Hello Brad,
We could continue this point by point debate forever, so I'm just going to make a few key observations.
You place great faith in the CE / client testing process and seem to be confident that it covers the issue I am concerned about. As far as I can see it does not. You seem incapable of accepting that the CE testing process would not cover every conceivable issue of potential importance, but I suspect that those responsible for it did not even think of this problem. In saying this I mean no disrespect; this is a very new field for CE testing. There are probably many areas in which it could be improved for new monitoring technologies in rebreathers, and it will take them a long time to get it exactly right. I should also say that testimonials to apparent appropriate operation from you and the tiny number of other users currently in possession of these units (or the commercial ones) are completely irrelevant to this debate.
I have no problem accepting that the DL CO2 sensor has been found to accurately measure PCO2. In other words, if you expose it to gas containing 5kPa of CO2 then it will read 5kPa. For the reasons we have pointed out this is different to it accurately reflecting the CO2 levels in the diver. There is much discussion of a complicated processing algorithm that will allegedly achieve this. A simple experiment similar to ours with the addition of recording what the pod says too would tell us whether it actually works, and I cannot believe it has not been done. Maybe it has, but no data have been released. Why not, especially in the face of the current controversy? You seem comfortable to dismiss the problem because “the only controversy seems to be generated by you et al ”, but here is reality Brad: DL are about to release a life support system with a crucial innovative feature. Context area experts have identified potential limitations in this feature and have published their concerns in a peer reviewed paper in the scientific literature. That’s a heady mix. I hope DL have got it right.
Just to provide perspective on this for readers who are fond of quoting me as saying the Apoc CO2 measurement system does not work. This is not what we have said. We have tested their configuration using non-Apoc components and found, as predicted in a debate with Alex Deas almost 2 years ago, that there are potential inaccuracies when the diver is taking shallow breaths. Our work actually suggests that the system will work under most circumstances (when larger breaths are taken). Nevertheless, in a life support product, especially one that bases autobailout on the relevant data, it needs to be right under virtually all circumstances that could conceivably arise. At present, it is not clear to me that this is the case. I am looking forward to getting a chance to test it, and I can’t work out why Brad has been prevented from providing his unit so we can do this.
Simon M
We could continue this point by point debate forever, so I'm just going to make a few key observations.
You place great faith in the CE / client testing process and seem to be confident that it covers the issue I am concerned about. As far as I can see it does not. You seem incapable of accepting that the CE testing process would not cover every conceivable issue of potential importance, but I suspect that those responsible for it did not even think of this problem. In saying this I mean no disrespect; this is a very new field for CE testing. There are probably many areas in which it could be improved for new monitoring technologies in rebreathers, and it will take them a long time to get it exactly right. I should also say that testimonials to apparent appropriate operation from you and the tiny number of other users currently in possession of these units (or the commercial ones) are completely irrelevant to this debate.
I have no problem accepting that the DL CO2 sensor has been found to accurately measure PCO2. In other words, if you expose it to gas containing 5kPa of CO2 then it will read 5kPa. For the reasons we have pointed out this is different to it accurately reflecting the CO2 levels in the diver. There is much discussion of a complicated processing algorithm that will allegedly achieve this. A simple experiment similar to ours with the addition of recording what the pod says too would tell us whether it actually works, and I cannot believe it has not been done. Maybe it has, but no data have been released. Why not, especially in the face of the current controversy? You seem comfortable to dismiss the problem because “the only controversy seems to be generated by you et al ”, but here is reality Brad: DL are about to release a life support system with a crucial innovative feature. Context area experts have identified potential limitations in this feature and have published their concerns in a peer reviewed paper in the scientific literature. That’s a heady mix. I hope DL have got it right.
Just to provide perspective on this for readers who are fond of quoting me as saying the Apoc CO2 measurement system does not work. This is not what we have said. We have tested their configuration using non-Apoc components and found, as predicted in a debate with Alex Deas almost 2 years ago, that there are potential inaccuracies when the diver is taking shallow breaths. Our work actually suggests that the system will work under most circumstances (when larger breaths are taken). Nevertheless, in a life support product, especially one that bases autobailout on the relevant data, it needs to be right under virtually all circumstances that could conceivably arise. At present, it is not clear to me that this is the case. I am looking forward to getting a chance to test it, and I can’t work out why Brad has been prevented from providing his unit so we can do this.
Simon M