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Thread: 2 Ph probes Different Readings

  1. #1
    Regular Vistor
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    2 Ph probes Different Readings

    I have 2 Ph probes,both purchased,calibrated and installed at the same time(one is a lab grade and the other is standard grade).
    Each reading is consistently off by approximately .3 ,but do follow in sync.Its kind of a guessing game which one is accurate.
    Both are plugged into (classic)base unit ph,ph/orp.
    Is there a way to adjust one or the other to have same reading?
    I've had several probes over the years and have never been able to get 2 probes to read the same.(even directly after calibration)
    I've contacted Neptune in the past about this issue but it was never resolved.

  2. #2
    Frequent Contributor zombie's Avatar
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    Sometimes probes can have what is known as non-linearity error in the measurement. If one probe has high error and the other doesn't or one has concave error while the other is convex, the readings can be different despite both reading exactly 7.01 and 10.01 in calibration solution. To rule out calibration error, check both probes in the same packet to see if there are any differences in the 10.01 or 7.01 solutions. If there are, repeated calibrations usually will fix any deviation.

    Sent from my SM-G965U using Tapatalk

  3. #3
    Regular Vistor
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    Thanks for the reply,
    I checked each probe in same calibration fluid and are only slightly off(7/10).Re calibrated again.
    re checked it again in the same fluid,and they are reading the same.
    Then returned probes to display tank and again off by >.3
    I guess the probe curves are very different.

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