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Thread: Ph probes do not match after several calibrations

  1. #1
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    Ph probes do not match after several calibrations

    I bought an additional Apex ph probe, so now I have two. I have calibrated them both several times with 7.01 and 10.01 calibration fluid. They sit within an inch of each other but when I put them in the tank, they give readings that are over 25 points off from each other. When I stick each of them separately in the 7.01 and 10.01 fluid, they are dead on accurate. When I put them back in the tank, 25 point difference- like one reads 8.25 and the other 7.99.

    Anyone have this issue? Any way to solve this? Makes me question the whole accuracy of apex probes all together.


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  2. #2
    Frequent Contributor zombie's Avatar
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    If you remove them from the tank and place them in a cup of tank water do they read the same value?

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by zombie View Post
    If you remove them from the tank and place them in a cup of tank water do they read the same value?

    You might be an engineer if...You have no life and can prove it mathematically.
    No, just tried it. One reads 8.33 and the other 8.05.


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    Frequent Contributor zombie's Avatar
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    If you switch ports and recalibrate see if the higher reading follows the probe or the port. Make sure to let each settle for no less than 5 minutes in each solution. If it follows the probe, then one of the two may have developed a non-linearity in the output voltage. If it follows the port, contact support.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by zombie View Post
    If you switch ports and recalibrate see if the higher reading follows the probe or the port. Make sure to let each settle for no less than 5 minutes in each solution. If it follows the probe, then one of the two may have developed a non-linearity in the output voltage. If it follows the port, contact support.

    You might be an engineer if...You have no life and can prove it mathematically.
    Do I need to recalibrate before switching to see if it follows the probe? This would be the 5th time to calibrate in the last 48 hours each time for longer than 5 minutes? How do I know which one is nonlinear if it follow the probe?


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    Frequent Contributor zombie's Avatar
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    Quote Originally Posted by mginani View Post
    Do I need to recalibrate before switching to see if it follows the probe? This would be the 5th time to calibrate in the last 48 hours each time for longer than 5 minutes? How do I know which one is nonlinear if it follow the probe?


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    It wouldn't hurt to do so. As long as you clean the solution off of the probe between switching between solutions, you can use the same packet for all 4 calibrations.

    You won't know which is non linear without a reference solution between 7 and 10. You will only know that one of them is.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by zombie View Post
    It wouldn't hurt to do so. As long as you clean the solution off of the probe between switching between solutions, you can use the same packet for all 4 calibrations.

    You won't know which is non linear without a reference solution between 7 and 10. You will only know that one of them is.

    You might be an engineer if...You have no life and can prove it mathematically.
    I guess I could just test my ph by another method and then see if one is more accurate.


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  8. #8
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    I switch probes and the ph followed the probes. I checked ph with my seneye and oddly enough, the older probe is accurate and the new one is not. I guess I will get in touch with Neptune.


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