PSN-L Email List Message
From: "David H. Youden" dyouden@.............
Date: Wed, 30 Jun 2004 05:50:31 -0400
It looks good. THanks a lot for sharing the specs and the pictures with us.
Jason Brady wrote:
> Hi All,
> Finished building my first seismometer last weekend. It's the familiar
> Lehman design based on instructions, ideas and information from PSN and
> other resources on the 'Net. Several rather grainy pictures can be seen
> at http://home.comcast.net/~jr_brady/index.html (temp URL). Sorry about
> that; I really must purchase a better digital camera...
> The seismometer is built on a 12" x 36" solid aluminum base anchored to
> the concrete floor. 1" square hollow aluminum tubing forms the upright
> apparatus and supports. The boom is 1/2" square aluminum rod, 30" long,
> with a 5 pound lead mass. The pivot is a ball bearing/polished bolt
> combination. Guitar wire and turnbuckle forms the suspension. I
> wound the coil using almost 1 pound of #34 magnet wire. Coil impedance
> is 1.9K ohms. The magnet is standard Alnico bridge with 35-pound pull.
> Boom stops, component mounting brackets, etc. are formed from 1/2" flat
> aluminum stock 1/8" thick. Used brass hardware throughout.
> No damping yet in place. I'm fine-tuning the period and centering and
> want to give it some time to settle before damping. About a 15 second
> period seems to be the maximum obtainable thus far. Note the DIP socket
> mounted on a small piece of perfboard to the left of the BNC connector
> allow easy insertion of a resistor across the coil output. I also
> a copper vane for oil damping if the resistive approach doesn't work.
> made provision for mounting eddy current damping hardware (the beauty of
> working with soft metals like aluminum--easily cut, drilled, tapped).
> I attached the device to Larry Cochrane's Amplifier/Filter and ADC. The
> undamped sensitivity is amazing! Gently stepping across the floor a
> distance away sets the boom in motion. Will be interesting to see how
> responds to true seismic events once properly damped. I missed the
> Alaska quake, but being near the Juan de Fuca fault/subduction zone I
> to record a decent amount of activity.
> Any comments or suggestions on the design, construction, etc.?
> Jason Brady Lynnwood, WA USA
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