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Thread: HUD and Controller calibration

  1. #1

    HUD and Controller calibration

    Hi Guys,

    Can I please ask your input on the implications of the following?

    I am having issues to make the calibration of the JJ controller match the calibration of the HUD. The controller seems to be reading a bit higher than the HUD. In theory the HUD should be showing 1 orange at 1.0 (0.95-1.05) but when compared to the controller the controller seems to be reading between 1.04-1.10. This seems to be less of a noticeable problem at 0.7 as I do get 3 red dots or 1.3 as I do get 3 green ones. So the variance seems to be small and only noticeable around 1.0

    I’ve tried several times and the outcome seems pretty consistent.
    I think I know why this is happening and I think I know how to correct it but I am not sure of the implications of it thus, I would like to hear your input.

    • a) Page 36 of the manual states that “the calibration gas must be set to 100% oxygen”
    • b) However, the HUD assumes that “The actual value it uses for calibration is .98.” Shearwater HUD ***8211; Shearwater Research
    • c) The predator manual states the following: “The system defaults to a calibration gas of 98% oxygen. This is to compensate for the difficulty in completely filling the loop with 100% oxygen and also to allow for water vapour.”



    This would explain the difference in readings. In fact, if I modify the settings in the controller to calibrate to 0.98 both the HUD and the controller match a lot more closely.

    So, should I be concerned or not?

    For starters, I am not 100% clear if the 0.02% difference will make a significant difference and I’m making a storm on a tea cup

    Thanks

    D

  2. #2
    Banned Dave Sutton's Avatar
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    Getting the cal right is a good thing, so by all means try your best.

    But.....

    Storm in a Teapot is about right. 0.02 is noise. 0.2 is a small signal. We are talking about measuring with a micrometer what we ought to be measuring with the widths of our toes. In the old days we had analog needles on a jeweled meter movement and could read down to a resolution of about 0.4 so... With more precise instruments comes the belief that this resolution means something when in fact it's not really useful at all.

    Dave

    .

  3. #3
    If you want a more precise calibration use a pressure pot like the one by narked at 90 that allows you to plug the cells into the rebreather. This isolates the cells and assures they are flushed with 100%. It is also the only way to calibrate the shearwater HUD at altitude. Because you can pressurize the pot to 1 ata.


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  4. #4
    Thanks guys,

    So, if the variance is not that relevant and for the sake of having the two pieces of equipment showing the same outcome, should I set the predator to 0.98 even if I'm calibrating with 100%?

    It will mean though that I'd be running a slightly hotter mix and that is what I'm getting worried about.

    D

  5. #5
    Hello,

    As I wrote the manual, I'll try to explain why I wrote the part with the 100% oxygen:

    As long as you are not using the "Auto" altitude setting, the .98% setting is working fine. This will also match the HUD calibration and the controller and HUD will show the same values (small differences are always possible).

    When the altitude setting is set to "Auto" the controller is taking the ambient pressure into account. With 98% oxygen and when you are not at sea level, the final calibration will end up with a value below .98. In this case you will always have different values on the HUD and controller.

    I used the following settings:

    Diving at sea level:

    Altitude: "Sealvl"
    Oxygen: 98 %

    Diving above sea level:

    Altitude: "Auto"
    Oxygen: 100 %

    DIN

  6. #6
    Quote Originally Posted by Dinspiration View Post
    I used the following settings:

    Diving at sea level:

    Altitude: "Sealvl"
    Oxygen: 98 %

    Diving above sea level:

    Altitude: "Auto"
    Oxygen: 100 %

    DIN
    On my Level I course I was told to calibrate with the controller set to 100% - the altitude wasn't mentioned but we were diving in the sea.

  7. #7
    Quote Originally Posted by Dinspiration View Post
    Hello,

    As I wrote the manual, I'll try to explain why I wrote the part with the 100% oxygen:

    As long as you are not using the "Auto" altitude setting, the .98% setting is working fine. This will also match the HUD calibration and the controller and HUD will show the same values (small differences are always possible).

    When the altitude setting is set to "Auto" the controller is taking the ambient pressure into account. With 98% oxygen and when you are not at sea level, the final calibration will end up with a value below .98. In this case you will always have different values on the HUD and controller.

    I used the following settings:

    Diving at sea level:

    Altitude: "Sealvl"
    Oxygen: 98 %

    Diving above sea level:

    Altitude: "Auto"
    Oxygen: 100 %

    DIN
    Hi,

    Thanks for that.

    I'll modify my settings accordingly. I realise that in normal operation this is not an issue, however, this is my first ccr and I'm still doing drill-only dives at shallow depth. It has been a bit annoying to have a 0.5ish difference between one and the other

    That translates in one red blink with the controller at 1.0, 1 Orange blink with 1.08 and so on. This makes me second guess if I'm trying to fly the unit with only the HUD or the only controller. As I said before with a set point of 0.7 it does blink 3 times red and with 1.3 it does blink 3 times on green. Therefore I know it's around the edges.

    Anyway, thank you so much

    D

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