RE: [PSUBS-MAILIST] O2 & CO2 sensors

["Alec Smyth" <Asmyth@changepoint.com>]

Thanks for the research Cliff. I remember Carsten once said if an "electric madman" builds a sub, everything is electronic. If a "hydraulic madman" builds one, everything is hydraulic, and so on. I think I'm a machinist madman, so I'm tending towards mechanical solutions. I also think a simple mechanical solution has the least possible failure points... although an electronic madman would surely prove me wrong!

Anyway, my proposed mechanism is:

- A simple scrubber, with an option for lung power. I'm awaiting some parts and should be done in a few days... will post photos. I'm trying to make it as quiet as possible, because its going to be "always on".
- As scrubber consumes CO2, the cabin pressure drop will trigger a compensating O2 release, per Phil's white paper mechanical approach.

And the supporting instrumentation:

- An altimeter to monitor barometric pressure.
- A "handi" O2 monitor from www.maxtecinc.com

For monitoring CO2 I'd rely on the coloring of the absorbent, but also on something more rudimentary that us engineering types might have forgotten... the urge to breathe is not caused by lack of O2, it is caused by excessive CO2. So in a sense, this is the one gas we're designed to monitor without instruments. Hope that doesn't sound too primitive!

Backup systems are:

- If power fails, lung power the scrubber with the face mask.
- The scrubber has a respirator cartridge in addition to the absorbent. In conjunction with the mask, this should help if there is something noxious in the cabin air (e.g. smoke from some electrical fault).
- If there is O2 depletion (e.g. due to a fire) you can tap into the pressure compensation circuit or use the bailout SCUBA. Either case would lead to a gradual buildup of internal pressure, but hopefully you'd be on your way up or out by then.

Got to get back to the day job!

Alec


-----Original Message-----
From: Cliff Redus [mailto:dr_redus@devtex.net]
Sent: Thursday, September 12, 2002 10:56 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] O2 & CO2 sensors


Gary, for non ABS boats, I think this would work.  For ABS, rules require
monitoring CO2 ppm in order to stay below 5000 ppm.  Since I am trying to
stay within ABS framework, I will need sensor. Like everyone else that is
scrubbing CO2, I plan on using a clear cartridge holder and absorbent that
changes color on saturation as a backup indicator.  I cur with thoughts on
safety issues related to high O2 level and high cabin pressure.

Cliff


----- Original Message -----
From: "Gary R. Boucher" <protek@shreve.net>
To: <personal_submersibles@psubs.org>
Sent: Thursday, September 12, 2002 11:17 AM
Subject: Re: [PSUBS-MAILIST] O2 & CO2 sensors


> Hey Cliff,
>
>      Just had a primitive thought...   Do you really "need" a CO2
> sensor?  Many of the CO2 scrubbing products available use colored
> indicators which will allow you to see if the material has been
> exhausted.  Wouldn't a positive air flow indicator on the scrubber work as
> well?  If you know that cabin air is flowing through the material and the
> material is still active, couldn't you assume that the CO2 is being dealt
> with?
>      I do not use a scrubber on my sub, just SAR, surface and
> replenish.  However, my biggest fear would be from excess O2 or from
> overpressurization of the cabin.  Excess O2 levels can be a fire hazard
> (remember NASA's problem).  And, if for some reason, the inside of the sub
> had to be pressurized with a high O2 concentration, it could be toxic to
> the occupant.   The O2 sensor could warn you of this danger and a
barometer
> could warn against excess cabin pressure.  The flow meter and visual
> inspection of the scrubber material could warn against a potential lack of
> C02 removal.
>      I may just get me an O2 sensor for $77.  Course, I have no O2 to
> sense.  I love working with almost any type of sensor.  Makes me want to
> run design a circuit.  :-)
>
> Gary
>
>
>
>
> At 06:32 AM 9/12/2002, you wrote:
> >Alec, I to am working the O2 & CO2 sensor issue.  The www.amronintl.com
site
> >has a number of analyzers for O2, CO2 and combined units. This is a great
> >site.  You have to set up an account with them to get prices.  Having set
up
> >an account and checked out their prices, they are definitely set up for
> >commercial traffic.  Example, rack mounted O2 &CO2 unit (Sub Mk II - CO2,
> >O2, Depth) is over $7,000!
> >
> >Best I have found so far for Oxygen sensor is to use the Maxtec, formally
> >Ceramatec, CAG-250 sensor.
> >http://www.cisatlantic.com/trimix/Analyzer/analyzer.htm  shows how you
can
> >build a simple unit out of a CAG-250 sensor ($77) and some simple
electrical
> >components.  Since I am using a PLC and a touchscreen display, all I will
> >have to do convert the mV signal from the CAG-250, that is proportional
to
> >O2 partial pressure, into a 4-20 mA signal and waire to my PLC analog
input
> >module.
> >
> >So far I have not found a economical CO2 sensor. If anyone has a lead on
a
> >economical 4-20mA or mV output sensor for CO2, please post.
> >
> >Cliff
> >
> >
> >----- Original Message -----
> >From: "Alec Smyth" <Asmyth@changepoint.com>
> >To: <personal_submersibles@psubs.org>
> >Sent: Tuesday, September 10, 2002 2:09 PM
> >Subject: RE: [PSUBS-MAILIST] sofnolime
> >
> >
> > > Adam,
> > >
> > > I'm just building my scrubber. What are you using to monitor the O2
and
> >CO2? I'm curious if you've come across any economical analyzers you'd
> >recommend. Or are you bilding your own?
> > >
> > > thanks,
> > >
> > > Alec
>
>