On 11/9/2012 6:30 AM, Bob Smither wrote:
>
> On Fri, 2012-11-09 at 06:10 -0800, GMVoeth GM wrote:
>> Hello PSN,
>>
>> I know with a velocity sensor the voltage increases with frequency after
>> F0 if given the same
>> vertical motion amplitude. This seems to be because as the frequency
>> increases
>> so does the velocity and thus, the voltage output.
>>
>> This means to me the energy also increases as the square of the velocity.
>> So like, double the velocity, quadruple the energy.
>>
>> What i would like to do is: filter at f0 (1.0Hz) so that given
>> a steady shake amplitude (sine wave) but incresing frequency
>> that the voltage will remain constant.
>>
>> Now I understand this may not be possible.
>
> I think it is.  A simple RC low pass filter (R from signal to C, C to
> ground, output at junction of R and C) gives:
>
>    T(S) = 1 / (R*C*S + 1)
>
> Above w = 1/(R*C) this is
>
>    T(S) ~ 1 / (R*C*S)
>
> exactly what you need to reduce gain proportional to frequency.
>
> For your example, w = 2*pi*1Hz = 1/RC so C = 1ufd, R = 160K should work.
>

I find this interesting.

I have eliminated filters except for a single HPF n=1 at like 100seconds
and am looking at pure noise.

At 8AM MST today I get occasional over driving (jamming) of my
preamplifier with no filtering.

I need this level of amplification to see the smaller seismic signals.

If I apply n=2 LPF at 1.0Hz using winquake I get the best flattening
of the noise baseline above 1.0Hz. Noise is human vehicular related.

It is an absolute must for me to apply n=2 at 1.0 Hz to prevent
jamming by vehicular and other noise.

Does this mean there is a problem with my geophone
or is vehicular noise increasing with frequency like n=1
to add to the velocity profile of the geophone ?

None of this is speaking of Alizing problems.

this is an extremely noisy town for vehicular activity.
(Apache Junction AZ USA)

Would it be best to stop recording during the day
or best to heavily filter to keep the system from being
jammed. Heavy filtering terribly affects the resulting
waveforms ?

Regards,
geoff




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