----- Original Message -----
Sent: Sunday, August 28, 2005 4:41
PM
Subject: Re: Re: Re: [PSUBS-MAILIST] O2
sensors
Hi,
I honestly think that it would be better to get rid of the pressure
data in your oxygen anyzing process.
if the gas analyzed is a one atmosphere gas of course the partial
pressure displayed by the meter will be also the oxygen percentage.
for example air contains 0.21 of oxygen (21 %) so at one atm ppo2
is 0.21x1=0.21
but the percentage of o2 let's call it the fraction of oxygen is not a
good data to lett you know you if you are breathing a good o2 mix or a
bad one.
in any pressure condition if your partial pressure is between 0.16 bars
and 1.6 bars you are breathing a good mix.
a simple o2 sensor a voltmeter and a potentiometer is enough to display
the partial pressure.
if you really need to know the %tage of o2 you will have to use a
microcontroller that will read both the partial pressure from the
O2 sensor using an a/d converter and the pressure via a pressure sensor
which is really difficult to master unless you are a good digital
electronician, then the microcontroller will divide the partial pressure by
the pressure in ATM and you'll get de fraction or the percentage of o2
displayed via an ascii lcd digital display
but keep in mind that the percentage of o2 is only a usefull data at
one atmosphere but as soon as the pressure is going to change the o2
percentage is not a relyable data.
if you are breathing 21% of o2 in a 600 mb atmosphere you will loose
collapse.
21x.6=12,6 bars hypoxic lethal
o the other hand if you are breathing 15% o2 in a 1500 mb atmos
15x1.5=22,5 bars normoxic safe
in both cases o2 fraction will be a bad friend for you
in your cabins pressure can go down when you breathe a part of the
o2 without replacing it and getting rid of o2 via soda sorb
scrubbers or it could increase in case of a leak of air or o2
supply in the cabin.
in bith case the only inportant data is the O2 partial pressure and
NOT the fraction
so what is interresting for you is the partial pressure
in mix gas diving and in diving chambers we know :
- a mix at less then 0.16 bars of o2 is hypoxic blellow it get
dangerous , we trimix divers all breathe 0.16 trimixes at surface it is
ok but not bellow.
- for long periods in habitats of chambers the max ppo2 is arround 0.4
bars of o2 after there is an iritation of the lung (no serious but not
pleasant)
- for short periods max partial pressure is 1.6 bars O2 short means
arroud one hour , for 2 hours 1.5 is better and for 3 hours divers stay in
general under 1,4.
for all thoses reasons i think that it would be mutch easier just
to buit a simple analogic ppo2 analyser, that would be cheap ,
relyable well known .
hope it will help
regards
jean mi
----Message d'origine----
Date: Sun, 28 Aug 2005 15:56:46
-0400
De: Marie-Andrée et Pierre
Sujet:
Re: Re: [PSUBS-MAILIST] O2 sensors
A:
personal_submersibles@psubs.org
Thank you Al and Jean-Michel for the
reply,
Both of you have home-made rebreather. I
think that the application I want to do is very similar because both are
ambient pressure.
So do you guys have a pressure sensor in
combination with the O2 sensor? So the "computer" can divide the partial
pressure of O2 by the ambient pressure and give a reading equivalent to
1atm? (0.21 being normal even if taken at 2ATM)
I can't see another way to do that. Otherwise
the reading doesn't make sense if you don't take the ambient ATM into
account.
Am I right in assuming this? And if so, what
type of pressure sensors do you guys use?
Thanks again for the replies! It really help me
out!
Pierre Poulin
----- Original Message -----
Sent: Sunday, August 28, 2005 2:54
PM
Subject: Re: Re: [PSUBS-MAILIST] O2
sensors
Yes as a home made close circuit rebreather diver i can say that a
ppo2 meter is really simple to built.
basicly a simple 10 dollars lcd voltmeter and a pot are enough for
the electronics
but with no alarm
a system with an audible alarm can also be built cheaply .
what ojne have to know is that an o2 sensor is a very
fragile electrochemical device that can drift from a second to the
other with no warning
so any vital ppo2 system need to be doubled or trippled to be
abble for the operator to compare the readings
with 2 sensors one can know if the system works (if the reading are
close)
with 3 sensors one can know witch sensor is bad in case one starts to
drift .
a sensor life is usualy 12 to 24 monthes
as for the humidity problem don't care the r 22's have hydrophobic
membranes and works well in hyper humid condensing conditions like
rebreathers so i a bigger space like a sub cabin it will definitly be
better.
I can help if necessarry.
regards
jean mi
----Message d'origine----
>Date: Sun, 28 Aug
2005 10:13:11 -0400
>De: Al Secor
>A: personal_submersibles@psubs.org
>Sujet: Re: [PSUBS-MAILIST] O2 sensors
>
>Pierre,
>
>O2 sensors measure partial pressure of O2, so if your sub
cabin is at 2 atm, the
>sensor will read ..42 in air (assuming it's
been calibrated to .21 at 1 atm).
>Be aware that condensation on
the face of the sensor can lead to erroneous
>readings so you want
to try to avoid condensation directly on the face even
>though some
are manufactured with hydrophobic membranes.
>
>A good place
to get sensors is from Patrick at oxycheq.com. His prices are very
>reasonable and he provides good service. (I have no relation to
Patrick, just
>a satisfied customer). I use Teledyne R-22D sensors
in my homebuilt
>rebreather. A very simple O2 meter can be built
from a recalibrated DVM
> module. There are several sources on the
web that describe how to do it and I
>think Patrick's webpage also
describes it.
>
>Hope this helps.
>
>Al
>
>Al Secor ARS: WA3PWX Scuba Instructor SSI PDIC TDI
>http://www.geocities.com/SubDiverI
>
>
>
>Quoting Marie-Andrée et Pierre :
>
>> Hi guys,
>>
>> After seing Jon's
presentation at the convention I decided to go with a
>>
scrubber and a O2 injection device.
>>
>> My question
is: Will an oxygen sensor work for a dry-ambient sub? How does
>> the sensor work? I know it give a different voltage outpout
depending on the
>>
>> amount of oxygen in the air.
but what happened when put under pressure? Will
>>
>>
it track PPM of oxygen in the air or the % of oxygen in the air? Will it
>> detect 21% at 1atm, 42% at 2atm, 176% at 5atm, etc...
>>
>> Does anybody here have experience with a
scrubber/O2 system in an ambient
>> sub?
>>
>> The reason I decided to go scrubber/O2 is that I have about
35-40 minutes
>> inside my sub before I feel the effect of too
much CO2 in the cabine. If I
>> refresh the air inside the
cabine by injecting fresh air from my tanks, it
>> is not very
effective and takes alot of air.
>>
>> Thank you all!
>>
>> Pierre "O2" Poulin
>>
>>
>>
>>
>>
>>
************************************************************************
>>
************************************************************************
>>
************************************************************************
>> The personal submersibles mailing list complies with the US
Federal
>> CAN-SPAM Act of 2003. Your email address appears in
our database
>> because either you, or someone you know,
requested you receive messages
>> from our organization.
>>
>> If you want to be removed from this mailing list
simply click on the
>> link below or send a blank email message
to:
>> removeme-personal_submersibles@psubs.org
>>
>> Removal of your email address from this mailing list occurs
by an
>> automated process and should be complete within five
minutes of
>> our server receiving your request.
>>
>> PSUBS.ORG
>> PO Box 311
>> Weare, NH
03281
>> 603-529-1100
>>
************************************************************************
>>
************************************************************************
>>
************************************************************************
>>
>>
>
>
>
>
>
>
************************************************************************
>************************************************************************
>************************************************************************
>The personal submersibles mailing list complies with the US
Federal
>CAN-SPAM Act of 2003. Your email address appears in our
database
>because either you, or someone you know, requested you
receive messages
>from our organization.
>
> If you
want to be removed from this mailing list simply click on the
>link
below or send a blank email message to:
>
removeme-personal_submersibles@psubs.org
>
>Removal of your
email address from this mailing list occurs by an
>automated
process and should be complete within five minutes of
>our server
receiving your request.
>
>PSUBS.ORG
>PO Box 311
>Weare, NH 03281
>603-529-1100
>
************************************************************************
>************************************************************************
>************************************************************************
>
>
************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003. Your email address appears in our database because
either you, or someone you know, requested you receive messages from our
organization. If you want to be removed from this mailing list simply
click on the link below or send a blank email message to:
removeme-personal_submersibles@psubs.org Removal of your email address
from this mailing list occurs by an automated process and should be
complete within five minutes of our server receiving your request.
PSUBS.ORG PO Box 311 Weare, NH 03281 603-529-1100
************************************************************************
************************************************************************
************************************************************************
************************************************************************
************************************************************************
************************************************************************ The
personal submersibles mailing list complies with the US Federal CAN-SPAM Act
of 2003. Your email address appears in our database because either you, or
someone you know, requested you receive messages from our organization. If
you want to be removed from this mailing list simply click on the link below
or send a blank email message to: removeme-personal_submersibles@psubs.org
Removal of your email address from this mailing list occurs by an automated
process and should be complete within five minutes of our server receiving
your request. PSUBS.ORG PO Box 311 Weare, NH 03281 603-529-1100
************************************************************************
************************************************************************
************************************************************************