How accurate should of a digital gauge is needed for PP mixing?

[Jimmer]

I'm making a mixing whip, and have been looking into gauges. I've been looking at both analog and digital gauges and I'm curious what is considered the minimum accuracy for a digital gauge. I've been looking at a 0.25% FS and 0.5% FS gauge, and was thinking the 0.5% digital must be at least as accurate as a decent analog gauge.

Any thoughts from more experienced mixers out there?

Thanks,
Jim

 

[Whitelightnin]

The .5% FS will do everything you need. Mixing is as much art as science. You will learn you have to have a "fudge" factor in your mixing & that depends on your particular "style". It won't do any good to have a gauge that is accurate to .0001% when your fudge factor is "between 20 & 35 psi for O2 and between 200 & 300 psi for air".

 

[Mako Mark]

If you can consistantly get within half a percent with pp blending you are doing pretty good. There are so many variables.

 

[Jimmer]

Sounds good guys, I guess the next step is make some calls and get some O2 on the way here. What's the general consensus about welding versus medical O2? We only have one place locally that can provide medical, and 3 that are much closer that provide welding.

 

[fppf]

Jimmer
Looks like you have some threads going here.
I would strongly suggest you buy the oxygen hackers book. Also get some first hand training. Dealing with high pressure O2 can be very dangerous if the correct steps are not taken.

And there is no "Fudge" factor in blending if you do the correct math that includes all the variables and you track them. Most of my mix is with in .1% highest error is .25% with no correction. Most people use ideal formulas that don't even include temperature, there "fudge" factor is normaly to cover temperature changes and errors in gauges.

 

[Jimmer]

Well I already have the Oxy Hacker's book and have read it cover to cover and keep referencing it. I mix all my own Nitrox currently under the supervision of my shop owner at the store, since I am a DM candidate with them, they have me do all my own (and a lot of other's) tank fills and mixes for practice. It really just comes down to them being very much a recreational shop, and if you look at their Nitrox mixing logbook, it's pretty much confined to me and one other customer. They only keep one bottle on hand and there have been many occassions where I couldn't get the mix I wanted, because their cylinder was too low. I can't fault them for that since like I said, they are a recreational shop with very little Nitrox. So my instructor and I have been discussing me getting a small 2 or 3 bottle O2 cascade at home, doing the O2 part of the mix at home, then taking the cylinders to him to top them off, that way I have control over my mixes. I appreciate the suggestions as far as safety goes, since that is obviously a top concern of mine, hence why I seek the experience of others on here.

Thanks,
Jim

 

[Mako Mark]

Sounds good guys, I guess the next step is make some calls and get some O2 on the way here. What's the general consensus about welding versus medical O2? We only have one place locally that can provide medical, and 3 that are much closer that provide welding.

You might want to investigate aviation oxygen as an alternative supply, aeroplanes need lots of the stuff and it is the highest grade and I have heard (on this board) that it is often it is cheaper than medical 02.

 

[texdiveguy]

OP--- Aviation grade is very dry 02. Welding vs medical grade is all in the processing of the storage cylinders that you are provided by your supplier.....on medical 02 the cylinders are drawn dry via a vacuum process prior to filling....welding is not. Medical grade 02 imo is the way to go for sure. Besides reading the books,,,you might consider a formal blenders course.

 

[dumpsterDiver]

aviators oxygen always worked fine for me...