PSN-L Email List Message

Subject: Seismographs for students
From: Ruediger Wisskirchen rwisskirchen@.......
Date: Sun, 02 Jan 2000 23:43:34 +0200

barry lotz wrote:

> Ruediger
>     It may work as a strong motion sensor. I agree with Ted, usually you want
> the natural period of the sensor to be longer than the lowest period you want
> to record. Also since the output would be a function of the # of wire coils
> turns you may have a very low output signal . Speakers usually have few turns.

But is it possible, that the strong magnet more than compensats this
A simple test with a big loudspeaker, a simple amplifier with a 741 and
100 gives a strong signal, when I just make a bit wind with my hand
against the

> What you describe maybe the begining of a force balance sensor but you would
> need a displacement sensor included which would complicate matters.

I have read the article about the force-balance-seismometer, but due to
my oor
english I haven`t quite understood the difference between the
forcebalance and the
Why do you need a displacement sensor?

> Do you have
> access to magnet wire and simple rectangular magnets? You could use an electric
> drill and wind your own coil of  1000+ turns on say a old spool like an empty
> solder spool.

Is it better for a high voltage to have a short coil with much layers or
does a
long coil with the same number of wires produeces the same effect?

> You could then put a rectangular magnet on both sides of the
> coil. As Ted says you probable will have more interesting events if you do not
> attach the groung to the end of the boom except as I have described above. I
> hope this helps a little.  Most of us look around  to find possible sensor
> parts from devices use for other things, for example computer harddrive driver
> as sensor/coil pairs.

I still have some old harddisks, thanks for that hint.

> Barry
> ted@.......... wrote:
Thanks Ruediger Wisskirchen (rwisskirchen@........


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Larry Cochrane <cochrane@..............>