PSN-L Email List Message

Subject: Re: Damping Resistor
From: Geoffrey gmvoeth@.........
Date: Mon, 06 Feb 2012 18:19:48 +0000

The trouble with these government pubs is that
I do not have a decent reader for their
file types.
I will never understand why they don't use rich text files
or simply html or plain 7 bit text.
Something more universal than a snobby DOC file
which takes too much space on your machine
or cost too much money for the software to read it.
I do not like to MS stuff because they are too
involved when it comes to installing the software.
They almost always use special software
to make their documents.
I guess Ill stop crying now.


On 2/6/2012 5:39 AM, Stephen Hammond wrote:
> Hi Geoff, I get the impression you are looking for a simple answer to a
> complex problem. Here is a simple answer: I use three HS10 geophones on my
> system and based on word of mouth input I received from a USGS tech in 1990
> he told me to start with two  500 ohm resisters in a t-pad arrangement just
> to get started and work up until I got the output I desired. That said,
> Chris is right-- you will need the specs from the manufacture if you want to
> setup your geophones with any kind of precision . Here are two links, one to
> a USGS report describing setting the damping values for the S and T
> resisters in a t-pad style damping  (one resister across the coil output and
> one resister in series between the coil output and one of the inputs to the
> filter/amp).  Here is a link to a USGS paper and calibration results for
> their sensors.  
> Here is the link to the Stanford Geo lab calibration procedure for the L4C
> geophone.
> I hope this helps, Regards Steve Hammond PSN San Jose, Aptos, CA. 
> From: psnlist-request@.............. [mailto:psnlist-request@...............
> On Behalf Of chrisatupw@.......
> Sent: Sunday, February 05, 2012 4:42 PM
> To: psnlist@..............
> Subject: Re: Damping Resistor
> Subject: Damping Resistor
> Is anyone able to comment on this expression
> to get a value for the damping resistor ?
> .
> Hi Geoff,
>     Most geophones use a copper coil former, which also forms part of 
> the mass. Since this is moving in the magnetic field, damping currents 
> are induced in it, giving maybe 0.4 critical damping. I think that your 
> formula relates to a system with no inherent damping. The manufacturers 
> supply response curves for a range of damping resistors.  
>     Regards,
>     Chris


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