Calibrating a refractometer

Discussion in 'Test Kits, Controllers, Reactors and Dosers' started by Nico Kortenbout, 3 Dec 2011.

  1. Nico Kortenbout

    Nico Kortenbout

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    Hi all,

    I have used RO/DI water to calibrate my refractometer. My understanding is that RO/DI water should have a SG of 1.

    I thought that there might be an issue with the calibration when it measured NSW to have a SG of 1.023, so I checked against RO/DI and it was 1.002. I set it to read 1.000 for RO/DI and it now measures NSW at 1.026 and my tank water at 1.025.

    I would just like to confirm that what I have done is correct.... Thanks a bunch.

    Nico
     
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  3. Nemos Janitor

    Nemos Janitor

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    There are different types of refractometers. I am going to assume yours is a ATC refractometer.

    If you look in the viewer you should see something like 20/20 or 20c. this is the calibration temperature. It is important to calibrate the refractometer at that temperature. I am not talking about the water temperature. I am referring to the temperature of the instrument.

    Your sg is then referenced to the calibration temp. So in your case 1,025 at 20 c.
    Once calibrated at 20c the ATC will compensate for the temp of the instrument up to a temp of 30c in most cases. but even if the instrument is at say 28c the sg is still 1.025 at 20c.
     
    Last edited: 3 Dec 2011
  4. OP
    Nico Kortenbout

    Nico Kortenbout

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    Ah, cool thanks, yes it has a 20c calibration temp. I will use the aircon to get a room to 20c with the instrument and then recalibrate.
     
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    Nico Kortenbout

    Nico Kortenbout

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    Just to check then... should i still use RO/DI for the calibration and set SG=1 or use NSW and set at SG=1.025?
     
  6. Nemos Janitor

    Nemos Janitor

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    Use DI/RO water. The sg of NSW can change from day to day.

    If you want to use a reference solution you must find one that is referenced at the refractometers calibration temperature (20c) most that i know of are referenced at 25c.
     
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    Nico Kortenbout

    Nico Kortenbout

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