In a message dated 09/08/2005, gmvoeth@........... writes:

The  Piezo Idea is very interesting

Have you ever heard of a strain guage  approach where you just hang a 10# or 
so weight from a strainguage and measure  the tiny weight changes due to 
ground acceleration ??
Hi there,
 
    The strain gauge a) will not be anything like  sensitive enough b) it is 
quite fragile and won't take overloads c) as primarily  a resistive device, it 
has a fairly high power dissipation d) they are not  exactly cheap.

It  sounds a lot like the piezo idea but a strain guage would be resistive in 
 nature I believe.
    The maximum output is less that 1% of the  input voltage.

At the  moment I am using the top 9 bits of a 12 bit A/D converter looking at 
a +/-  2.048 voltage swing through amplifier filter with a gain of about 90DB 
will  that same setup work with the piezoelement ?
    I don't know your instrument setup and your  description does not make it 
clear. I would not expect you to need 90 dB  gain.

Do I  need a special preamp for the piezo element ?
    Does your amplifier have a low noise CMOS input  opamp with a controlled 
DC impedance of 100 M Ohms? 
 
    Are you just starting seismology and electronics? 
 
    Regards,
 
    Chris Chapman








In a message dated 09/08/2005, gmvoeth@........... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>The=20
  Piezo Idea is very interesting

Have you ever heard of a strain guag=
e=20
  approach where you just hang a 10# or so weight from a strainguage and mea=
sure=20
  the tiny weight changes due to ground acceleration ??
Hi there,
 
    The strain gauge a) will not be anything like=20
sensitive enough b) it is quite fragile and won't take overloads c) as prima=
rily=20
a resistive device, it has a fairly high power dissipation d) they are=20=
not=20
exactly cheap.
<=
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  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>It=20
  sounds a lot like the piezo idea but a strain guage would be resistive in=20
  nature I believe.
    The maximum output is less that 1% of the=20
input voltage.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>At the=20
  moment I am using the top 9 bits of a 12 bit A/D converter looking at a +/=
-=20
  2.048 voltage swing through amplifier filter with a gain of about 90DB wil=
l=20
  that same setup work with the piezoelement ?
    I don't know your instrument setup and your=20
description does not make it clear. I would not expect you to need 90 dB=20
gain.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Do I=20
  need a special preamp for the piezo element ?
    Does your amplifier have a low noise CMOS input=
=20
opamp with a controlled DC impedance of 100 M Ohms? 
 
    Are you just starting seismology and electronic=
s?=20

 
    Regards,
 
    Chris Chapman