Hello PSN;

I'm looking for an answer and maybe
someone can learn from my own experiences.

I just got done testing my system for damping
with a homemade rig as follows.

A 0.1 micro condenser is normally shorted
by a spdt push switch.

When the momentary switch is pressed
the current from the battery is allowed to
charge the capacitor through the dampened geophone.

This is a pulse several milliseconds long
but seems to test the device well
showing as a pulse on the chart.

current runs from a 1.5 v battery
through a 680K resistor
through the 380 ohm geophone
damping resistor pair.

I figure this puts a momentary
voltage of about 837 micro volts
to the geophone itself dieing
away quickly in several tens of milliseconds.

Seems to give a good damping picture
since the geophone is 1Hz.

I run the circuit through a DPDT switch
to clip leads which is wired to reverse polarity.

Here is what i found.

Given HS-10-1 1Hz about 450 Ohms
actually 438 in summer and less in winter.
depends on temp changes.

supposedly
CDR = 1179 ohms

When RT = 3842ohms up excursion about 5x amplitude downward
        = 3238                        7x
        = 2838                       10x (one of choice)
        = 2256                       over damped no excursions visible

RT = Rdamper + Rgeophone in parallel looping the current

from this i chose to use RT of 2838 ohms for my final value.
This means each excursion is 1/10 the previous or better
but still an excursion is visible.

I look at gain only at 1Hz and try to keep it about 54Dbv or X501
voltage gain AC which can translate to x10,000 or 80DBv DC between
input and output of everything between geophone (HS10-1) and the
16 Bit +/- 5V INPUT A/D converter. Overall Gain depends
upon filtering used. Even tho I try to keep the 1Hz the same.
This gives me a similar picture no matter what I choose to do.

Question here is:

Can someone here point me to a formula which converts
the 1:10 ratio to a damping number relating to 1.0
which is the calculated CDR of 1179 Ohms for this
HS10-1 geophone ?

Regards,
geoff

PS. I decided to use an instrumentation amplifier
even tho people don't seem to like these.

I allowed the test pulse to run through the entire
circuit which means I do not get the beautiful
perfect pulse, yet you can still see the damping
effects even with the filter distortions.
I have done this before in the past
to compare the two so I am relatively
confident of my results.

None of this has to do with your current chatter
relating to Damping. I have been wanting to do
this for a long time now and just got around
to building the amplifier I prefer.

I really hate to filter to get telesismic results
and think you need two separate circuits
to the same geophone, one for local/regional
and one for teleseismic both going to
separate A/D channels to be recorded
simultaneously.

relevant Comments welcome






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