Co2 Sensor At Dema

RZEP17

Somebody mention a few CO2 sensor presentations at this year DEMA.
Unfortunately I could not make it.
Anybody have some more info on the subject?
rgrds
Tomek

decoweenie

It was discussed in the DEMA thread since I asked the same question earlier.

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RZEP17

Yes I've read that! I was hoping for more detail info on the principals - if this is no secret.
t

diverklondike

You had to be there...

Not sure if Tom Rose is sharing the details outside of the live presentation...

Dive Safe

Mark

Tom Rose

Hi All,

For those who did not go to the rebreather party at DEMA or could not hear well, here is a summary of my presentation on CO2 monitoring.

First a few facts......

Non Dispersive Infra Red is the only direct instrumental measurement of Carbon Dioxide. The US Navy recognized this many years ago. I have been using NDIR analyzers professionally since 1970 and made improvements in them that manufacturers have incorporated in their designs.

HOW WE TRAVELED TO DEMA AND BACK AND HAD A LOT OF FUN IN THE PROCESS.

In a casual conversation at DEMA 2003, someone said you could not use IR in rebreathers because of the condensing gas stream.

I blurted out, “That’s silly.” Then I shut up. Within a short time I filed a provisional patent application for a system allowing NDIR use in rebreathers, solving the problems of a saturated condensing atmosphere after the scrubber.

At DEMA 2004 I shouted about it but no one was really interested...

Not the Navy, Not the industry, No rebreather manufacturers
And as usual my wife was already spending the money from the idea. She is damned good at that.

This was followed by a Utility Patent Application...I was really starting to spend money...

I have already described the basics of my idea in a previous article in RW. So I will not bore you with those details.

In essence, I simply solved the condensing gas stream problem. I was going to use an off the shelf CO2 monitor...first big mistake....after extensive negotiations with manufacturers who at first were very excited fell apart when they learned the pressure in the cell could easily exceed 150 PSI....I was left with no monitor...I had to build my own CO2 monitor...that set me back on my time line...but really improved the instrument in terms of size, price, and durability.

I built several and did some lab testing to learn the following:
Does it really measure CO2?--------Answer yes
Does it Calibrate------Answer yes
What about pressure---------The cell did not seem to have any problems in the lab...but you know that the lab is always kinder to instruments than the outside world...especially the underwater world.

I considered a number of rebreather test beds for in water testing....and rejected all of them...
My first thought was keep it simple...but I rejected my 100 dollar rebreather as how could the Navy respect testing using a rebreather equipped with a hot water bottle. Hell that rebreather was a joke when I designed in 61.

100 DOLLAR REBREATHER

I considered my Italian Cressi, but felt the Brits wold not like my using a system that had caused them so much trouble in WWII..

http://www.atlimp.com/classicconvertible.pdf

..I did not have a Mark 16 and there would be problems trying to retrofit into the space in most commercial rebreathers, how would I do the display, units are not available and there was the time and training problem. Also, I saw that I could lose control of the process.

So I rolled my own rebreather In what I call a standard pattern, you know...Two tanks, Scrubber on the back, Over the shoulder counter lungs, space for the CO2 monitor...cost me a little more time, but in the long run was well worth it....

Testing was going to be for Durability, Depth, Temperature, Shock, and eventually flooding

Besides a pool, which is not much better than a laboratory, I planned in water tests...I selected CoCo View on the island of Roatan....

I had been diving there since 91 and they had been particularly helpful in the past with oxygen supplies for my rebreathers. The water is warm, the water is clear, I could easily dive to the depths I needed to test at, a week of diving is reasonably inexpensive. I could get in some great diving and accomplish all I needed.

I took along Robert Bradish as my support diver. Although Robert is in his 40s, he has been diving 30 years. Robert has been a support diver on Andrea Doria, he was starting to really get interested in rebreathers, had never been to the tropics, was young, strong, healthy, and could go on a moments notice...You will be hearing a lot about Bradish in the coming years....in less than a year of interest in rebreathers he has designed and built his own design SCR and collaborated with me in the design of a fantastic up-gradable rebreather system and a novel DSV with and without OC Bailout options.

We hit Roatan in October so we could go to DEMA with some testing under our belt...Little did we know....

My plan was to do the preliminary tests in about 130 or so feet of water.....you know crawl before you walk....The first casualty of an operation is the plan....We dropped a little below 130 feet and then I accidently flooded the optical cell with salt water. Oh *&^*, I thought, then I realized that this was an opportunity. Bradish really looked worried..I simply came to the surface, left the cell flooded for 4 hours, rinsed it out with water from the rooms drinking water bottle, packed it away and we continued to dive OC. and rebreathers for the rest of the week. This is hard work you know.

The soggy monitor sat in the package for over a week before I could get to it when we got back. I rinsed it out with distilled water, then absolute alcohol (not absolute vodka) and started testing it. It calibrated perfectly....

I was ready for DEMA.....at DEMA I showed the cell to a number of persons, made a presentation at the party, and enjoyed demonstrating that it could be thrown on the flow, against walls, in fact, it was probably the only instrument that was tougher than Leons Megs. I doubt they would survive a two story fall but my cell will.

What’s next. It has now been tested to 150 feet in a pressure pot (as deep as mine will go) and I have been working on a unit that can handle at least 300 feet. Gene Melton has offered to test on in his pressure pot to 500 feet.

My target date of availability of a commercial system is Spring of 2007....

Here is a picture of the cell

http://www.atlimp.com/cell.jpg

A few specifications

Monitor output is 50 mv for a CO2 level of 5% making it compatible with O2 cell displays.
Power usage is 25 Milliamps

I have designed a retrofit package for any rebreather with over shoulder hoses.

No living animals or birds are used in the monitor.

Bazza

Put me down for a couple and if you want a crash dummy in Oz let me know!

regards Baz

rdmmdr

i want one
rick

jaap

[quote=Tom Rose;82703]
Monitor output is 50 mv for a CO2 level of 5% making it compatible with O2 cell displays. Power usage is 25 Milliamps

I have designed a retrofit package for any rebreather with over shoulder hoses.
quote]

Nice thing! Do you have any pics of the whole thing including the gasdrying parts?

I guess the output is proportional to the concentration of CO2? So that it reads in %-CO2?

Or is the output affected if the %-CO2 is constant but the pressure is changing?

The thing I'm after is that I guess a diver would like to have the display giving pCO2 or SEV-CO2 conc.

So is it also necessary to incorporate at pressure sensor to get an easy to interpret CO2-level reading?

__________________
My initials: JAAP

Genesis

I want one too.... and guess what - I've got a few unused ADC input channels on the K1's head board

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http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Tom Rose

[quote=jaap;82782] A NDIR system "counts" the molecules of CO2 in the gas path....the greater the number of CO2 molecules the less signal to the detector....the number of molecules in the path is due to a combination of proportion of CO2 and pressure. Regardless, you cannot tolerate but so high a percentage of CO2 molecules in the gas mix reported as if it was at the surface.

Therefore it does not care about pressure or concentration. It just tells you the absolute amount of CO2 in the IR path.

Just like oxygen....pure oxygen at the surface is not a real problem to breath....but take that pure oxygen to 100 feet and we have a problem...houston control

We certainly do not want to breath CO2 levels of 5% at the surface or at 130 feet breath 1% CO2. Fortunatly properly working scrubbers keep the CO2 at lower and lower percentage as depth increases.

Hope this helps,
Tom