PSN-L Message - Subject: Re: Robert's circuit and new WinQuake / WinSDR releases

On 2/13/2012 5:49 AM, chrisatupw@....... wrote: > > Larry Cochrane lcochrane@.............. > Sent: Tue, 7 Feb 2012 6:12 > Subject: Robert's circuit and new WinQuake / WinSDR releases > > Hi Everyone, > > In WinQuake the inverse filter can be found in the Time-Domain Filter > dialog box and in WinSDR the Channel Settings -> Integrate / Filter tab > dialog box. > > A few days ago there were some emails on the list regarding what numbers > to use for the pendulum frequency and high-pass filter. The pendulum > frequency is the undamped period of your sensor. *I had been working with this program about 4 weeks now. I am not satisfied with the results. Bob's self-standing program seems better. What participated my comments was I know there was a "standard" we had with the old WinQuake filtering and what we everybody settle on. * > If you have a geophone > this would normally be 4.5 Hz (WinSDR, .222 in WinQuake) or maybe 1 if you > gave a 1 Hz geophone or AS1 type of sensor. This number sets where the filter > starts to boost the lower frequencies to compensate for the drop off of > sensitivity below the period of the sensor. *This helps*......*you must be very careful to use hertz and frequency in the right programs. I have seen comments by Larry that he couldn't make up his mind ..... it is easy to make mistakes!!!* *Another problem to watch out for is the enable boxes ... they don't seem to stay checked*. *At first, I was confused why the filtering was inside WinSDR. Now, I get a more pleasing noise freer display. It makes sense!* > The high-pass filter sets how much > you want to extend the period of the sensor. It should be set to some number > below the period of the sensor. Depending on the sensor and electronics, mainly > the first op-amp, you might be able to extend the period by one decade. *What is this one decade?* *Does this mean if the pendulum frequency is ..04 that I can go as low as .008?* > > > Before adding the software filter to WinSDR and WinQuake I played around with > the Robert's circuit. My results regarding using this filter, both in hardware > and software, can be found here:http://www.seismicnet.com/epf/ > Hi Larry, > With regard to the 4.5 Hz comperiod compensation circuit, you have two series > high gain frequency compensating amplifiers, so you need at least a second order > high pass filter, or better, on the output as well as a 4th order LP filter to limit > HFsignals into the ADC. You have re-designed an amplifier board! > The feedback resistor R3 on the first LT1007 opamp needs a parallel capacitor to > reduce noise over ~10 Hz. > C10 and C33 at 22 muF look too large for a 4.5 Hz geophoneand the frequency > compensating amplifiers seem to have too high a DC gain (x50^2),which will likely > result inincreased 1/f noise. You need an achieved gain of x10^2 = 100 at 0.45 Hz. > I use x 20^2.Since the gain of the directchannel is 1 and the gain of the > amplified channel is also ~1 with a ~90 deg phaseat 4.5 Hz, won't thisgive a peak > in the output voltage?I am a bit puzzled as to the functional requirement of C9 ? > You might want to make the feedback resistor on U2C either variable or switch selected > to vairy the overall gain ? > We have used a slightly different circuit. > Regards, > Chris Chapman *At this point in the discussion of the circuit, might I ask why a feedback of some sort was never added to help on nearby quakes that overload the circuit? dickthomas01@............. * On 2/13/2012 5:49 AM, chrisatupw@....... wrote:

Larry Cochrane lcochrane@..............
Sent: Tue, 7 Feb 2012 6:12
Subject: Robert's circuit and new WinQuake / WinSDR releases

Hi Everyone,

In WinQuake the inverse filter can be found in the Time-Domain Filter

dialog box and in WinSDR the Channel Settings -> Integrate / Filter tab

dialog box.

A few days ago there were some emails on the list regarding what numbers

to use for the pendulum frequency and high-pass filter. The pendulum

frequency is the undamped period of your sensor.

I had been working with this program about 4 weeks now. I am not satisfied with the results. Bob's self-standing program seems better. What participated my comments was I know there was a "standard" we had with the old WinQuake filtering and what we everybody settle on.

If you have a geophone

this would normally be 4.5 Hz (WinSDR, .222 in WinQuake) or maybe 1 if you

gave a 1 Hz geophone or AS1 type of sensor. This number sets where the filter

starts to boost the lower frequencies to compensate for the drop off of

sensitivity below the period of the sensor.

This helps...... you must be very careful to use hertz and frequency in the right programs. I have seen comments by Larry that he couldn't make up his mind ..... it is easy to make mistakes!!! Another problem to watch out for is the enable boxes ... they don't seem to stay checked.

At first, I was confused why the filtering was inside WinSDR. Now, I get a more pleasing noise freer display. It makes sense!

 The high-pass filter sets how much

you want to extend the period of the sensor. It should be set to some number 
below the period of the sensor. Depending on the sensor and electronics, mainly 
the first op-amp, you might be able to extend the period by one decade.

What is this one decade? Does this mean if the pendulum frequency is .04 that I can go as low as .008?



Before adding the software filter to WinSDR and WinQuake I played around with 
the Robert's circuit. My results regarding using this filter, both in hardware

and software, can be found here: http://www.seismicnet.com/epf/

Hi Larry,

    With regard to the 4.5 Hz comperiod compensation circuit, you have two series

high gain frequency compensating amplifiers, so you need at least a second order

high pass filter, or better, on the output as well as a 4th order LP filter to limit

HF signals into the ADC. You have re-designed an amplifier board!

    The feedback resistor R3 on the first LT1007 opamp needs a parallel capacitor to

reduce noise over ~10 Hz.

    C10 and C33 at 22 muF look too large for a 4.5 Hz geophone and the frequency

compensating amplifiers seem to have too high a DC gain (x50^2), which will likely

result in increased 1/f noise. You need an achieved gain of x10^2 = 100 at 0.45 Hz.

I use x 20^2. Since the gain of the direct channel is 1 and the gain of the

amplified channel is also ~1 with a ~90 deg phase at 4.5 Hz, won't this give a peak

in the output voltage?  I am a bit puzzled as to the functional requirement of C9 ?

You might want to make the feedback resistor on U2C either variable or switch selected

to vairy the overall gain ?

    We have used a slightly different circuit.

    Regards,

    Chris Chapman

At this point in the discussion of the circuit, might I ask why a feedback of some sort was never added to help on nearby quakes that overload the circuit?

dickthomas01@.............

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