PSN-L Email List Message

Subject: Re: New Seismo
From: Bob McClure bobmcclure90@.........
Date: Mon, 25 Jul 2011 18:06:17 -0400


Hi Dave,

  What possible advantage do you think you are getting from all that weight?
The only possible benefit that I can imagine is that the sensor becomes less
sensitive to air drafts. There are disadvantages, such as more difficulty in
obtaining adequate electromagnetic damping, deformation of the pivots, and
flexure of the support frame.

  My horizontal sensors have only an added weight of 100 grams of lead
solder. My coil and magnet design provide enough output, so shunt damping is
easy. A load of ~50K provides the proper damping. I do not need any separate
damping vane and magnet.

  Old sensors had heavy weights because they had to drive mechanical
linkages, or galvanometers. Modern electronic amplifiers eliminate the need
for heavy pendulums.

Bob

On Mon, Jul 25, 2011 at 5:41 PM, Dave Nelson wrote:

> Hi Randy,
>                ahhh now there's some words of wisdom that I hadnt thought
> about
> before. hmmm but the balance point would be probably right at the weights.
> The other seismo's I have seen online  Chris C's one that I have sorta
> copied,
> the SEP, and others, the support wires have been some distance back from
> the
> weights.   Out of curiosity how much weight do you have on your one ?
> what are other guys using ?   Gosh I was thinking 4 pounds was nowhere near
>
> enough and would have preferred almost twice that amount.  Thats
> considering the
>  Sprengnether I had in NZ had ~28 lbs os mass.
>
> All that being said I could still take the support wires to the other end
> of the frame
> holding the coil magnets and gain a bit more ib the balancing act  :)
>
> speak up all   what weights are commonly being used ? and how many of you
> considered the balance point of the boom when adding the support wires ?
>
> cheers
> Dave
>
>
> At 12:17 AM 26/07/2011, you wrote:
>
> Hi Dave,
> If you remove the boom and find the balance point of the boom you can
> re-attach the support wire at or very near that point.  This will remove the
> vertical force on the pivot and allow it to sit in place.  Another option
> would be to remove one weight.  Removing the weight would also help to
> increase the damping effect.  With 4 pounds of weight in my experience you
> will not get enough damping with the 1 small magnet.
> Randall L. Pratt
>
>
Hi Dave,

= =A0 What possible advantage do you think you are getting from all that weig= ht? The only possible benefit that I can imagine is that the sensor becomes= less sensitive to air drafts. There are disadvantages, such as more diffic= ulty in obtaining adequate electromagnetic damping, deformation of the pivo= ts, and flexure of the support frame.

=A0 My horizontal sensors have only an added weight of 100 grams of lea= d solder. My coil and magnet design provide enough output, so shunt damping= is easy. A load of ~50K provides the proper damping. I do not need any sep= arate damping vane and magnet.

=A0 Old sensors had heavy weights because they had to drive mechanical = linkages, or galvanometers. Modern electronic amplifiers eliminate the need= for heavy pendulums.

Bob

On Mon, Jul 25, 2011 at 5:41 PM, Dave Nelson <dave.nelson@...............>= wrote:
Hi Randy,
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ahhh now there's some words of wisdom that I hadnt thought about
before. hmmm but the balance point would be probably right at the weights.
The other seismo's I have seen online=A0 Chris C's one that I have sorta copied,
the SEP, and others, the support wires have been some distance back from the
weights.=A0=A0 Out of curiosity how much weight do you have on your one ?
what are other guys using ?=A0=A0 Gosh I was thinking 4 pounds was nowhere near
enough and would have preferred almost twice that amount.=A0 Thats considering the
=A0Sprengnether I had in NZ had ~28 lbs os mass.

All that being said I could still take the support wires to the other end of the frame
holding the coil magnets and gain a bit more ib the balancing act=A0 :)

speak up all=A0=A0 what weights are commonly being used ? and how many of you
considered the balance point of the boom when adding the support wires ?

cheers
Dave


At 12:17 AM 26/07/2011, you wrote:
Hi Dave,
If you remove the boom and find the balance point of the boom you can re-attach the support wire at or very near that point.=A0 This will remove the vertical force on the pivot and allow it to sit in place.=A0 Another option would be to remove one weight.=A0 Removing the weight would also help to increase the damping effect.=A0 With 4 pounds of weight in my experience you will not get enough damping with the 1 small magnet.=A0
Randall L. Pratt


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