PSN-L Email List Message

Subject: Re: Geophone Generator Constant, Winquake
From: Geoffrey gmvoeth@...........
Date: Tue, 14 Jun 2011 21:34:49 -0700

Hello Chris,

I sent that info in quite some time ago.

It is based upon an overdamped system where
a portion of the up slope (dc to f0) of an overdamped 
geophone becomes n=1 between two points
and you simply need to use an n=1 LPF at
the lower frequency on the output,
to obtain an overall velocity response.
within these two limits.

But now I am no longer using that same circuit.

I have gone to a three opamp instrumentation circuit.

I like what i am seeing at the moment.

but i am using butterworth damping and not overdamping.

The plus inputs are tied to ground
and the geophone rests between the
two negative inputs where normally
Rg (gain resistor) is located.

I figure if I can get an h=3 for damping
that I can also get 6 seconds to 6 hertz
frequency band which is all velocity.

I also figure this to be possible
with no damping resistor in the just
described circuit.

The op amp becomes the current sink
in this design, like a direct short
somehow developing a voltage
internal to the opamp depending upon the
current and not the voltage from the
geophone within the opamps directly connected
to the geophone.

But in the final third amplifier you should
be able to provide a single stage LPF
at the lower frequency of 1/6 to get the
velocity profile of 1/6 to 6 hz.

suitable for regional events.

This rolloff could hypothetically be at
30 seconds instead of 6
allowing one to see those surfave waves.
even if they are not in velocity form.

Dont know what else to say except
you are a lot like those newsgroup people
who never directly approach my questions.
They go off on a tangent which gives me a
nonesense answer.

I am not questioning your ability as an engineer,
Im just looking for direct answers to direct questions
without personal feelings getting into the data itself.

i do like to know you are human and not a machine.

Are you trying to tell me all this stuff i see on the internet
about overdamping is for the birds ?
That you are the only expert who knows this stuff ?
and that overdamping will simply not work?

The changes I make are relatively fast.
Todays circuit may not be yesterdays
even though they all might originate
in the 1950s.

BTW, my internet connection has been terrible
ever since media com has been taken over
to private owners (stock holders with majority powers ?)
I do not know whats really going on,
just I will go hours with no connection and
no decent explanation why no connection.
i feel under personal attack and no one to turn to for serious help.

Best Regards,

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