PSN-L Email List Message

Subject: Re: meter movements as geophones
From: meredithlamb meredithlamb@.............
Date: Thu, 26 Jun 2003 22:38:58 -0600


Hi all,

Suspect that the "natural" period would be rather short with rather
a severe limited mass weight of course....but....one might see
some of the longer period waves from the bigger quakes.
Would suspect that the older (1960's-1970's) (big) meters with
4 extending base mount screws would be the handiest to
convert/utilize.  I think this type of meter suspension is also called
a "taut band"....not that it really matters....but interesting with the
variety of names it comes under....as does alot of material.

Would also guess that any circuit might need some adequate
isolation from the meter.....if I'am putting it right.

Theres actually another alternative rather than just amplifying
the meter coil output.  One could use the meter coil and a
suitable potentiometer....just for dampening.  One could use
light and two photocells around the end of the meter pointer
(boom/mass) and likely see truer displacement longer periods
than the original velocity meter coil/magnet output.

I even wonder if the meter coil could be a nice feedback
mechanism with a light output approach.  Don't ask me how
though....ha.

One would likely need a fine and gental mechanical touch
to do this I'am sure....probably the toughest aspect of all.

Take care, Meredith

ChrisAtUpw@....... wrote:

> Hi there Jim,
>
>      If you can get hold of a 50 or 100 micro amp panel meter with a
> torsion ribbon suspension (not a pivot) and mount it with the needle
> vertical, you can then glue a small bit of metal onto the end of the
> needle and it will act as a small seismic sensor. Meters with pivot
> suspensions generally have too much friction to be reliable.
>      If you make the added mass out of thin Al sheet, you can then
> damp the motion more using magnets, if need be. The meter movements
> themselves are usually designed to be overdamped, but adding more mass
> to the end of the neede is likely to allow them to oscillate.
>
>      Regards,
>
>      Chris Chapman


Hi all,

Suspect that the "natural" period would be rather short with rather
a severe limited mass weight of course....but....one might see
some of the longer period waves from the bigger quakes.
Would suspect that the older (1960's-1970's) (big) meters with
4 extending base mount screws would be the handiest to
convert/utilize.  I think this type of meter suspension is also called
a "taut band"....not that it really matters....but interesting with the
variety of names it comes under....as does alot of material.

Would also guess that any circuit might need some adequate
isolation from the meter.....if I'am putting it right.

Theres actually another alternative rather than just amplifying
the meter coil output.  One could use the meter coil and a
suitable potentiometer....just for dampening.  One could use
light and two photocells around the end of the meter pointer
(boom/mass) and likely see truer displacement longer periods
than the original velocity meter coil/magnet output.

I even wonder if the meter coil could be a nice feedback
mechanism with a light output approach.  Don't ask me how
though....ha.

One would likely need a fine and gental mechanical touch
to do this I'am sure....probably the toughest aspect of all.

Take care, Meredith

ChrisAtUpw@....... wrote:

Hi there Jim,

     If you can get hold of a 50 or 100 micro amp panel meter with a torsion ribbon suspension (not a pivot) and mount it with the needle vertical, you can then glue a small bit of metal onto the end of the needle and it will act as a small seismic sensor. Meters with pivot suspensions generally have too much friction to be reliable.
     If you make the added mass out of thin Al sheet, you can then damp the motion more using magnets, if need be. The meter movements themselves are usually designed to be overdamped, but adding more mass to the end of the neede is likely to allow them to oscillate.

     Regards,

     Chris Chapman


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