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  1. #91
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    https://drive.google.com/file/d/1GZk...w?usp=drivesdk

    Not sure if the link wil work but this was one of the docs referencing in water linearity checks

  2. #92
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    Quote Originally Posted by JonG View Post
    I agree that 3% seems like a very tight tolerance against a woolly reference point, and I have read that other's accept 5% and in 1 case 10% depending on the dive and with a reduced target set point.

    I thought the red cell was pretty much what cell linearity checks were driving us to seek to avoid, where the drop could lead to an erroneous handset reading, with enough margin to be threatening.

    Have u read the CCRX posting?
    I have no idea what people are calling things - but lets be clear the red line is straight - not a curve ... it is linear. Linearity checks are to check that the first order chemical reaction is in the zone that can be approximated by a straight line. The red line is a failed calibration.

    If I get a reading that is more than 5% off (~2.5mV in O2 expected ~50mV with correspond air mV of 10.x) I reject the calibration and find out why the cell is reading outside of its expected. Its usually a slow cell or incomplete flush during calibration (you could do a manual O2 flush or let unit stabilise at SP of 0.7 (rather than turning unit on and calibrating immediately) and then calibrate again) - you could also expose cells to air again and check their mV readings - these will vary by 0.1-0.2 mV. (0.2 is ~4% btw which again shows why labouring over such "false" accuracy is completely meaningless)

    Just go diving ... you are tying yourself in knots for no reason- what does it matter if your actual PO2 s at 1.3 instead of measured 1.2? If you really consider it to be important (are doing dives where it might matter or just splashing for 60-90mins) just drop the PO2 to 1.0 on the bottom...

  3. #93
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    I'm fine with it Graham it's not keeping me dry!

    It does seem like there is a lot of confusion generally if you read the threads, FB page posts and the draft paper prepared by a us instructor.

    On CCRX 80 votes in a poll suggested that the voters were completing in water linearity and current limiting checks.

    I was interested in the seeming difference between UK and US and have learnt some stuff.

    If anyone else does, happy days.

  4. #94
    Coastal Member dwhitlow's Avatar
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    Quote Originally Posted by JonG View Post
    I'm fine with it Graham it's not keeping me dry!

    It does seem like there is a lot of confusion generally if you read the threads, FB page posts and the draft paper prepared by a us instructor.

    On CCRX 80 votes in a poll suggested that the voters were completing in water linearity and current limiting checks.

    I was interested in the seeming difference between UK and US and have learnt some stuff.

    If anyone else does, happy days.
    I went diving today. My rebreather seemed happy (I got a bag of scallops too) but my 4th cell was behaving oddly.

    I suspect cell #4 will soon be in the discarded and cell #1 (oldest) is due for relocation and replacement.

    I'll not be reading posts by people I have reason to trust and instead I shall back off to first principles and decide what to do.

    This seems simpler, more relevant, and a whole lot safer than asking the (largely) uninformed masses of the Internet to determine my actions.

  5. #95
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    Quote Originally Posted by dwhitlow View Post
    I'll not be reading posts by people I have reason to trust and instead I shall back off to first principles and decide what to do.

    This seems simpler, more relevant, and a whole lot safer than asking the (largely) uninformed masses of the Internet to determine my actions.
    That seems a bit harsh. he's only trying to understand how things work; not telling everybody who replies that they're wrong.

  6. #96
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    Quote Originally Posted by JonG View Post
    I was interested in the seeming difference between UK and US and have learnt some stuff.

    If anyone else does, happy days.
    American bail out calculations;

    side mount a pair of 104 cubic foot tanks which are actually 102 cubic foot when filled to 3200psi but you're actually going to filled them to 3580psi, your rmv is x cubic foot and you are making a 100 foot dive, the surface pressues is y inches of mercury
    how many gallons of wind will you have left after bailing out if you are 500ft away from the entrance and swim at 1.2 miles per hour?


    And you REALLY want to pay strict attention to the way they do maths...
    For the love of god why

    https://images.app.goo.gl/2nEeeNZUT9m3fvTs8



 
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