[ANSS-netops] L4 3 component mount

[David S. Croker]

Hey Steve, that looks awfully familiar.  We took our design from John 
Evans, who happens to be good buddies with John Rogers.  We do the 
same for electrical isolation too.  We do not weld our plates 
together.  I guess too much trouble.  We instead use 4 bolts in each 
channel to secure them to the bottom plate.  Of note, however, is we 
work hard to secure the seis cables as close to the cap as possible; 
for instance, we zip tie the vertical cable to one of the vertical 
threaded rods and have a cable clamp in the corner of the plate to 
secure all of the cords.  With even moderate shaking, the cords will 
start to shake and affect data.  The other big difference is we 
support the plate on heavy compression springs that fit around each 
of the mounting bolts.  Then, we compress the springs greatly so 
there is not too much play left, but enough to make the leveling 
process easy with a socket.  The design is such that you only need to 
adjust the west and south bolts, and once the two horizontals are 
level, by default the vertical will be level also.  This design has 
worked very well for us with no discernable differences in data seen 
in side-by-side testing with a direct buried L4 (that's with John 
Evans comparing seismograms too, and if you know John, he is as 
careful as they come).

Attached are a picture of the plate and our diagram.  The black box 
in the picture is where we terminate the seis cords and insert the 
S+T resistors, with one 3-pair individually shielded cable out to the 
digitizer.  Hope this helps.

Dave

At 03:15 PM 3/28/2012, Steve Estes wrote:
>Three component mount for L4C.
>Leveling of the mount is accomplished by using washers between the 
>mount and concrete.
>Electrical isolation, if desired, is accomplished using slotted PVC 
>pipe for the horizontals, and a PVC plate on the top and bottom of 
>the vertical.
>I was introduced to this design by John Rogers of Alaska Section of 
>USGS in about 1993.
>
>Regards,
>Steve
>
>
>
>
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