PSN-L Email List Message

Subject: Re: Simple broadband Seismometer
From: Ian Smith ian@...........
Date: Fri, 02 Sep 2005 08:00:12 +0100


excuse my dumbness!  I'm treating this mailing list the same way I treat 
coffee time at work with my fellow engineers, as a forum for throwing up 
dumb ideas with the hope that about 1 in 10 fly (a reasonable rate).


The long length is to amplify the effect of very small tilts to the 
point that the effect is measurable.  10 m is a figure chosen for easy 

If the signals from the 2 piezo transducers are differenced then drifts 
and tempco's should cancel out.

The discussions here on how to measure the effect the easy way seemed to 
be quite complicated.

Longer periods are good!  During the recent hurricane, my medium period 
sensor was useless whilst the professional long period devices rolled on.

Having said all that, there's at least a 90% chance that my idea is 
indeed dumb!

Pass the coffee...


ChrisAtUpw@....... wrote:
> In a message dated 01/09/2005, ian@........... writes:
>     Hi,
>     one assumption I made was that the mean signal, generated by the
>     mean mass is subtracted and you are then only measuring the
>     changes.  If some piezo sensor can withstand a load generated by 44
>     Kg (2 supports), then 2 of them might give the required signal.  By
>     electrically differencing the signals from the 2 piezo sensors, the
>     remainder is the changing mass + noise.  Just a thought...
> Hi Ian,
>     I don't really see why you need such a large pipe, when something 
> nearer 1" would do fine. If you put on larger diameter end pots, you 
> increase the period.
>     Trying to match up two sensors allowing for temperature coefficients 
> and drifts just doesn't work to better than about 0.1%.
>     When it is dead easy to measure water levels to microns, why bother 
> with weight sensors? The inexpensive piezo sensors drift in output 
> voltage with temperature.
>     There re plenty of problems in making precision measurements. 'Doing 
> things the hard way' is just plain dumb.
>     Regards,
>     Chris Chapman


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