----- 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
>>
>>
>>
>>
>>
>>
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>>
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