calibration and pressure test query

spunkmire

Hello,
I have been diving my Inspi Classic for about 30 hours, already sent it back for the craic (fixed FOC) and still enjoying it.
However, I have having some confusion over the cell readings.
When I calibrate, I ignore the actual atmospheric pressure and keep it at 1000mb, my instructor told me not to bother and I don't know how to find out.
The oxygen content I declare as 1% below what I analysed to be in the tank, and I start calibration with the loop squeezed down slightly, mouthpiece closed (until it gets to 50-60%) as this gets the ppO2 up much quicker on bag flushing. Opening the mouthpiece at 50-60% to let the gas out!
Two cells get to 96-98%, with some effort, one cell gets to 94-95% but it looks like the readings are still climbing up (the number flicker like they are on the cusp of changing) when the heads decides "calibrating".

Unit dives well, but when back in the base and the head dry, the cells comminly read 17-19% in air - somehow I am making the unit under-read the cells?

Should I care?

Also, when I look at the displays underwater, they always seems to read .67- .69, or 1.27-1.29 I would prefer them to read .71-.72 and 1.31-1.33 for decompression purposes. Should I care about this ?

Also someone said that air-drying the cells too much is bad for them, the electrolyte dries out or something like that- is that important?

Also, getting the hose to collapse down on a neg test is very difficult, the hoses are very rigid and my lungs are relatively weak. When the hoses do collapse they tend to 'stick' and I never know if it is totally watertight.
I do the test for 5mins max, min. 1min as someone said the low pressure is bad for the ADV (I can see why it would not be good for the connections).
Is this OK?
I read of people complaining that their unit does not hold -ve for less than an hour, I've never done a test for more than eight minutes?

Also, then solenoid is not keeping up with the ppO2 on ascent, is it a good idea to keep adding a bit of O2 (quick tiny O2 add while exhaling) to keep the ppO2 or should I come up slower?
Or simply ignore it? Possibly the dissolved gas movement during ascents is minor compared to the greater movements occurring at the stop depths (due to the greater time spent at the stop, rather than reaching it)- so getting the pO right on the stop is much more important than fussing with setpoint as I move up to it?

Also, what is the best ppO2 for diluent ? I reckon 1 bar on the bottom as this keeps it good for deco, but low enough to flush effectively.
Am contemplating 10/52 for a clear head past 30m but it makes dil flushes a massive swing and consequently more effort to get back to SP?
Is any heliair a good idea, e.g. 14/33, as it is just easier to get hold of.

Finally (phew) someone told me to get a voltmeter to keep track of the battery and cells, can you get one that does both and what is the spec. of it- e.g. the voltage/ ampage range? (what do I ask for in the shop)

Any replies welcome!

Cheers

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Totally confused

nigelh

Personal opinions so others may differ (violently).
also I'm not touching everything

Two cells get to 96-98%, with some effort, one cell gets to 94-95% but it looks like the readings are still climbing up (the number flicker like they are on the cusp of changing) when the heads decides "calibrating".
Are you sure you're talking % not the voltage?? The thing goes into "Calibrating" when it thinks the O2 levels have stopped moving not when it reaches some magic number.

Also, when I look at the displays underwater, they always seems to read .67- .69, or 1.27-1.29 I would prefer them to read .71-.72 and 1.31-1.33 for decompression purposes.
I would care if my rebreather say 1.3 and still decided to inject O2. It must always be hunting to catch up with your usage so 1.28 is good. If you want it higher set it higher but few of us bother.

Also someone said that air-drying the cells too much is bad for them, the electrolyte dries out or something like that- is that important?
They are rated 0-99% humidity so that might be news to Teledyne. Leaving them dripping wet probably doesn't do them much good. I pop the top and when it's dry clip it back down to stop the fill scrubbing the atmosphere.

Also, getting the hose to collapse down on a neg test is very difficult, the hoses are very rigid and my lungs are relatively weak. When the hoses do collapse they tend to 'stick' and I never know if it is totally watertight.
I do the test for 5mins max, min. 1min as someone said the low pressure is bad for the ADV (I can see why it would not be good for the connections).
Heck if it just tries to hold pos or neg I'm happy. We're only testing for holes and things not done up. I'm going to stuff a open gap in the loop into my mouth and I leak like a sieve and I must be maintained at ambient. Some people like to quote hours of pressure test but I'm not convinced that is what the tests are all about and it probably trashes the ADV diaphragm given time.

Also, then solenoid is not keeping up with the ppO2 on ascent, is it a good idea to keep adding a bit of O2 (quick tiny O2 add while exhaling) to keep the ppO2 or should I come up slower?
Well slower is better but for different reasons. On the ascent it is throwing O2 into the loop and you are dumping it back out. Normally we have to warn people to put up with that as people have killed themselves 'saving' O2 by turning the feed off on the ascent so your problem is good and normal.

Also, what is the best ppO2 for diluent ? I reckon 1 bar on the bottom as this keeps it good for deco, but low enough to flush effectively.
Am contemplating 10/52 for a clear head past 30m but it makes dil flushes a massive swing and consequently more effort to get back to SP?
Is any heliair a good idea, e.g. 14/33, as it is just easier to get hold of.
I wouldn't touch a hypoxic mix on a dive that didn't demand it. There are more sad stories we could tell. Personally I think Heliair sucks. It's just a game to get out of analysing helium content. It's normally exactly wrong for any dive. I seem to have settled for 18/40 over the years. I'd like it a bit richer but I do do quite a bit of 60m stuff and it's a weak flush then.

Finally (phew) someone told me to get a voltmeter to keep track of the battery and cells, can you get one that does both and what is the spec. of it- e.g. the voltage/ ampage range?
Since nobody actually agrees how you should interpret the voltages you get buy a cheap digital with a 2V range which is all of them. If you pay more than £10 you were ripped off. Sadly cells don't fade away they just die and voltages in air tell you nothing. Watching the voltages when it is calibrating is normally informative as every cell that has given me trouble before its year was up has gone slow and was the last to calibrate for a while before. Sadly there is always going to be a last cell but being much longer than the others worries me a bit. The voltmeter will be more use to check your batteries. On my classic I wouldn't go in the water for a deco dive unless they were reading 6V when I was setting it up for the day. The Vision checks them under load which is a better trick. I'd rather throw a battery away with some life in it than risk having one wimp out on me.


Oh well. Back to the report I really don't want to write... Thanks for the distraction.

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nigelh

tiggerbiker

just to add to nigels post - which i agree with 100%

if you have only done 30hrs on your unit, your only MOD1? - use air as your dil, wait for MOD2/3 before putting heliair/trimix dil into it.

i have done about the same time as you and i thought i was really getting the hang of it and i wanted to do my MOD2/3 ASAP but i had a few issues on my last dive which thankfully, due to my superb training/instructor, i delt with safely and effectivley but i was a bit of a wakeup call.
i have now slowed down and have put off my MOD2/3 untill i am actually ready, not when i think i'm ready - i'm not trying to lecture you, just passing on my own feelings.
dive safe
Grant

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the more i learn, the more i realize i know nothing

craige

Hi,am not sure why you want to get a much quicker flushing? I do one every day prior to diving. I think a nice long flush is better as this optimises the amount of o2 across the face of the cells. I do the usual tests eg pos and neg etc. Then I just follow the handset instructions - easiest way then you don't make a mistake.

My understanding of the calibration is that you want to have pure O2 across the face of the cells at atmospheric pressure (1000mb is fine - if you have say a VR3 you can put the actual reading). If you are keeping the mouthpiece closed and then opening you are not doing a cal at atmospheric pressure. This could be why your getting a slight low reading in air. All a callibration does is that a cell does not know what partial pressure of o2 is across it - all it does is produce an electric charge (ie voltage) in response to the oxygen across it. By callibrating it you are telling the handsets at what voltage the cell is reading 100% (I use 98% on the menu) oxygen. From this the handset can then work-out the partial pressure from the voltage that is given off.

The readings during calibration are voltages not partial pressure. It is only once the unit has done its double bleep that you get a partial pressure.

So in summary - I just follow the instructions that the handset says everytime I switch the unit on - that way you don't make a mistake. Once the cal is over I do a pre-breathe check (often like to lower the pO2 to get an alarm) before the solenoid clicks in and raises the pO2 and then a continue to breathe ensure all 3 readings are stable around the 0.7 mark.

Hope this helps.