Nitrox Stick auto adjusting blender

[rob.mwpropane]

One safety is to set the setpoint to 40 and dial back the o2 regulator to a max of 1-2 PSI above what you are really wanting (eg. 34% for a 32% mix). Then change your setpoint to what you really want. This will provide an upper bound if the proportional control valve gets stuck open. One nice thing about a PID control is that it works off of the error reported between the setpoint and reading. So if the compressor cuts off, and the o2 in the mixer goes up, and up as if it is trying to go to 100%, the proportional valve will keep trying to reduce the o2. Quickly closing the valve and cutting off the o2. I tested this last night. I had the mixer set to 32%. This is an 8 cuft/min compressor. When the compressor shut off, the spike in o2 across the mixer chamber in the nitrox stick only spiked to 35% before the valve closed entirely. A lower-volume compressor would most likely experience less of a spike.

That's awesome!

 

[happy-diver]

Magnificent!

 

[tbone1004]

@The Chairman as requested!

I think it's a cool idea. In reality I don't know how well that it would all hold up over time? I would assume there's some type of fail safe if O2 went too high?

I have read that a lot of people depend on 2 O2 regulators to dial in the flow. This supposedly really helps stabilize the mix.

I'm really close to having my stick up and running... the heat here has brought everything to a halt (and I'm kind of lazy).

It's very cool though. Do you have any videos of it working?

You could also put a normally closed solenoid on the O2 line and have it tied to the e-stop circuit on the compressor so anytime the compressor is off the solenoid closes which is a standard fail-safe for manual sticks

 

[The Chairman]

Now let's incorporate Trimix!

 

[brysonjk]

@The Chairman as requested!




You could also put a normally closed solenoid on the O2 line and have it tied to the e-stop circuit on the compressor so anytime the compressor is off the solenoid closes which is a standard fail-safe for manual sticks

I have considered this. I have the solenoid valve, and a current transducer for it, but never got around to implementing it. Being that I started this project with the desire to get something working for my own system which only gets a few hours of run time monthly, I never really got around to adding too many of the fail-safes beyond what I mentioned above. The plan all along was to get it working, open-source it, and then see where it goes. The average person can't afford a trihunter.

 

[brysonjk]

Now let's incorporate Trimix!

This can be done rather simply. You would need a larger valve than the one that I listed on my GitHub page. Something more along the lines of the link below. The algorithms should still work. They may need to be tuned a bit differently though. My little mini valve tops out at 40 l/m.

High Flow Mini Valve - kellypneumatics.com

This mono proportional valve ensures virtually frictionless performance and longevity tested at over 100 million cycles. Click here!

kellypneumatics.com

 

[The Chairman]

The average person can't afford a trihunter.

You know it's going to be expensive if they don't advertise the price on their website. Do you know the price?

TriHunter 6000 – Advanced gas mixing made easy

www.trihunter6000.com

 

[The Chairman]

What O₂ sensor are you using? What He sensor be appropriate?

 

[The Chairman]

@Serge has created something like this.

 

[brysonjk]

You know it's going to be expensive if they don't advertise the price on their website. Do you know the price?

https://www.trihunter6000.com/[/UR [/

http://

You know it's going to be expensive if they don't advertise the price on their website. Do you know the price?

TriHunter 6000 – Advanced gas mixing made easy

www.trihunter6000.com

$4500 for the base model. Whatever that is.