[ANSS-netops] l4c

[Greg Steiner]

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.
Greg Steiner

On 3/5/2012 6:00 AM, anss-netops-request at geohazards.usgs.gov wrote:
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>     1. L-4C sensors (Steve Estes)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sun, 4 Mar 2012 10:00:45 -0900
> From: Steve Estes<estes at gi.alaska.edu>
> To: anss-netops at geohazards.usgs.gov
> Cc: Guy Tytgat<guy at passcal.nmt.edu>
> Subject: [ANSS-netops] L-4C sensors
> Message-ID:<5F6AAFDB-1974-4021-BCAF-62796618FA90 at gi.alaska.edu>
> 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
>
>
>> Date: Fri, 02 Mar 2012 13:34:11 -0800
>> From: "David S. Croker"<croker at usgs.gov>
>> To: anss-netops at geohazards.usgs.gov
>> Subject: [ANSS-netops] L-4C users beware
>> Message-ID:<OFD86DC885.EBFA1C35-ON882579B5.00767C4A at usgs.gov>
>> 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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