[ANSS-netops] reftek unity or x32?

[Philip Crotwell]

Hi Mitch,

We have a couple of stations with reftek 130s at 32x gain, but the
reason has nothing to do with trying to make the data "better". Rather
there is a bug in the reftek to earthworm module such that if you are
using compression (CO or C2 in the reftek) and the data is relatively
quiet (low count range), then the reftek can compress more the data
for transmission in each packet (>1008 samples) than earthworm allows
in its internal tracebuf (1008 samples == 4032 bytes) packets. Hence
earthworm tosses those packets and you have lots of little gaps.

You might not have this problem with an S13, but if you see messages
from reftek2ew about packet too large, then you might need to ether
back off on the compression, or bump up the gain so that it doesn't
compress as well. The other odd thing about this is that the error
message from reftek2ew tells you that the packet is too big, but
doesn't tell you which station it came from, so finding the guilty
party can be a big challenging. The message (actually reported by the
wave server) looks like:

20080702_UTC_01:50:12 wave_serverV: tport msg[6288] i255 m50 t19 too
big. Max is 4096

It would be nice if reftek2ew would recognize that the packet was too
big and split it into two, but my understanding is that ain't the way
it works now.

Good luck,
Philip

On Mon, Mar 21, 2011 at 11:02 AM, Mark E. Meremonte <meremonte at usgs.gov> wrote:
> Hi Mitch,
>
> I discovered that the S13 is about 30 times more sensitive than the L22.
> Thus I would use unity.
>
> Mark
>
> At 01:10 3/18/2011, Mark E. Meremonte wrote:
>
> In Haiti we used L22s with 32x and .8 damping with good success.  However,
> the S13s are more sensitive.  Croker makes good point that local s/n
> conditions may help the decision.
>
> Mark
>
>
> At 16:49 3/17/2011, mwithers at memphis.edu wrote:
>
> We're upgrading some of our analog 3-c S-13 sites to digital telemetry
> and Reftek RT130 DAS's.  We're trying to decide whether to run at
> unity or x32 gain.  Being lazy and indecisive, my immediate question
> is what do other people do?
>
> Mitch
>
> Center for Earthquake Research and Information (CERI)
> University of Memphis                Ph: 901-678-4940
> Memphis, TN 38152                   Fax: 901-678-4734
>
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> Mark E. Meremonte        Geophysicist    USGS/ANSS/NEIC
>
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> *********************************************************
> Mark E. Meremonte        Geophysicist    USGS/ANSS/NEIC
>
> U.S. Geological Survey        Work: 303-273-8670   Cell: 303-478-5766
> MS 966, Box 25046          Email: meremonte at usgs.gov
> Denver, CO  80225             Web: http://geohazards.cr.usgs.gov
>
> Ship:  U.S. Geological Survey, 1711 Illinois St., Golden, CO 80401
> **********************************************************
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