a magnetic damping system.\u00a0 The oil was a PITA (pain in the …) and my crawl space now has a nice stain.\u00a0 Additionally, I was concerned with temperature changing the viscosity.\u00a0 Advice…go with the magnetic system.\u00a0<\/address>\n
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The boom rests on a 1\/4″ steel ball bearing, which in turn rests on a polished 3\/8″ bolt.\u00a0 It’s the gold-looking kind in Sears Hardware.\u00a0 I think that it is some type of alloy.\u00a0 Anyway, it’s polished to a mirror finish with a dremel tool.\u00a0<\/address>\n
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UPDATE:\u00a0 It was pointed out to me that the ball bearing actually should be on the mount and the polished bolt on the boom.\u00a0 This way, the actual point of contact remains fixed in relation to the mount.<\/address>\n
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The top is the same way, ball bearing on a polished bolt head.\u00a0 I do not take credit for this design, as I copied it from John Cole.\u00a0\u00a0I have noticed that the ball bearings can slip on the polished surface of the bolt heads.\u00a0 I’ll wait and see if it becomes a problem.\u00a0 John Cole states that he has not had any problems.<\/address>\n
UPDATE: My boom did in fact have problems with slipping downward.\u00a0 I believe that is was because the boom was heavier on the long side from the balance point at the weight.\u00a0 Advice…boom should be balanced.<\/address>\n
The one thing that is missing from the design is some type of stabilizer – something to complete the hypotenuse of the triangle.\u00a0 I can see that vibrations up and down could be a problem.\u00a0 This can also be taken care of with a horizontal damper. (Note: see top of page regarding the stabilizing angle pieces.)<\/address>\n
The entire apparatus is encased in a box made of 1″ Styrofoam to reduce the effects of air currents.<\/address>\n
Currently, I have achieved a period of 19 seconds.\u00a0 I hope that will be enough.<\/address>\n

The electronics for the project were purchased from\u00a0Larry Cochrane<\/a>\u00a0at the Redwood City Public Seismic Network. Larry is very helpful and although they were not inexpensive, they make the process much easier to set up.\u00a0 He uses his own program called WinSDR to record the A\/D signal.\u00a0 This program interfaces well with his other program WinQuake, which is used to analyze the data<\/p>\n

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Update (late 2007) – The Lehman is offline at present. The output from the coil is nill and I haven’t had the time to get into the crawlspace and figure out what is wrong. I will post if there is any change.<\/address>\n
Update (2012) – The Lehman is truly offline at present. I’m making arrangements to have it donated to a local college for their geology program. \u00a0It was a\u00a0wonderful\u00a0experience for me to build and I hope that it excites future geologists.\u00a0<\/address>\n
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I settled on a Lehman design for my first seismometer.\u00a0 It is now installed in a crawl space in the house in a N-S direction so that it may best pick up activity from an east-west direction. With my design, … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/pages\/14"}],"collection":[{"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14"}],"version-history":[{"count":28,"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/pages\/14\/revisions"}],"predecessor-version":[{"id":259,"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=\/wp\/v2\/pages\/14\/revisions\/259"}],"wp:attachment":[{"href":"http:\/\/nf3v.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}