[PSUBS-MAILIST] Backup CO2 Meter

Thu Jul 16 17:08:19 EDT 2020

OK, I should clarify that... I don't use an altimeter for measuring CO2
directly. Here's what I do:

The scrubber runs continuously. As it does so, CO2 is taken out of the
cabin atmosphere. This reduces the cabin pressure. The O2 bleed also runs
continuously. This adds to cabin pressure.
What an altimeter will show is whether the cabin pressure is increasing or
decreasing. If it is increasing, that means your O2 bleed exceeds the CO2
absorption, so you should reduce the O2 bleed rate. Conversely, if the
pressure is falling you need to increase the O2 bleed. BTW it is unrelated
to life support, but an altimeter also helps insure against blowing out
your viewports due to internal pressure.

 Even for a small sub like a K250, this is a slow-mo process that does not
require you to adjust the bleed rate more than about once every 20 or 30
minutes. If it were something that required constant adjustment, I'd
automate it with electronics or with a mechanical system such as Phil
Nyutten's bellows-add mechanism. But for me, the simplicity of a manual
bleed is more valuable than automating a process that is not taxing.

What could throw off the method is an accidental slow leak of HP air or O2
into the cabin. Let's say you had an accidental release of air. It would
lead you to add too little O2, so O2 concentration would fall. Or if the
leak were of O2, that would lead O2 concentrations to be too high. For that
reason, you need to have an O2 monitor with high and low alarms. Low O2 is
a serious problem because you can pass out unexpectedly. High O2 is also
bad, because the cabin atmosphere would become combustible.

Another problem would be if the scrubber failed. That would lead to
excessive CO2. But this is way less worrying than high or low O2, because
the human body has a built-in CO2 sensor. When air feels stale, it is not
low O2 we are detecting, it is high CO2. This means a high CO2 condition
does not creep up and surprise you. Kittredge originally didn't have any
life support at all, because the Navy subs he served on didn't have it
either. I dove Snoopy many times before adding life support. The air only
became noticeably stale after over an hour, and at that time I would use
Kittredge's method of surfacing and opening the hatch.

Best,
Alec

On Thu, Jul 16, 2020 at 4:39 PM k6fee via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> How do you use an altimeter to determine CO2 levels???
>
> Keith T.
>
> -------- Original message --------
> From: hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org>
> Date: 7/16/20 10:55 AM (GMT-08:00)
> To: James Frankland via Personal_Submersibles <
> personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] Backup CO2 Meter
>
> James, your altimeter-if you have one, is your back up.  I know Alec only
> uses an altimeter for CO2 reading.  David Columbo and I am several dives
> with just the Altimeter and O2 readings in Montana last summer.
> Hank
>
> On Thursday, July 16, 2020, 9:58:33 AM MDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Yes, seen that one also thanks.  Think it might be ok for a backup.  Says
> it doesnt meet various regulations and reviews on Amazon are mixed.  But
> its cheap!
>
> So far that one is in the lead.  I'll wait until tomorrow just in
> case someone comes up with a better suggestion overnight.  You never know.
>
>
> On Thu, 16 Jul 2020 at 16:15, Jon Wallace via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Check out this one.  Not sure what the operating voltage is, but I'm
> guessing the transformer brings it to 9v or so.
>
> TIM10 Desktop CO2, Temp. & Humidity Monitor
> <https://www.co2meter.com/products/tim10-desktop-co2-temp-humidity-monitor?utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=Cj0KCQjw9b_4BRCMARIsADMUIyqYfY2gSWbBMp2xj9ASOmeGGkpsnm67YgCIDq469755nEY53CjlEzkaAg_7EALw_wcB>
>
> $129.00
> TIM10 Desktop CO2, Temp. & Humidity Monitor
>
> The TiM10 continuously shows carbon dioxide, temperature and relative
> humidity levels so you can monitor the qua...
>
> <https://www.co2meter.com/products/tim10-desktop-co2-temp-humidity-monitor?utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=Cj0KCQjw9b_4BRCMARIsADMUIyqYfY2gSWbBMp2xj9ASOmeGGkpsnm67YgCIDq469755nEY53CjlEzkaAg_7EALw_wcB>
>
>
>
>
>
>
>
> On Thursday, July 16, 2020, 09:36:15 AM EDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> That one looks good Hank, seen that one before.  Just a bit pricey.  I ws
> kind of hoping to keep the cost under £100 as its only a backup.
>
>
>
>
>
> On Thu, 16 Jul 2020 at 12:04, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>                                             HT-2000 Digital CO2 Meter
> Detector 9999ppm Temperature Relative Humidity Monitor Data Logger
>
> <https://www.amazon.ca/D%C3%A9tecteur-Num%C3%A9rique-Temp%C3%A9rature-dHumidit%C3%A9-Enregistreur/dp/B07D3QXC21/ref=sr_1_12?dchild=1&keywords=co2+meter&qid=1594897320&sr=8-12>
> On Thursday, July 16, 2020, 1:48:45 AM MDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Hi Jon.
> Looking for a complete unit.
>
> On Wednesday, 15 July 2020, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> These guys are good
>
> https://www.co2meter.com/ collections/products
> <https://www.co2meter.com/collections/products>
>
> Brian
>
>
>
>
>
> --- personal_submersibles at psubs. org <personal_submersibles at psubs.org>
> wrote:
>
> From: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.
> org <personal_submersibles at psubs.org>>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org <personal_submersibles at psubs.org>>
> Subject: Re: [PSUBS-MAILIST] Backup CO2 Meter
> Date: Wed, 15 Jul 2020 18:34:52 +0000 (UTC)
>
> Are you looking for a sensor that you can interface to a microprocessor,
> or an all-in-one monitor that contains both the sensor and display?
>
> On Wednesday, July 15, 2020, 12:20:09 PM EDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs. org
> <personal_submersibles at psubs.org>> wrote:
>
>
> Hi All,
>
> Im going to get another CO2 monitor, as a backup.  I have decent, properly
> calibrated one, so i dont want to break the bank with this one.
>
> Anyone got any ideas for a reasonably priced backup? It needs to go up to
> at least 1% really.
>
> What are other people using?
> Thanks
> james
>
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