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Thread: Conductivity Probe Calibration Low

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    Conductivity Probe Calibration Low

    So as to be expected my conductivity probe was all over the place for the first couple weeks. When it became stable and I could "calibrate" it with tank water it only fluctuated 0.2-0.3ppt max, which is good for me. I then did a calibration with the 53,000 solution. I soaked the bag in my sump for 30 minutes. Rinsed my probe in RODI and used canned air briefly to blow it off. Did calibration in Advanced mode. Cut the corner off the solution bag and tried my best to make sure no air bubbles in probe (swish, gently tap probe). Clipped bag and probe into sump for 30 minutes to stabilize reading. Immediately after calibration my probe read around 32.5ppt while still in the calibration solution. This seems odd to me because if I just told it was in a 35ppt solution for calibration I would expect it to read 35ppt immediately after calibration in the same solution at the exact same temperature with nothing moving. After moving the probe to my tank water it reads 32ppt and has been very stable for a day. My tank is about 34ppt per my good refractometer which I checked in a 20c metrology lab and compared to my home environment with the same solution. I have not yet dead on verified the 2 apex probes I have in my sump so I am taking my decent calibrated digital thermometer and will have it put into a probe calibration well at 78F to get an accurate offset from the calibrated accuracy of +/- 1deg so I should be able to set my apex probes with a little less measurement uncertainty (this is probably overkill). Oh and my TC is default 2.2.

    So all that said, I am going to try again with a new bag soon. Any ideas on where the problem might be?

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    Try a probe "reset". Unplug the probe, run a calibration and then plug it back in (it sometimes helps if you reboot after this but is not required). Then try the same calibration procedure as before because you got everything right there. If it doesn't give you 35ppt in the packet, reboot and try again.

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

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    I'm in the process of trying that now. I'll reboot, why not... that's easy. Should I reboot after reset with probe still unplugged or after and plug it back in? Also I didn't document my reading during calibration which I will do from now on. I remember it was 70-71 dry (which I think is normal). What reading should I expect when it is in solution? Also is there any harm in a brief vinegar soak before rinse and dry? Seems like a good idea to remove any mineral deposits, but not sure if it will have other effects.

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    Quote Originally Posted by Diznaster View Post
    I'm in the process of trying that now. I'll reboot, why not... that's easy. Should I reboot after reset with probe still unplugged or after and plug it back in? Also I didn't document my reading during calibration which I will do from now on. I remember it was 70-71 dry (which I think is normal). What reading should I expect when it is in solution? Also is there any harm in a brief vinegar soak before rinse and dry? Seems like a good idea to remove any mineral deposits, but not sure if it will have other effects.
    Doesn't matter for the unplugged part. Makes zero difference either way.

    70 is normal for the dry step. Most are in the -20 to 100 range. For the wet step, expect something between 500 and 700.

    You can safely soak the probe in vinegar. Just make sure to give it a good rinse in RODI after and keep rinsing until the smell goes away.

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

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    So I just finished cal after a reset/reboot. I didn't do a vinegar soak my probe is almost new, but might be a good idea after a few months of use. After calibration and still in solution it read 29ppt. Frustrated, I changed TC% to 0.0 and it jumped to 34ppt which is darn close. Then I set it back to 2.2 and it is now at 33.4. This is all still in 53,000 solution.

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    I just did a quick re-cal with the same packet but set TC to 0.0 before calibration. It finished at 34.9 which I would expect. When I set TC back to 2.2 it dropped to 34.1. Cal1 was 534 wet and Cal2 was 529 wet (but didn't soak as long).

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    Quote Originally Posted by Diznaster View Post
    So I just finished cal after a reset/reboot. I didn't do a vinegar soak my probe is almost new, but might be a good idea after a few months of use. After calibration and still in solution it read 29ppt. Frustrated, I changed TC% to 0.0 and it jumped to 34ppt which is darn close. Then I set it back to 2.2 and it is now at 33.4. This is all still in 53,000 solution.
    That's got to be a bug or something I would create a support ticket and see if they can find a problem somewhere.

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

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    Last Hour has been 34.4ppt in tank water with no fluctuation TC at 2.2. I wouldn't dream of controlling anything with this probe besides a massive delta stopping something like an ATO and the other time fail safes should have kicked in before then. It would be cool if I could trust the new calibrated value. Being realistic, I could probably "calibrate" on tank water and clean often achieve this. I work in dimensional inspection and calculated uncertainty of calibrated equipment in practice is a big factor. I don't feel like spiting microns or microsieverts. The absolute value is not reliable here, the delta might be reliable. If that holds true it works for me.

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