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
the AD voltage?
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.
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