PSN-L Email List Message

Subject: Re: Geophone Generator Constant, Winquake
From: Mauro Mariotti mariotti@.........
Date: Sat, 28 May 2011 09:39:20 +0200


Hello Geoff,

i didn't checked all the numbers but you are right.
In seismology all the recording are made in counts; in some cases in 
volts. After recording all is deconvolved to the final measurement unit 
applying the inverse filter of the system transfer function also called 
"system response".
In this way the amplitude at all frequencies is corrected appropriately.
If you go to the web site of my company www.sara.pg.it
and download the software SEISMOWIN using the SEISMOWIN.MSI you can 
install a number of tools.
After installed SEISMOWIN.MSI launch it and a window with many icons 
will show up.
No modules are installed at this moment.
You need to install what you want.
Clicking with the right-button of the mouse you open some options, among 
them you select "install from internet".
Clicking with the left-button of the mouse you launch the module.
In your case i recomend to install the RESP module.

This module allow you to compute the transfer function of practically 
any system. You can export the system response in poles and zeroes or in 
a frequency/amplitude/phase table.
The table or the poles-and-zeros can be normalized at any frequency 
(1Hz, 10Hz or whatever).

I would launch to Larry the idea to implement this correction in 
WinQuake instead of use only the transduction factor wich is valid only 
in the portion of band where the system response is flat.
At moment we can use the transfer function in the module SURVEY, its use 
need a little training.
We have some manual online downloadable in the same manner of the module 
installation.
You may try.

Use of SEISMOWIN sofwtare is free for educational or private use.

best regards
Mauro




Il 27/05/2011 23:34, Geoffrey ha scritto:
> Hello PSN,
>
> Question: Does any/all of this seem right or wrong to you ?
>
> The layout of the circuits are as follows:
> 1. Geophone Preamplifier and Damping circuits X500 no filtering
> 2. Equalization Filter and amplifier X21 filter at (1/18.8) Hz
> 3. Antialize filter X1 N=8 at 10Hz
> 4. DC blocker X1 N=1 at (1/100)Hz
> 5. Voltage Follower X1
> 6. Distribution Manifold circuit
> A. A/D converter X1
> B. Analog Meter circuit X20
> Hs10-1 Vertcal Geophone
> 435 ohms at operational temperature
> G = 2.99 V/(in/sec)
> hm = 0.35
> Fc = 1Hz
> Mass = 33 ounces avd.
>
> Given:
> Generator Constant:
> 2.99V/(in/sec)
> Geophone resistance:
> 435 ohms
> Damping resistor = 205 Ohms
> Preamplifier with gain of 500 and no filtering
> Preamplifier Low Pass Filter N=1 of the following
> Rf = 1 Meg
> Cf = 3uf
> gain is X21
> When I Plug in my numbers,
> The OVERALL amplifier gain was computed
> only for 1 Hz.
>
> 1. minus Voltage loss related to damping resistor
>
> K1 = 20 log(Rd/(Rg + Rd))
> = -9.888 dbv
>
> 2. plus DC voltage gain of preamplifier (no filtering)
>
> K2 = 20log((R1 + R2) / R1)
> = 53.979
>
> 3. plus DC voltage gain of filter stage
>
> K3 = 20log((R1 + R2) / R1)
> =26.510
>
> 4. minus voltage gain due to filtering at at 1Hz
> K4 = 20log(Xc/Z)
> =-25.518
> Xc = 1/2PiFC
> Z = SQR(r^2 + Xc^2)
>
> 5. Overall:
> K = K1 + K2 + K3 + K4
> = -9.888 + 53.979 + 26.510 + -25.518
> = 45.083dbv or X179.535 AT Only ONE HERTZ
>
> I do not worry about dampend generator constant
> ( Ge ) since it is covered under Item number one as a loss.
>
> This should mean that only at one hertz
> my Ge going into the 16 bit A/D is
> 2.99 X 179.535 or 536.80965 (Volts/(inch/second))
> This should translate to Volts/(cm/s) like this
> Ge = 536.80965 / 2.54 = 211.3423819 (Volts/(cm/sec))
> Going into the A/D converter which is Volts Per Count = (5Volts /
> 32767counts)
> This means One count is the following:
> 211.3423819 V/(cm/s) X (32767 Counts/ 5 Volts) = 13850.11166
> Counts/(cm/sec) or
> 1/13850.11166 (cm/sec)/COUNT or 7.220158E-6 (cm/sec)/count or
> *******************
> One Count equals 72.20158 nano meters per count At 1Hz and only 1Hz
>
> *******************
>
> This gain will have to be recalculated for any other frequency.
> I also have N=8 LPF at 10Hz and a N=1 100sec HPF Dc blocker.
> Does any of this sound right to you ?
>
> Is this the right way to calculate overall AMPLIFIER gain etc. for WinSDR ?
>
> What is the best way to handle the magnitude correction ?
> Like if no correction at all.
> It is my guess, by adjusting the generator constant
> because it might not meet factory specifications.
> All the other numbers seem to be known.
>
> Please do not challenge my damping resistor at this moment.
> I have chosen a value of 205 Ohms for my own selfish reasons.
>
> Regards,
> geoff
>
>
>
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>

-- 
Mauro Mariotti
http://www.infoeq.it
http://www.sara.pg.it

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