PSN-L Email List Message

Subject: Re: Signal To Noise Ratio of a Seismic Sensor
From: Dave Nelson davenn@...............
Date: Sun, 26 Mar 2006 08:34:01 +1000

Agree with you John,
      Ian,  as shown in your drawing 1/2 of your magnets are outside the 
coil area and only one side of the supporting bar.  This severely reduces 
the amount of voltage generated in the coils.

    As to Geoffery's questions,
             another good rule is ALWAYS use love noise components....

     Bi-FET Op-Amps     ....  eg  the  OPA 027  and  similar 
series,  rather 741   etc type

     Metal Film resistors  ... particularly are much lower noise producing than
                                        standard carbon resistors

    I have also always used coaxial cable for feedline between the sensor 
and the
   preamp board.  and for the short period geophones ... Bury them !   even 
6 inches below ground level cuts out a lot of stray RF field pickup and 
other electrical noise.


At 01:01 PM 25/03/2006 -0500, you wrote:

>ian wrote:
>>just to clarify what I said about magnets, I've drawn a simple sketch:
>You might crank the signal up a bit more by splitting that stack of 
>magnets in half, and clamping or gluing them on opposite sides of an iron 
>slug, with the magnets repelling each other at the attachment to the 
>slug.  The slug should sit in the center of the coil.
>The coil generates voltage in proportion to the flux that is passing 
>radially through the coil, and this arrangement crowds a lot more of the 
>flux in that direction.  It also makes the total magnetic field balanced, 
>so that the Earth's magnetic field cannot push or pull on the magnets as 
>it changes.  This reduces interference from things like solar storms.
>Your present design wasts a lot of flux that passes out the hole in the 
>coil and generates no signal.  Making the change I am suggesting might 
>double your signal while reducing some sources of interference and not 
>increasing resistive noise at all.

No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.1.385 / Virus Database: 268.3.1/292 - Release Date: 24/03/2006


Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]