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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>
Greg Steiner<br>
<br>
On 3/5/2012 6:00 AM, <a class="moz-txt-link-abbreviated" href="mailto:anss-netops-request@geohazards.usgs.gov">anss-netops-request@geohazards.usgs.gov</a> wrote:
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cite="mid:mailman.3.1330948801.17297.anss-netops@geohazards.usgs.gov"
type="cite">
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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 class="moz-txt-link-rfc2396E" href="mailto:estes@gi.alaska.edu"><estes@gi.alaska.edu></a>
To: <a class="moz-txt-link-abbreviated" href="mailto:anss-netops@geohazards.usgs.gov">anss-netops@geohazards.usgs.gov</a>
Cc: Guy Tytgat <a class="moz-txt-link-rfc2396E" href="mailto:guy@passcal.nmt.edu"><guy@passcal.nmt.edu></a>
Subject: [ANSS-netops] L-4C sensors
Message-ID: <a class="moz-txt-link-rfc2396E" href="mailto:5F6AAFDB-1974-4021-BCAF-62796618FA90@gi.alaska.edu"><5F6AAFDB-1974-4021-BCAF-62796618FA90@gi.alaska.edu></a>
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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>
<blockquote type="cite">
<pre wrap="">Date: Fri, 02 Mar 2012 13:34:11 -0800
From: "David S. Croker" <a class="moz-txt-link-rfc2396E" href="mailto:croker@usgs.gov"><croker@usgs.gov></a>
To: <a class="moz-txt-link-abbreviated" href="mailto:anss-netops@geohazards.usgs.gov">anss-netops@geohazards.usgs.gov</a>
Subject: [ANSS-netops] L-4C users beware
Message-ID: <a class="moz-txt-link-rfc2396E" 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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