## PSN-L Email List Message

Subject: Surface waves
From: "Randy" rpratt@.............
Date: Mon, 4 Jun 2007 12:46:25 -0500

```Bob,

Thanks for the reply on using the resistors to test RC filter of system. =
I didn't try it yet but it sounds very similar to the calibration =
method shown in the manual of seismological practice put to a different =
use.  I have tried that in the past and seen the decay curves you =
mention.  I would assume for the purpose of testing the filter response =
the boom would be locked or the coil disconnected completely to =
eliminate any mechanical response. =20

For gain computation do I just consider the input resistance as parallel =
to the 1K and figure drop across the pair as compared to the AD voltage?

Randy

----------------
If you want to assess the performance of your amplifier, I suggest a  =
step=20
function test. Make up a voltage divider consisting of, say, 1 megohm in =
=20
series with 1K. Connect the amplifier to the 1K. Apply a 1.5v battery =
across the =20
series combination of 1 meg and 1K while recording. You should see a =
sharp=20
jump  in ADC output, following by an exponential decay. The time =
constant of this=20
decay will give you the RC cutoff period. Removing the battery should =
yield =20
another transient of opposite sign. The high frequency gain of the =
amplifier=20
can  be calculated from the peak height of the transient, the voltage =
divider=20
ratio,  the amplifier input resistance, and the applied voltage.

Bob,

Thanks for the reply on using the =
resistors to test=20
RC filter of system.  I didn't try it yet but it sounds very =
similar to the=20
calibration method shown in the manual of seismological practice put to =
a=20
different use.  I have tried that in the past and seen the decay =
curves you=20
mention.  I would assume for the purpose of testing the filter =
response the=20
boom would be locked or the coil disconnected completely to eliminate =
any=20
mechanical response.

For gain computation do I just consider =
the input=20
resistance as parallel to the 1K and figure drop across the pair as =
compared to=20

Randy

----------------
If you=20
want to assess the performance of your amplifier, I suggest a  step =

function test. Make up a voltage divider consisting of, say, 1 =
megohm=20
in  series with 1K. Connect the amplifier to the 1K. Apply a =
1.5v=20
battery across the  series combination of 1 meg and 1K while =
recording.=20
You should see a sharp jump  in ADC output, following by an =
exponential=20
decay. The time constant of this  decay will give you the RC =
cutoff=20
period. Removing the battery should yield  another transient of =

opposite sign. The high frequency gain of the amplifier can  be =

calculated from the peak height of the transient, the voltage divider=20
ratio,  the amplifier input resistance, and the applied=20
voltage.
```