PSN-L Email List Message

Subject: Re: My seismometer vault solution
From: geodynamics@.......
Date: Sat, 28 Oct 2006 03:47:19 +0000


Chris,
The meltwater and rain percolation are just the things I'm concerned about. It is much more efficient to seal the small housing of the geophones than it is to seal a plastic bucket lid and the access hole. As long as Jon gets rid of the external splices (1-meter pigtail coming out from the geophone case) the geophone case should be sufficiently sealed to easily withstand the local climate and long-term burial. If he chooses to leave the splices then all bets are off because he's probably left a channel for moistrue migration into the geophone case.

Frankly, if it was mine, I wouldn't even bother with the plastic bucket. However, for Jon's installation the bucket does afford some additional protection, particularly when it comes time to dig it up again. I've had contless installations, both surface and subsurface for monitioring of both ground and structural vibrations. Many were in-place over a period of years using geophone cases very similar to the one Jon is using. The only problems we've had have occured when a subcontractor neglected to connect shield wires and, on the same job, just twisted wire splices instead of soldering them. We've never had a problem with moisture migration but we've always been careful to seal the cases with non-corrosive silicon sealant. One installation had triaxial sets about 20-feet below the groundwater level for over two years and they are still being used on other jobs, some 10-years later. Here in Michigan, we don't have the extremes that Iceland does but I'd suspect that we have more free
ze-thaw cycles -- and that's what typically causes the greatest problems.
Regards,
-Tim-
-------------- Original message from ChrisAtUpw@........ -------------- 

In a message dated 2006/10/27, geodynamics@....... writes:

Even slight jostling of the geophones can generate a pretty strong signal -- well in excess of 10-volts -- that can over-saturate or even damage some ADC boards.


Hi Tim,

       Jon is using one of Larry's amplifiers. It has 12 V rails.

       If Jon does as you suggest and the whole area floods with snow melt water, melts and re freezes a few times, won't it likely damage the geophones? The climate in Iceland is chilly in winter. I would enclose them in a sealed container under dry sand. It is not difficult to seal cable into plastic water pipe. You can easily buy tank fittings for plastic water pipe to seal to a container. 

       Can you check this message and see if there is a HTML attachment, please?

       Regards,






Chris,

The meltwater and rain percolation are just the things I'm concerned about. It is much more efficient to seal the small housing of the geophones than it is to seal a plastic bucket lid and the access hole. As long as Jon gets rid of the external splices (1-meter pigtail coming out from the geophone case) the geophone case should be sufficiently sealed to easily withstand the local climate and long-term burial. If he chooses to leave the splices then all bets are off because he's probably left a channel for moistrue migration into the geophone case.

 

Frankly, if it was mine, I wouldn't even bother with the plastic bucket. However, for Jon's installation the bucket does afford some additional protection, particularly when it comes time to dig it up again. I've had contless installations, both surface and subsurface for monitioring of both ground and structural vibrations. Many were in-place over a period of years using geophone cases very similar to the one Jon is using. The only problems we've had have occured when a subcontractor neglected to connect shield wires and, on the same job, just twisted wire splices instead of soldering them. We've never had a problem with moisture migration but we've always been careful to seal the cases with non-corrosive silicon sealant. One installation had triaxial sets about 20-feet below the groundwater level for over two years and they are still being used on other jobs, some 10-years later. Here in Michigan, we don't have the extremes that Iceland does but I 'd suspect that we have more freeze-thaw cycles -- and that's what typically causes the greatest problems.

Regards,

-Tim-
-------------- Original message from ChrisAtUpw@........ --------------

In a message dated 2006/10/27, geodynamics@....... writes:

Even slight jostling of the geophones can generate a pretty strong signal -- well in excess of 10-volts -- that can over-saturate or even damage some ADC boards.



Hi Tim,

       Jon is using one of Larry's amplifiers. It has 12 V rails.

       If Jon does as you suggest and the whole area floods with snow melt water, melts and re freezes a few times, won't it likely damage the geophones? The climate in Iceland is chilly in winter. I would enclose them in a sealed container under dry sand. It is not difficult to seal cable into plastic water pipe. You can easily buy tank fittings for plastic water pipe to seal to a container.

       Can you check this message and see if there is a HTML attachment, please?

       Regards,

       Chris Chapman

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