Disposable CO2 and O2 sensors

AD_ward9

Will we be using galvanic O2 sensors, and dual channel IR absorption CO2 sensing in 10 years time? I suggest not. What will replace it, and how can we make new designs user upgradeable to the new technology?

Other methods include potentiometric sensing, but these tend to require high temperatures. It is clear the winning technology will be sol-gel, probably just ink jet printed onto the end of the cartridge. A suitable light source then just reads the O2 and CO2 concentrations, by measuring either fluorescence or the quenching time of the fluorescence. Replacing the cartridge means replacing the sensors, but as they cost cents, who cares?

O2 and CO2 sensors are even being put on disposable food packaging using sol-gel technology. See http://www.osl.dcu.ie/projects/Intellipak/ and http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract

The response time for some sol-gel optical technologies is about 10 times faster than the best existing sensors. For example work in the University of Southampton has produced a CO2 sensor with 1 second response times. See http://www.spie.org/web/abstracts/2200/2293.html.

There is work all around the world on sol-gels: they are not new technologies, but coupled with nano particles, gives a product which meets the commercial needs.

It is not just CO2 sensors using sol-gel techniques, but also O2: http://www.solgel.com/sgnews/templat...id=32&zoneid=3

So how do we future proof designs? Let us assume the sol-gel will win out over MEMs designs such as http://www.ornl.gov/sci/engineering_..._net_power.pdf
In this case, the module needed to read the sol-gel code can be interchanged with the CO2 sensing module.

In the Deep Life Open Revolution proposal, the scrubber stick would be replaced and a CO2 and O2 sensor reader using the CO2 port would be fitted. The scrubber stick is user replaceable (in fact, if something in it fails, the user can unplug it and the system still works but does not show CO2, He or scrubber health.

In terms of timescales, these sol-gel sensors may come into diving with the next couple of years. The result should be much more reliable O2 sensing, and CO2 sensing without any significant cost premium.

If the fluorescent wavelength is chosen appropriately, there should be no change with depth or pressure, greatly simplifying the task of CO2 sensing in a CCR.

Any better ideas for the future proofing, other than fit the new technology now?

Cheers,

Alex

MichaelS.

I was wondering if there was any progress in this area?

AD_ward9

Slow. First version will use what is posted in the circuit diagrams (galvanic O2, and IR CO2). Sol-gel is probably a 3 year timescale away from being a product anywhere, but by 7 years from now, I would expect it to sweep away the current sensor technology for RBs.

Cheers

Alex

PeteS

Does this mean you would not use a scrubber monitoring system? That you would rely on a CO2 breakthrough monitor alone?

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Pete S.

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RonMicjan

Actually one would design a tap for gas to be tested part way through the stack, like at the 3/4 mark, when Co2 reaches this point an alarm might go off alerting the diver that his scrubber is almost done.

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AD_ward9

The present scrubber stick contains 5 groups of sensors:
1. Scrubber temperature (16 temperature sensors)
2. Pressure (2 sensors, one before, one after the scrubber)
3. He sensor
4. CO2 dual channel IR sensor
5. Temperature sensor in CO2 measurement path

In addition there is a photosensor on the O2 sensor board, which detects when the unit is openned.

The sensors are used for:
A. Scrubber health (Sensor groups 1 and 2)
B. Scrubber life (Photosensor+user question on replacing the scrubber, Sensor groups 1,2,3 to integrate the total heat generated by the scrubber)
C. He in mix
D. PPCO2
E. Respiratory Monitor: Tidal volume, Rate and WOB (Sensor group 2, plus resistance from scrubber)

So, scrubber life as shown on the handset, does not rely on the CO2 sensor at all.

Scrubber health is an exception: it is not displayed until the scrubber is not working correctly: the temperature distribution after compensating for the gas mix and flow parameters, is outside the corridor for that scrubber.

In moving to a sol-gel sensor, one simply replaces the CO2 sensor with the sol-gel CO2 and O2 sensors. Nothing else is affected. No taps are needed.

Cheers,
Alex

robertkarlsson

Found a oxygen sensor with some interesting specs. Even though if this one isnt cut for the job its still an intersting
technology.

From their site:
"The SMSI® Oxygen Sensor, pictured on this page, is a miniature solid-state transducer that uses fluorescence to measure oxygen partial pressure. An LED excitation source and fluorescence detector are both integrated into the device. Key features of the SMSI® Oxygen Sensor include:
Accurate - ±1% of reading (i.e. ±0.2% percentage oxygen in air) using simple, inexpensive drive and detection circuitry.
Fast Response Time - As low as 20 ms response times.
Low Power Consumption - As low as 5 mW at 100% duty cycle.
Highly Specific - Strong response to O2, insensitive to common atmospheric and medical gases.
Long Lifetime - Up to several years for many applications.
Small Size - Just over ¼ inch maximum dimension."

Url:
Oxygen Sensor

teksimple

That looks AWESOME! Other than the output (18mV max but perhaps that is at 20.9% O2), this thing looks totally appropriate for a rebreather. They even mention diving rebreathers specifically for the application. I am going to call those guys to get the scoop. Thanks for the tip!

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nigelh

If you have a disposable cheap CO2 sensor you could stick one 2 inches down the scrubber stack. This would be far more useful than temperature.

In fact have an array and really know what part of the scrubber is working.
Much as I like my Vision temp stick that would blow it into the weeds by measuring what we want to know not a side effect.

__________________
nigelh

Wol

Alex,

I have read much regarding your open revolution approach to rebreather design. What are your current thoughts regarding timescales for launching your rebreather to the sports diving market. Also - do you have any sense of the likely costs of a unit? - If not your own, do you have any views on the timescales that other 3rd parties utilising your designs may be launching poducts?