O2 analyzer question

[Bill51]

Since the meter on an O2 unit is nothing more than a simple voltmeter I was thinking about building one so I could incorporate a simple voltmeter/battery tester and ohmmeter into the case and make it a multifunction tool. For anyone who has built the El Cheapo, does it look fairly easy to make this modification?

 

[RichKirby]

Thanks for the link! I may have to get one of these things. Do you need any special tools to assemble it? Also, do you need any of the accessories listed on their site to use it once it is put together? Thanks again.

 

[ClayJar]

You need a soldering iron (cheap pencil kind is fine). Some desoldering braid is nice, too, for removing the one resistor (as, I believe, you still must do). Other than that, you need whatever you want to use to make the holes in the plastic case (a butter knife and a lighter would probably work, but other ways are probably better).

If you want to connect it to a standard BC hose, you'll want the $34 tubing-with-adapter gadget. (I prefer that method, myself.) The $5 metal sensor saver cap is a luxury, perhaps, but $5 is pocket change, and if it makes the sensor last longer (or protects it from an unexpected poke), it'd be worth it. I decided to pick up both of those.

 

[pescador775]

Mark, the sensor thread is metric. A plumber's or hydraulic coupler with 3/8 npt will make a loose fit and good enough. Drill two, 1/8 holes in the fitting. After hooking up, turn on the tank valve until a slight "hiss" is exiting the holes. That's all you need to make a reading. Give the calibrated meter a few seconds to stabilize before recording the number.

 

[rjack321]

Since the meter on an O2 unit is nothing more than a simple voltmeter I was thinking about building one so I could incorporate a simple voltmeter/battery tester and ohmmeter into the case and make it a multifunction tool. For anyone who has built the El Cheapo, does it look fairly easy to make this modification?

Sorta, you remove a hard wired resistor on the PM128 board and insert the rheostat. So you'd need a seperate switch to toggle back to the original resistor size.

You would also need an independent way to have two voltmeter leads coming off, and these would need to not short out when you are trying to measure O2 via the sensor.
The connections to the sensor need to be firm and not varying (not leads you're holding to the sensor by hand). The reason being that slight variations in current flow will be reported as O2 percentage changes. The O2 sensor itself is basically a weak battery.

Since an O2 analyzer is life support equipment, I suggest just building a dedicated analyzer. That way you are less likely to mis-measure something and think its an O2 percentage when its just all set wrong. That could be a grievous mistake.

 

[PharmDMark]

I've always used the large blue T adapter and that works fine. I can get accurate readings by holding it over the tank outlet with a slow bleed, or even directly from the second stage mouthpiece. All you have to do is put a steady flow of the test gas past the sensor. Try it on a previously analyzed cylinder and it'll make you more confident. Pressurizing the sensor is not good.

Thanks for all the input

After reading this, I'm curious if anyone else has a simple method for reading directly from the tank valve?

 

[pescador775]

You could make a dome port. Screw together a coupler with round cap, PVC stuff, I guess. Drill the dome with a #60 bit and port the coupler as above, with 1/8 hole. The big concern is to not allow any high flow or pressure build up on the sensor. The flow over the sensor must be very low. This is difficult to control with some tank valves. SMALL inlet port.

 

[ageddiver]

After reading this, I'm curious if anyone else has a simple method for reading directly from the tank valve?

Sorry, that's what I meant by "tank outlet". Pretty soon I'll be calling it a "tank thingy".

Hold the T fitting next to the valve and crack the valve until you've got a steady flow - I'll hold a finger over the open end of the T to partially block the opening and prevent air from entering. But I've always gotten an accurate reading. You can't get any more simple than that. IMO those special adapters are unnecessary unless you've got Parkinson's disease.

 

[ClayJar]

IMO those special adapters are unnecessary unless you've got Parkinson's disease.

They also work quite nicely on a vigorously bucking boat. They're still not "necessary", of course, but every once in a while, I splurge on little luxuries.

(Of course, the tank T style will work for *anyone*, without leaving out the guy with the inflator-mounted secondary with a non-standard fitting.)

 

[pescador775]

This is a bit off topic but here goes: When you decide to convert your perfectly good analyzer into a flaky multimeter you may as well hie over to Radio Shack for some bits and pieces. One of the thingies you may need is a variable resistance gizmo. If you ask for a "rheostat", what you are actually offered may depend on the age of the clerk. A young guy may mistakenly direct you to their collection of potentiometers and you will be gold. An old guy may pull out a collection of actual rheostats which won't work for you. A potentiometer is a resistor with a wiper and simply varies resistance by turning a knob. Generally, these are used for low current DC applications. A rheostat is a reactance device which contains some more complex circuits and works only with AC. The two are not interchangable. The "pot" dissipates a lot of energy (heat). The rheostat loses very little energy, does not heat up because it contains little resistance. That is why the rheostat is used for home light dimmers, etc. It won't burn your house down.