3 sensor PP02 meter

OK, Divers: Version 1 of the 3 sensor PP02 meter was as good as I could do with a lathe, but no milling machine. It works fine. But I KNEW that I could do better, and all it cost me to make it was $4000. That's the cost of a Bridgeport milling machine with enough tooling to make it worthwhile. That, and a few hours spent making large pieces of Delrin and Aluminum into little ones. Here's the project!

The goal was to make a 3-sensor PP02 meter that fit into a Draeger P-Connector. Here's the end result, which is something that you cannot buy in any store. It's exactly what I dreamed of making, and it sure took enough work. In fact, it was the desire to have this that prompted me to buy a milling machine. Now that I have the machine in the shop, no billet of aluminum is safe.

The first half of the project was to make a 3 sensor probe that would place sensors into a Draeger P-Connector, also known as an Oxygauge-Port. If you saw the first edition version that I made, you'll remember that I used Molex connectors and oriented the sensors with their faces parallel to the port. This time I used a solid rod of Delrin, machined accordingly, and oriented the cells perpendicular to the port.

Here's the view of the 3 sensors, showing the wiring. I decided to eliminate all possible points of electrical failure, and directly soldered the sensors to the wires. It may take a soldering iron to change them, but it's absolutely reliable. The three set-screws that you can see hold the sensors into the Delrin rod.

You can see here how I machined the rod flat on two faces, to provide clearance for the sensors.

Here's the end that plugs into the P-Connector. I used a waterproof strain-relief to pass the cable into the probe.

Here's what took the real work. This is a machined aluminum case, made from a solid billet of 6061 aluminum, with a 3/8 inch Lexan lens. It's O-Ring sealed, has an internal battery, 3 displays, and is a work of art if I do say so myself. It ought to be, as it's the third one that I made, and the first one that satisfied me. It's been in my pressure pot to 300 feet for a day and has not leaked a drop.

Wiring is passed through the strain relief, and then is soldered directly to the circuit board. The battery is also soldered directly to the board, with no on/off switch. This makes it 100% reliable, and to turn it off you just remove the battery. With the low power requirement of the displays, I estimate a 6 month battery life if it's left on, so that's not an issue.

For scale, here it is in my hand.

I installed a ring at one end to provide a place to snap the thing to my harness. You can see how I offset the strain relief to accommodate the ring.

Here's the probe being placed into a P-Connector that's been installed into one of my rigs.

And last, but not least, here's Franken-Son with it's electronics: the 3-sensor display for primary monitoring, and the VR-3 (with it's own sensor) for secondary PP02 and decompression calculations.

That's it for this project, which is easier said than done. I estimate that I have a full week of 10 hour days into this. Much of that is due to the learning curve, and also due to my desire to have this be a work of art as well as a utility tool. The circuit board was purchased from Mark Monro, who sells his excellent electronics kits on his website. I'd suggest that anyone wanting to have such a display first get the parts from Mark, and then figure out how to house it. This is the most difficult way, the Lexan tube method being far easier and producing a nice display in it's own right.

		The goal was to make a 3-sensor PP02 meter that fit into a Draeger P-Connector. Here's the end result, which is something that you cannot buy in any store. It's exactly what I dreamed of making, and it sure took enough work. In fact, it was the desire to have this that prompted me to buy a milling machine. Now that I have the machine in the shop, no billet of aluminum is safe.
		The first half of the project was to make a 3 sensor probe that would place sensors into a Draeger P-Connector, also known as an Oxygauge-Port. If you saw the first edition version that I made, you'll remember that I used Molex connectors and oriented the sensors with their faces parallel to the port. This time I used a solid rod of Delrin, machined accordingly, and oriented the cells perpendicular to the port.
		Here's the view of the 3 sensors, showing the wiring. I decided to eliminate all possible points of electrical failure, and directly soldered the sensors to the wires. It may take a soldering iron to change them, but it's absolutely reliable. The three set-screws that you can see hold the sensors into the Delrin rod.
		You can see here how I machined the rod flat on two faces, to provide clearance for the sensors.
		Here's the end that plugs into the P-Connector. I used a waterproof strain-relief to pass the cable into the probe.
		Here's what took the real work. This is a machined aluminum case, made from a solid billet of 6061 aluminum, with a 3/8 inch Lexan lens. It's O-Ring sealed, has an internal battery, 3 displays, and is a work of art if I do say so myself. It ought to be, as it's the third one that I made, and the first one that satisfied me. It's been in my pressure pot to 300 feet for a day and has not leaked a drop.
		Wiring is passed through the strain relief, and then is soldered directly to the circuit board. The battery is also soldered directly to the board, with no on/off switch. This makes it 100% reliable, and to turn it off you just remove the battery. With the low power requirement of the displays, I estimate a 6 month battery life if it's left on, so that's not an issue.
		For scale, here it is in my hand.
		I installed a ring at one end to provide a place to snap the thing to my harness. You can see how I offset the strain relief to accommodate the ring.
		Here's the probe being placed into a P-Connector that's been installed into one of my rigs.
		And last, but not least, here's Franken-Son with it's electronics: the 3-sensor display for primary monitoring, and the VR-3 (with it's own sensor) for secondary PP02 and decompression calculations.