A while ago, somebody gave me a book to read. I have to say, the title of the book didn’t exactly fill me with excitement. Oxygen Measurement for Divers by John Lamb. Whatever – I’d made a promise to read it, so why not.
The title didn’t want to make me read it…
On opening Oxygen Measurement for Divers I discovered that John was a Medical Physicist, and I had followed a very similar career to his. John worked in hospitals, initially designing medical equipment, and then moved on to research based work. He eventually set up Vandagraph, a company now famous for making oxygen analysers for divers. Anyone that has dived nitrox has probably used one of his analysers at some point.
So now I’m more intrigued, what could this book teach me, and would it be interesting at all. I was sure that the science and engineering would be accurate, but as a diver, would it help me. I analyse my breathing gas every time I dive, and I use oxygen monitoring cells in my rebreather. As part of my work, I also teach people how these cells work, and how to look after them. The thought of working through 200 pages of technical data filled me with dread, and I really wasn’t looking forward to it.
But a promise is a promise, so in I went.
John begins by going through the different technologies that are available for measuring oxygen levels. There are many of them, but very few are suitable for diving applications. They are expensive, highly sensitive to movement or calibration, or just need so much skill to operate that they don’t really do well in a diving environment. My favourite technique was is the paramagnetic analyser – would you believe that oxygen is magnetic? It’s the only gas that has this property, and you can use this to measure the oxygen concentration in a gas. Who knew! Sadly, this is one of the sensitive and expensive techniques, so no good for divers.
The best technique is sadly no good for divers…
The method of choice is the galvanic cell. This is the system used in your oxygen analyser, and in a modern closed circuit rebreather. It’s a chemical paste that produced a voltage when exposed to oxygen, The higher the voltage, the higher the partial pressure of oxygen in the gas you’re measuring. Simple.
Well, not so much. Like most chemical reactions, it is sensitive to temperature, and John does a great job of explaining how cells change their output with temperature, and how this can be corrected and accounted using electronic circuits inside the cell. There are other limitations to these cells too, humidity, current limiting, what happens if they get wet. The list goes on, and John deals with them all.
John deals with all of the important aspects of the oxygen sensor
You don’t need a degree in electronics or physics to understand the book at all. John explains all in a very easy going and accessible way. But if you do have that background you won’t be patronized either. I don’t know how he does it – writing like that is quite an art.
By the time you’ve read the first few chapters of the book, you well have an excellent understanding of how an oxygen cell works. You’ll understand what the effect of atmospheric pressure will have on your nitrox analysis. You’ll also understand why you need to change the cells in your rebreather much more frequently than you do with your analyser. If current limited cells were a mystery to you, after an hour or two you will know why it’s a huge danger for rebreather divers, and how you can take simple steps to predict when it happens.
This book explains current limited cells perfectly
I was so impressed with Oxygen Measurement of Divers that I asked John if I could offer them to you. He’s sent me ten copies, and I’m so convinced that you’ll enjoy the book, that I’ll give you your money back if you don’t learn something from it.
Learn something, or your money back.
It’s simple – buy the book and read it within 30 days. If you don’t learn anything, or don’t find it interesting within 30 days, just send it back and I’ll return your money. No arguments. I might ask you why, but I promise I will refund you the cost of the book. And remember, I keep promises.
Secure your no-risk copy of Oxygen Measurement for Divers now using the button below.