In a message dated 08/05/2005, lcochrane@.............. writes:

Hi  Chris,

> Hi Larry,
>     Do you have any  figures, or preferably measurements, for the time 
> delay produced by  the filters on your amplifier boards, please?

I measured this a long  time ago. The delay is about 30 to 50 ms depending on 
the 
cut-off  frequency. I did the measurement by feeding in a square-wave and 
looking at  
the output with a o-scope.

>      Putting in the values for an 8th order 5 Hz Butterworth low pass 
>  filter suggest that the delay is likely to be ~160 milli sec below 2 Hz,  
> peaking to about 280 milli sec at 5 Hz.



Hi Larry,
 
    The calculated figure for your old board, which  used a 10 Hz 6 pole 
Butterworth filter, is a bit over 50  milli sec, which agrees with your old 
measurements.
 
    However, your current boards for a Lehman  use a 5 Hz 8 pole Butterworth 
filter. Reducing the  frequency to 5 Hz and adding a couple of stages pushes 
up the calculated  value to ~160 milli sec as above. 
 
    The calculated value for the 10 Hz 8 pole geophone  amplifier is ~75 
milli sec.
 
    Is there any chance of getting approximate  measurements for your current 
boards, please? 0.16 sec is an appreciable  correction. 
    Have you considered using Bessel filters, which  give a flat response 
with no transient impulse peaking? 
 
    Regards,
 
    Chris  Chapman 






 =20

In a message dated 08/05/2005, lcochrane@.............. writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000>Hi=20
  Chris,

> Hi Larry,
>     Do you have any=20
  figures, or preferably measurements, for the time 
> delay produced=20=
by=20
  the filters on your amplifier boards, please?

I measured this a lon=
g=20
  time ago. The delay is about 30 to 50 ms depending on the 
cut-off=20
  frequency. I did the measurement by feeding in a square-wave and looking a=
t=20
  
the output with a o-scope.
   
>    =
=20
  Putting in the values for an 8th order 5 Hz Butterworth low pass 
>=20
  filter suggest that the delay is likely to be ~160 milli sec below 2 Hz,=20
  
> peaking to about 280 milli sec at 5 Hz.


Hi Larry,
 
    The calculated figure for your old board, which=
=20
used a 10 Hz 6 pole Butterworth filter, is a bit ove=
r 50=20
milli sec, which agrees with your old measurements.
 
    However, your current boards for a Le=
hman=20
use a 5 Hz 8 pole Butterworth filter. Reducing the=20
frequency to 5 Hz and adding a couple of stages pushes up the calculate=
d=20
value to ~160 milli sec as above. 
 
    The calculated value for the 10 Hz 8 pole geoph=
one=20
amplifier is ~75 milli sec.
 
    Is there any chance of getting approximate=20
measurements for your current boards, please? 0.16 sec is an appreciabl=
e=20
correction. 
    Have you considered using Bessel filters, which=
=20
give a flat response with no transient impulse peaking? 
 
    Regards,
 
    Chris=20
Chapman