PSN-L Email List Message

Subject: Re: Trigger
From: "Geoffrey" gmvoeth@...........
Date: Wed, 18 Jul 2007 18:36:44 -0700

By trigger I assume you mean an ALARM
it might be best as a TRIGGER/ALARM combination.

That is what i do here at GVA.

I recommend a frequency sensitive trigger that will respond only at or below one or two hertz.

Look at only the positive half cycle and look at
the contiguous ( yes contiguous) string of samples on the plus side
that represents the freq of interest.

Set a thresh hold above the baseline to measure the contiguous samples.

Like a venus fly trap look for three triggers in a certain length of time.

If you do not achive the proper alarm conditions reset everything to zero
and start looking again.

Make your recorder modulo 12 or 15 minutes and you should never
miss any worthwhile Earthquakes.

Make it modulo in RAM then when the recording is triggered
complete the data set. Straighten out the modulo stuff just before
you save the EQ file.

When the alarm is triggered jump to the end of
modulo secton to continue the recording in RAM
to its ultimate limit before saving.

You can do this all automatically with home written code.

It would be nice if it were standardized tho.

Use an UPS system to guard against power failures.
One that will allow an hour or more of power loss.

Make the numbers adjustable during operation
so you do not have to recompile the program
each time you want to make any changes.


----- Original Message ----- 
Sent: Wednesday, July 18, 2007 07:14
Subject: Trigger

Hi Folks,  I would like to have or create a trigger program to work with AmaSeis.  I know very little about a trigger program, but I 
guess it runs in the background and when an earthquake occurs it set off an alarm, of some kind.

I see some helicorders which show earthquakes in red and background noise in black, and there maybe programs which trigger a .wav 
file or something.

If someone has info and experience on this subject, or even a program please contact me.  The only thing I would like, is so that it 
works with AmaSeis as I use it as my helcorder.

Thanks, Ted


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