Hi Chris,

It would be quite possible to use a different model.  Spice can 
handle most anything.  I chose the model I did because that is what 
was used in the reference I found, and also because it made it easy 
to apply a velocity input to the model, i.e., a voltage.

For noise analysis, I can easily model an acceleration input by 
integrating the voltage representing the acceleration to make it into 
a velocity, and then connecting that to the accelerometer model's 
velocity input.

Indeed, the model shows a +1 slope in the velocity response (flat to 
acceleration) from about 0.65Hz to around 50Hz.  The electronics 
integrates that to get a flat velocity response over that frequency range.

In the geophone model, Ceqv is an analog for the mass, Leqv 
represents the support spring and Reqv, the open-circuit 
damping.  The coil parameters, Lc and Rc are the actual, measurable, 
values for the coil inductance (mass fixed) and resistance.  There is 
also a small coil shunt capacitance which is insignificant, which was 
ignored.  Fixing the mass by inverting the geophone causes the 
support spring to appear to be infinitely stiff, causing Leqv to 
become zero, thus allowing Lc to be measured.

It is interesting to note that only a modest amount of negative 
resistance, about -87 Ohms, is required to get this particular 
geophone's corner down from 0.65 to 0.5 Hz.  You could do nearly as 
well letting it drive an ordinary zero input impedance current amplifier.

Regards,
Brett


At 08:44 AM 10/7/2012, you wrote:
>From: Brett Nordgren 
>To: psnlist 
>Sent: Sun, 7 Oct 2012 3:37
>Subject: Geophone electrical model
>
>
>Hi all,
>
>I just finished up documenting a mechanical-analog electrical model
>for geophones.  It can be incorporated in a circuit simulation
>program such as Spice, and allows you to look at the overall system
>performance with respect to a ground velocity excitation.
>It includes an Excel workbook for computing the analog equivalent
>component values from the geophone spec. sheet, and includes some examples.
>http://bnordgren.org/seismo/GeophoneModel.zip
>
>
>Hi Brett,
>
>
>     Do you have a current generator analogue for this circuit, 
> please, or can Spice
>
>only use voltage generator circuits ?
>
>
>     I am a bit puzzled by the inclusion of the SERIES coupling 
> capacitor, Ceqv. How
>
>does this arise, please ?
>
>     The Lippmann circuit gives a first order increasing output with 
> frequency fn(f).
>
>
>
>     Regards,
>
>
>
>     Chris Chapman
>
>
>
>


__________________________________________________________

Public Seismic Network Mailing List (PSNLIST)

To leave this list email PSNLIST-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.