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Greg, Steve,<br><br>
Interesting stories that I can't say I ever knew. After talking to
Scott Bowen at Sercel, he definitely verified that. He's been with
Mark Products/Sercel for 30 years and he remembers that the reversal was
already in place when he started. So, I'm guessing that IRIS and
other university cooperators are using L-4C's that are reverse polarity
from USGS networks? Interesting.<br><br>
The geophone cables/caps that we ordered, however, are all supposed to
come out of the factory wired one way. He acknowledged they made a
mistake in manufacturing and missed it during QC. Of course they
are replacing the cables for us, but not after a bit of extra work.
Just wanted others to be conscience of the issue.<br><br>
Dave<br><br>
At 06:10 AM 3/5/2012, Greg Steiner wrote:<br>
<blockquote type=cite class=cite cite="">FYI, the polarity difference is
not restricted to just the L-4. All sensors (nominally called geophones)
manufactured by exploration type sources are backwards versus
seismological standards. This is because the exploration standard is
based on the movement of the inertial mass not the case. for them
movement of the inertial mass up or in the desired direction produces a
positive output. I'm a bit surprised that the USGS was able to get them
to invert their connections in sensors made for them. this certainly
muddies the water. <br>
<font color="#006600">Greg Steiner<br><br>
On 3/5/2012 6:00 AM,
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anss-netops-request@geohazards.usgs.gov</a> wrote: <br>
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Today's Topics:
1. L-4C sensors (Steve Estes)
----------------------------------------------------------------------
Message: 1
Date: Sun, 4 Mar 2012 10:00:45 -0900
From: Steve Estes
<a href="mailto:estes@gi.alaska.edu"><estes@gi.alaska.edu></a>
To:
<a href="mailto:anss-netops@geohazards.usgs.gov">
anss-netops@geohazards.usgs.gov</a>
Cc: Guy Tytgat
<a href="mailto:guy@passcal.nmt.edu"><guy@passcal.nmt.edu></a>
Subject: [ANSS-netops] L-4C sensors
Message-ID:
<a href="mailto:5F6AAFDB-1974-4021-BCAF-62796618FA90@gi.alaska.edu">
<5F6AAFDB-1974-4021-BCAF-62796618FA90@gi.alaska.edu></a>
Content-Type: text/plain; charset="us-ascii"
We ordered some L4C's awhile back and discovered the same thing.
The polarity was reversed. Well, at least it was different.
After discussing the issue with the manufacture (I don't remember if it
was Mark Products or Sercel),
we were told that they make all USGS orders oneway, and everyone else's
the other way.
As I recall the story, the USGS evaluated the original prototype and
found the polarity reversed.
Mark Products, wanting to please their customer, manufactured all
subsequent USGS L4C's to the USGS spec.
All others were made with the original polarity.
Regards,
Steve Estes
</pre><font face="Courier New, Courier" color="#006600"></font>
<blockquote type=cite class=cite cite=""><br>
<pre>Date: Fri, 02 Mar 2012 13:34:11 -0800
From: "David S. Croker"
<a href="mailto:croker@usgs.gov"><croker@usgs.gov></a>
To:
<a href="mailto:anss-netops@geohazards.usgs.gov">
anss-netops@geohazards.usgs.gov</a>
Subject: [ANSS-netops] L-4C users beware
Message-ID:
<a href="mailto:OFD86DC885.EBFA1C35-ON882579B5.00767C4A@usgs.gov">
<OFD86DC885.EBFA1C35-ON882579B5.00767C4A@usgs.gov></a>
Content-Type: text/plain; charset="us-ascii"; format=flowed
If you don't use Sercel L-4C sensors you can delete this.
We recently found out the hard way that a batch of "new"
seismometer
caps were wired with reverse polarity from the factory. This is
something we have never really checked before. The red lead
(positive, high) should go to the bottom contacts (closest to the
tip). We haven't bought many replacements over the years but we did
buy a batch of a dozen last year. It appears they were all wired in
reverse. Fortunately we caught the problem before we had too many
deployed and they were all a day trip away.
If you have purchased new caps from Sercel in the past year I
recommend you check the polarity.
Dave
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