jonfr

jonfr
Magnitude:2

Joined: May 19, 2006
Posts: 93
Location: Hvammstangi, Iceland

Posted: Sun Jul 09, 2006 3:12 am

I think it is save for me to use 8 cm pipe. I will explain the fix for the magnet later on.

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Sun Jul 09, 2006 10:06 pm

Yes that will be fine .I was just doing the literal conversion from three inches

jonfr
Magnitude:2

Joined: May 19, 2006
Posts: 93
Location: Hvammstangi, Iceland

Posted: Fri Aug 04, 2006 7:00 am

I have added one more edit to the PVC seismometer. I have got rid of the concreate. I can use other element as base (metal) for the seismometer.

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Fri Aug 04, 2006 11:34 pm

Sure that should work fine .I used concrete because I was going to bury it and it is cheap.
When you get far enough along post some picture of your progress . I would be very interested in following your progress

Best as always
Terry

jonfr
Magnitude:2

Joined: May 19, 2006
Posts: 93
Location: Hvammstangi, Iceland

Posted: Tue Oct 03, 2006 2:16 am

Now I am finally ready to build this seismometer. I plan to use 4 cm magents, a resistior to have the signal as close to 1Hz as I can. What I don't at this moment is how long the rods needs to be. The base (the concrete) is problay going to be 10x15 cm (wide x hight).

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Tue Oct 03, 2006 2:46 am

The length of the rod I used was 10 inches or 254 mm and the diameter is .062 in or 1.5748 mm. With the weight of the floater magnet being changed I think the period will be change also.

Cheers
Terry

jonfr
Magnitude:2

Joined: May 19, 2006
Posts: 93
Location: Hvammstangi, Iceland

Posted: Tue Oct 03, 2006 6:27 am

You did use a really long rod. I've have to figure out few things in regards to that. But I don't think it is nessary to have this long rod. But I might be wrong.

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Wed Oct 04, 2006 9:59 pm

In theory the longer the rod the lower the frequency . Also the reason I used an antenna was because it had a coil at the bottom which made it very nimble.

Cheers
Terry

ve3sjk
Magnitude:1

Joined: Oct 12, 2006
Posts: 3

Posted: Thu Oct 19, 2006 11:01 am

Hi All,

I am working on building one of these units myself, i have most of the parts but finding the cel phone ant is slowing me down. Is the one you used metal ? I suspect that the coil your talking about at the bottom is giving the unit some mechanical damping that a straight rod will not. I could see putting some electrical damping in the unit 2 ways both would require feedback, 1 add damping magnets below the coils that are controlled with the feedback signal, or and forgive me if I am getting carried away but you could add a small stepper on the adjustable magnet at the top and have the feedback signal actually adjust the distance between the magnets. I used #36 magnet wire and the plastic spool from a roll of teflon plumbing tape. I used a small scale to get the proper resistance by measuring the wieght of the coil.

Here are the calculations

#36 awg - res per ft is 0.4148 ohms, weight is 0.0783 lbs/1000ft

To get 1100 ohms the length is aprox 2651.88 feet which when wound on the spool with have a wieght of (2651.88/1000)0.0783=0.207642204 lbs
This converts to 94.1849194 grams.

Regards
Steve

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Thu Oct 19, 2006 10:55 pm

Hi Steve and Welcome to the page. I am pleased to see that you are going to build one of these seismometers . So far I am very happy with the service that the one in this post has given. I agree that the cell phone antenna is a little difficult to find You are correct about the spring at the bottom it is critical to the design . The first designs I constructed I used various combinations of lengths ,weights, and different metals to come up with this design.

Currently I am working on another model .The main body is a small aluminum oxygen cylinder similar to what EMS services use. This one is slightly scaled up version with the antenna rod being approximately 2 feet long . With preliminary testing showing about a 2-3 second period . After a initial test period to get the feel of its response I hope to pull a vacuum in the cylinder to see how the response changes. I will start another post on that seismometer soon.

As for the damping you can make it as exotic as you what want . I like the stepper motor ideal but I think the actual movement of the motor would cause a lot of motion in the pendulum. In the PVC model There is an aluminum plate that holds the sensor coil that provides some damping with the rest coming from the top magnet. I think the main thing to remember is to make the pendulum very unstable with weight and then balance it with the top magnet .
Please post some picture of your progress on you seismometer .

Cheers
Terry K4gx

ve3sjk
Magnitude:1

Joined: Oct 12, 2006
Posts: 3

Posted: Tue Oct 24, 2006 10:59 am

Can you elaborate a little on the construction of the coil mount. I see the 3/16 au circle cut to 3" to fit inside the pipe but I get a little lost when you mentioned the 2.5 x 2.5 x 1/2 inche block that you bolted on top, is the coil sandwiched between a round 3" piece at the penulum end and a 2.5 by 2.5 by 1/2" thick block at the other end?

Terry
Site Admin

Joined: Apr 18, 2006
Posts: 109

Posted: Wed Oct 25, 2006 5:56 am