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Re: [PSUBS-MAILIST] Another nutcase here.



deco comps reading wrong in air rather than water.
as a twenty year instrument tech i can't see that with a properly designed unit this should  happen. so lets look at the difference between the two occurances.
 
 
force applied to the transducer same in both instances.
force applied to the case same in both instances.
 
speed at which force was applied. distortion of the sensing plate unknown. most water test chambers are limited by design to a certian rate of chnge up and down. unknown design for the air chamber. have seen this happen with sensing line blow outs. posibility 
next thought
 
desity of the molicule
 
we know that helium leaks faster than air so lets assume that air leaks faster than water.
 
assumption case leak under air condition but minor
at the cost of deco comps they are not using absolute transducers they are using guage transducers that use the internal pressure as a reference for the difference with a corrrection factor for the compression of the case under pressure. And assume that they have a built auto calibrate feature for zero drift. if they case pressure exceeds the outside pressure than the unit goes into recalibrate mode and changes the baseline zero.
 
thats my idea,
ps shit poor design
rick.
 
note if you dive with deco comp ensure that the tranducers are absolute, that means that the reference is absolute vacume. this is cirtical in high altitude lake diving
 
rick miller
 
 
 
 
----- Original Message -----
Sent: Friday, October 28, 2005 5:34 PM
Subject: RE: [PSUBS-MAILIST] Another nutcase here.

Nobody ever was able to give a good reason, even a buddy who was on the design team for the one of the units.  This was noted in a number of deco computers?don?t know if it still occurs.

R/Jay

 


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Akins
Sent: Friday, October 28, 2005 8:40 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Another nutcase here.

 

Hi Jay.

 

That's good to know. Do you have any idea WHY it is inaccurate out of water?

 

Bill.

 

 

 

----- Original Message -----

Sent: Friday, October 28, 2005 7:46 PM

Subject: RE: [PSUBS-MAILIST] Another nutcase here.

 

When I have taken a dive computer on a chamber run or put it in a pressure pot resulted in inaccuracies when not submerged in water.

R/Jay

 


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Chuck Will
Sent: Friday, October 28, 2005 7:14 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Another nutcase here.

 

Even when computers are tested during repairs or calibration they are submerged in water in a small pressure tank. My old instructor trainer repairs dive equipment and he said exposure to increased pressure out of water can damage some computers. Don't know why, pressure is pressure if you ask me. But do you want to risk it on a $400 dive computer?

 

Chip

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Akins
Sent: Friday, October 28, 2005 4:15 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Another nutcase here.

Hi Chuck.

 

That sounds like a good idea too. But the easiest thing of all would be to use a non water activating dive computer that would just read

 

the air pressure as if it was water pressure.

 

Bill.

 

 

----- Original Message -----

From: Chuck Will

Sent: Friday, October 28, 2005 6:00 PM

Subject: RE: [PSUBS-MAILIST] Another nutcase here.

 

A little cleaner setup might be to use an acrylic box that is sealed but vented to the outside by a couple of tubes. One to bring in the outside water pressure and one to vent the air out of the box. That way no water is sloshed aroud in the bucket.

 

Chip

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Akins
Sent: Friday, October 28, 2005 3:08 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Another nutcase here.

Right on Paul.

 

You could put your dive computers into a small bucket of water inside the dry sub and then the pressure in the sub

 

pushing against the water in the bucket should register the interior pressure and make your dive computers depth gauge work.

 

Bill.

 

 

 

----- Original Message -----

From: Paul Kreemer

Sent: Friday, October 28, 2005 12:41 PM

Subject: Re: [PSUBS-MAILIST] Another nutcase here.

 

So treat an ambient dry sub like a dive with a big scooter.  I haven't thought much about ambient subs but this has prompted some rules I might set for myself:

* Be a certified diver.  The education on dive physiology and just general comfort underwater is crucial.

* Assume you'll be exiting in an emergency.  I'd think entanglement is one of the more likely accidents, particularly for those of us interested in shipwrecks. :-)  In cold water wear some kind of exposure suit - I can't see myself wearing my drysuit but at least a thicker wetsuit would help.  Weight belt, mask, survival gear, personal bail out bottle, maybe a 40cf pony?  That could be a lot of gear...  but still less than you'd wear on any normal cold water dive.  Store an ascent line/spool in an exterior compartment.  Think what you'll do on the surface, minus your diesel/electric boat.  :-(

* Have partial droppable ballast - as Rick describes.  And it sounds dangerous to have fully droppable ballast.  Right?

* Carry your dive computers and dive a plan.  I've done recreational diving with tables and with just one computer but would probably spring for a backup computer of a different model than my primary computer.  Yes, in a dry ambient you'd have to trick them into thinking they were submerged.


It seems like this being out of the water, even in a small sub may keep you warmer, and make it easier to manage gear, particularly breakdowns.  You can easily talk to your dive partner because he's sitting right there behind you.  I like it.  I have some of the slowest ears ever for diving and have the hope that equalizing in air may be easier for me than in water.  Also need to try the ProEar2000 mask or some kind of helmet, which would be much easier than building a sub to test this idea.  :-)

Great discussions on this list! 

Paul