Reliable CO2 sensor. How far are we to achieve that in diving applications?

[WOB0.01J]

I have been using my se7en for about 2 years now, and been enjoying diving it so far (about 35 dives in with a lot of ups and downs). I have been thinking about moving towards the M28 and solid-state sensor in the near future since SSS is having excellent track record as for right now. ( I just dive the paddle right now, and it has served me well )

From said that, what exactly is the difficulty to achieve a reliable CO2 sensor technology? How far are we until we reach this point? IMHO SSS sensors are reliable as it is plus CO2 sensor would probably make CCR divers' way more confident about the dive. Because a CO2 hit is probably the most frightening part with rebreathers.

 

[Josh the diver]

for my understanding the problem is humidity in the breathing loop. water vapor gets mistaken as co2.

 

[WOB0.01J]

for my understanding the problem is humidity in the breathing loop. water vapor gets mistaken as co2.

Interesting! I did not know that.

 

[Josh the diver]

on gue tv there is a recording from rebreather forum 4 called developments in co2 monitoring by Simon Mitchell.

 

[philkenobi]

Here it is: Rebreather CO2 Monitoring: Impact on CCR Diver Safety

 

[grantmac]

Lungfish apparently have this cracked:

Grokking Lungfish’s Orca V6

Rebreather instructor trainer Dave Gration takes us for a dive into one of the newest breathers on the block, the Lungfish Orca V6, which attracted lots of attention at Rebreather Forum 4. Gration, who is a factory trainer for the unit reviews its innovative features including its compact...

indepthmag.com

 

[Snusmumrik]

Interesting! I did not know that.

Common CO2 sensors are NDIR. CO2 molecules absorb specific wavelengths of infrared light,
thus resulting in less light reaches sensor as more CO2 molecules present in surrounding air.
Water vapours also absorb same specific wavelengths of infrared light, affecting measurement.
Also, NDIR sensors are somewhat slow, 30 seconds for measuring cycle is a huge
amount of time in rebreather application, and some sensors are more slow, up to minutes.

 

[OTF]

Lungfish apparently have this cracked:

Grokking Lungfish’s Orca V6

Rebreather instructor trainer Dave Gration takes us for a dive into one of the newest breathers on the block, the Lungfish Orca V6, which attracted lots of attention at Rebreather Forum 4. Gration, who is a factory trainer for the unit reviews its innovative features including its compact...

indepthmag.com

"Though how it works is a closely-guarded secret, Lungfish claims that the sensor correctly distinguishes CO2 from water vapour/moisture or other gases in the loop eliminating false alarms and or false positives. [Ed. note: Lungfish has not specified the sensing technology they are using]"

That's quite a choice to make in this field.

It's promising to hear that whatever it is might actually work though!