Nitrox stick: Measuring after compressor

[estresao]

HI everyone,

I have already made my nitrox stick and I've been using it for a while and once I got used to everything my mixes are pretty accurate..... until nowadays.... In my country (Spain) a famous saying goes "if it works... don't touch it"...... but I did... I touched it.

Well, this was in the aim to get more accurate measurements to reduce mental adjustments. I've had constructed an O2 analyser using an ESP32 processor collecting values from two cells: in the future I want to mix trimix, but so far I'm measuring twice the nitrox to compare and fine tune.

I'm using a static mixer which diameter is 40mm, and I have to reduce de diameter to 20mm which is the inlet of my Bauer PE-100, which can do 100 litres per minute. To measure I'm using an used rebreather cell and a brand new Vandagraph O2 Sensor R-17VAN (which is the same my Vandagraph Tek-Ox uses so I'm expecting having very similar results)

I have not found yet a place where my cells (mainly my Vandagraph O2 Sensor R-17VAN) reads accurate values... sometimes I've got similar, but not good enough and I end up making mental calculus. My guessing is that gas flow is too much for the cell, which seems to "work with a flow rate between 100 millitres per minute to 2
litres per minute" (SIC from Vandagrash site)

I've tried in different ways:
1) mounting a 40mm PVC T after the mixer and locating the cell in the side branch.... including these variants:
1.a) Located in a PVC lid using a Flow Divertor (9711000)
1.b) same than before but with no flow divertor
1.c) attached one more PVC T and located the cell and flow divertor in the 2nd T side brand in vertical
2) Mounted 20mm PVC T after the reduction from 40mm mixer and right before the hose to the compressor.

My next tries are following options:
1) Setting a bypass from the 40mm section to the 20mm section to get some Venturi effect and locate in that bypass the O2 cell and a flow reducer
2) Same than 1 but connecting to the bypass to a Vandagraph Quick-Ox Sampler (Reference 9730210) which is the same my analyser uses


Those who made similar sticks, are you guys getting accurate values?

 

[estresao]

After running some test I still cannot get proper measurements from the cells located in my stick. I managed to add a bypass with venturi effect to control the flow crossing the O2 cell.... but even controlling that never got proper values.

I managed to use both, my home made analysed based on an ESP32 microcontroller and directly using my pocket analyser i both case using exactly the same O2 cell... while my pocket analyser provided lower values compared to when I measure directly in the tanks, the ESP32 based was even worse, so I'll get a commercial analyser to add to my stick.

I've got two questions for those who are using commercial analysers
- Are you getting proper values? (I know there would be around 0,5% because the humidity difference)
- Where and how have you installed it?
- Are you using a flow divertor? Like this one: Flow Divertor (9711000)

 

[clownfishsydney]

I could never get accurate results from the stick, so I just did some sampling of the final result in tanks and worked out a graph showing % Nitrox from various oxygen regulator psi. I can get to half a percent every time.