In a message dated 02/07/01, kd6iwd@......... writes:

> I made a seismic sensor out of a 1.5 inch piezo disk transducer. In my 
> application I was trying to detect footsteps. I was able to detect 
> footsteps at least 75
> feet away. Piezo transducers may be suitable for strong motion transducers 
> or even as general purpose geophones.

       With a 60 gm load on a 1/4" dia. central rod, the resonant disk 
frequency seems to be about 20 Hz. I found that my disks cracked at loads 
between 1.2 and 1.4 Kg dead weight on a central 1/4" dia rod stuck on with 
epoxy. With a LCT2201 amp, the piezo of 50 nF capacity seems to work OK into 
10 M Ohm (T=0.5 sec). A direct comparison with a L15B vertical geophone 
indicated that the piezo was giving about 5x the output. It should not be 
difficult to provide some oil damping for the piezo mass. There seems to be 
adequate performance from piezo devices to make them useful in principle for 
short period work. [Remembering that force = mass x acceleration, adding a 
mass maybe a hundred times the mass of the disk on it's own produces a huge 
increase in the output.]

       Regards,

       Chris Chapman
In a message dated 02/07/01, kd6iwd@......... writes:



I made
 a seismic sensor out of a 1.5 inch piezo disk transducer. In my 

application I was trying to detect footsteps. I was able to detect 

footsteps at least 75

feet away. Piezo transducers may be suitable for strong motion transducers 

or even as general purpose geophones.



       With a 60 gm load on a 1/4" dia. central rod, the resonant disk 

frequency seems to be about 20 Hz. I found that my disks cracked at loads 

between 1.2 and 1.4 Kg dead weight on a central 1/4" dia rod stuck on with 

epoxy. With a LCT2201 amp, the piezo of 50 nF capacity seems to work OK into 

10 M Ohm (T=0.5 sec). A direct comparison with a L15B vertical geophone 

indicated that the piezo was giving about 5x the output. It should not be 

difficult to provide some oil damping for the piezo mass. There seems to be 

adequate performance from piezo devices to make them useful in principle for 

short period work. [Remembering that force = mass x acceleration, adding a 

mass maybe a hundred times the mass of the disk on it's own produces a huge 

increase in the output.]



       Regards,



       Chris Chapman