O2 Analyzer Calibration

[WetDawg]

OK, just finished building the $90 O2 analyzer from RC Tech.

Went together easy and looks great. Only one "small" issue is that I have not been able to figure out how to set the initial calibration. Yes, the knob on the potentiometer is dialed all the way down and still reads 41.0. Also, I have dialed down the internal screw on the PM128 board as well - I watched it go down from 55.2 down to 41.0 but still will not go lower.


Do any of you mad scientists out there have any suggestions? Thoughts? Comments?

 

[espenskogen]

OK, just finished building the $90 O2 analyzer from RC Tech.

Went together easy and looks great. Only one "small" issue is that I have not been able to figure out how to set the initial calibration. Yes, the knob on the potentiometer is dialed all the way down and still reads 41.0. Also, I have dialed down the internal screw on the PM128 board as well - I watched it go down from 55.2 down to 41.0 but still will not go lower.


Do any of you mad scientists out there have any suggestions? Thoughts? Comments?

Try taking the analyzer out of the hyperbaric chamber, and blow some normal air through it?

no, kidding - Sounds like you have a somewhat inaccurate analyzer on your hands

E

 

[The Chairman]

Sounds like a call to RC Tech is in order... that or time for some percussive maintenance!

 

[Mark Vlahos]

OK, just finished building the $90 O2 analyzer from RC Tech.

Went together easy and looks great. Only one "small" issue is that I have not been able to figure out how to set the initial calibration. Yes, the knob on the potentiometer is dialed all the way down and still reads 41.0. Also, I have dialed down the internal screw on the PM128 board as well - I watched it go down from 55.2 down to 41.0 but still will not go lower.


Do any of you mad scientists out there have any suggestions? Thoughts? Comments?

I have an analyzer that I built from RC Tech a couple of years ago. At least on my analyzer there is no "initial calibration" at least not a calibration that is separate from the calibration you need to do each time you use it.

To calibrate it simply hook up the analyzer in exactly the same manner that you will hook it up when you want to analyze a tank of NITROX with the lone exception that you need to hook it up to either a cylinder of normal compressed air or oxygen, the type of gas you use will depend on the final blend of NITROX you intend on testing and the limitations of your training and equipment.

Without the sensor plugged in to the analyzer you will get random readings on the display that mean abloslutely nothing so ignore them. Once you plug the sensor in to the analyzer it may take only a few seconds or a few minutes for the reading to stabilize, once the display has settled down you can turn the dial to make the number match the known gas you are analyzing. Once you have "set" or "calibrated" your analyzer in this manner switch the gas to the cylinder you need to analyze and read the display. You need to be very careful that once you have calibrated your analyzer on the known gas you must not touch the adjustment dial or turn off the machine before you test your NITROX cylinder. You need to calibrate the analyzer before each session of analyzing breathing gas, if you turn it off and put it in a box or bag you must calibrate it again.

Mark Vlahos

 

[amascuba]

OK, just finished building the $90 O2 analyzer from RC Tech.

Went together easy and looks great. Only one "small" issue is that I have not been able to figure out how to set the initial calibration. Yes, the knob on the potentiometer is dialed all the way down and still reads 41.0. Also, I have dialed down the internal screw on the PM128 board as well - I watched it go down from 55.2 down to 41.0 but still will not go lower.


Do any of you mad scientists out there have any suggestions? Thoughts? Comments?

I built one from oxycheq a couple weeks ago, but they are essentially the exact same parts. The only thing that may be different are the o2 sensors used. Mine callibrated just fine.

You might double check your wiring, particularly the wiring to the potentiometer and the wiring to the jack that leads to the o2 sensor and make sure that you didn't get the wiring backwards.

Also, you did cut off the built in resistor on the pm128 display with a exacto knife and solder the 300 ohm resistor?

Did any of your solder's over lap into other parts of the circuitry?

If all that's correct then you may have a bad sensor.

 

[RisingPhoenix]

Also, you did cut off the built in resistor on the pm128 display with a exacto knife and solder the 300 ohm resistor?

Or just use tweezers and an iron if your neat.. It bothers me that being electronics by trade has helped in diving

But here, the parts are slightly different, the PM128 is not the same as in the US but close enough to get working!!

Steve

 

[Randy43068]

OK, just finished building the $90 O2 analyzer from RC Tech.

Went together easy and looks great. Only one "small" issue is that I have not been able to figure out how to set the initial calibration. Yes, the knob on the potentiometer is dialed all the way down and still reads 41.0. Also, I have dialed down the internal screw on the PM128 board as well - I watched it go down from 55.2 down to 41.0 but still will not go lower.


Do any of you mad scientists out there have any suggestions? Thoughts? Comments?

Did you get it fixed?

You could try using a different meter (mulitmeter) with a 200 - 300 mV scale to read your sensor. See what it reads with 21% on it.

 

[WetDawg]

The weirdest thing... left it in a pelican box in the truck for a couple days and now all is well. Dials right down to 20.9% for calibration and seems to read accurately.

I did nothing to make this work. :huh:

 

[Sharks Friend]

Looking to build one of these kit O2 analyzers and have heard good and bad bout both types the RC tec & Oxychec? something to do with crappy O2 senors? One not being as good as the other ? Can anyone give some strait info on that ? thanks

 

[amascuba]

Looking to build one of these kit O2 analyzers and have heard good and bad bout both types the RC tec & Oxychec? something to do with crappy O2 senors? One not being as good as the other ? Can anyone give some strait info on that ? thanks

the only thing that you are actually building is the device that reads the output from the o2 sensor. The sensor that comes with the oxycheq is a teledyne sensor which is used in rebreathers and other o2 sensors use the same sensor. the reader is really a simple device. The one thing that you will want to build or buy that doesn't come with the kits is a flow restricter so that you get a nice constant flow to the sensor that doesn't push too much air pressure towards the sensor. Doing that will give a bad reading.