In a message dated 09/05/2010, tchannel@............ writes:

Could someone give me the site, and or  information on how to extend the 
short period sensors?
Thanks, Ted



Hi Ted,
 
    You really need a 16 bit ADC to get  enough resolution and preferably 
also a 1/f^2 law amplifier. The AS-1  mechanics has a period of ~1.5 seconds. 
To extend this to 20 seconds requires an  ADDITIONAL amplification at 20 
seconds of (20/1.5)^2 = 178 = ~8 bits. 
    This is not difficult to do with a 2 amplifier  sections, each section 
giving x13.34 gain at 20 seconds with a 2 stage high pass  filter in 
between, set at say ~30 seconds. The Roberts compensator is described  at 
_http://www.jclahr.com/science/psn/roberts/index.html_ 
(http://www.jclahr.com/science/psn/roberts/index.html)  You  need two of these circuits in series linked 
by the two pole high pass filter. If  you don't put in the HP filter, you see 
lots of large amplitude long period  noise. 
Go to _www.ti.com_ (http://www.ti.com)  and check for a  download of 
Filterpro _http://focus.ti.com/lit/an/slyt113/slyt113.pdf_ 
(http://focus.ti.com/lit/an/slyt113/slyt113.pdf)  It  looks like they now ask you to register.
 
    Regards,
 
    Chris Chapman






In a message dated 09/05/2010, tchannel@............ writes:

  
Could someone give me the site, and or=
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  information on how to extend the short period sensors?
  
Thanks, Ted

Hi Ted,
 
    You really need a 16 bit ADC to get=20
enough resolution and preferably also a 1/f^2 law amplifier. The AS-1=
=20
mechanics has a period of ~1.5 seconds. To extend this to 20 seconds requi=
res an=20
ADDITIONAL amplification at 20 seconds of (20/1.5)^2 =3D 178 =3D=
 ~8 bits.=20

    This is not difficult to do with a 2 amp=
lifier=20
sections, each section giving x13.34 gain at 20 seconds with a 2 stage hig=
h pass=20
filter in between, set at say ~30 seconds. The Roberts compensator is desc=
ribed=20
at http:=
//www.jclahr.com/science/psn/roberts/index.html You=20
need two of these circuits in series linked by the two pole high pass filt=
er. If=20
you don't put in the HP filter, you see lots of large amplitude long=
 period=20
noise. 
Go to www.ti.com and check for=
 a=20
download of Filterpro http://focus.ti.com/lit/an/slyt113/slyt113.pdf It=20
looks like they now ask you to register.
 
    Regards,
 
    Chris Chapman