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Thread: Best practice in calibrating the 2016 salinity probe

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    Best practice in calibrating the 2016 salinity probe

    I'd like to know the best way to calibrate the probe. I've calibrated by bring the solution up to temp, shaking out and calibrating but it's reading high (35.4) when the water is only 1.023. I watched the BRS video but didn't see anything about the temperature probe and temperature compensation when I was doing the automatic calibration. Is this still applicable with the 2016 model?

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    Yes you can use temp compensation by selecting the Advanced Tab and set the temp compensation save that to the Apex and then calibrate the salinity probe.
    Jon
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    The "best" way to do it is actually to adjust your tank temperature to 77 degrees or use a separate vessel heated to 77 degrees with the temp probe placed in it. Float the packet in that water for minimum 15 minutes (30 better) and calibrate there with temp compensation enabled. This is kinda a PITA since it requires you to change a bunch of code and can piss of livestock or makes your heaters and chillers act wrong if you use a separate vessel. so the next best thing (and the way most do it) is to float the calibration packet in your sump for 30 minutes and calibrate in sump if possible (you would need a clip) and out of sump if not with temp compensation enabled.


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    Quote Originally Posted by zombie View Post
    The "best" way to do it is actually to place your temp probe in a cup of tap water that is as close as possible to 20C as you can get. Float the packet in that water for minimum 15 minutes and calibrate there with temp compensation enables. This is kinda a PITA since it requires a bunch of code to keep heaters and chillers from going wack so the next best thing (and the way most do it) is to float the calibration packet in your sump for 30 minutes and calibrate in sump if possible (you would need a clip) and out of sump if not with temp compensation enabled.


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    Ok, so float the packet in the sump for 30 minutes and calibrate inside packet while still in sump. I will not need to enable temperature compensation for this. If I cannot calibrate in sump i will need to enable temperature compensation and leave temperature probe in sump?

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    I would enable temp compensation either way (its a bit mire accurate with it on). You just want to be pretty quick about it once you take it out of the sump because it will cool.

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    FYI, I made a mistake above. I forgot neptune use 25C (77F) calibration standard so that is the temp you want to get as close as possible to. My original post has been updated.

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    I made the mistake of not heating to desired Temp or placing in the sump firstly and now my salinity reading is very low which is not really when testing with a refractometer im talking low 20's on dashboard! what should i do?

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    Quote Originally Posted by Gaz Mortlock View Post
    I made the mistake of not heating to desired Temp or placing in the sump firstly and now my salinity reading is very low which is not really when testing with a refractometer im talking low 20's on dashboard! what should i do?
    Recalibrate at the proper temp. If you don't have more packets, get some on order (I suggest getting quite a few as this needs to be done monthly in an ideal world and no less than quarterly) and ignore the readings until it reads correctly.

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    Quote Originally Posted by zombie View Post
    Recalibrate at the proper temp. If you don't have more packets, get some on order (I suggest getting quite a few as this needs to be done monthly in an ideal world and no less than quarterly) and ignore the readings until it reads correctly.

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    I get that now. Would you mind elaborating on your previous comment that using temperature compensation would require a bunch of code to get heaters to work right? It confused me a bit since you then suggested using it.

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    That was not due to enabling temp compensation. That code was if you calibrate at the ideal temp (25C) to avoid the unknown temperature buffering effects of the calibration solution.

    Simply heating the packet in your sump is adequate enough (should result in less than 0.1ppt error) as long as your temperature does not exceed 79 degrees during calibration. Outside of that the temperature buffering effect of the calibration vs the temp compensation algorithm can cause a noticeable error.

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    Quote Originally Posted by zombie View Post
    That was not due to enabling temp compensation. That code was if you calibrate at the ideal temp (25C) to avoid the unknown temperature buffering effects of the calibration solution.

    Simply heating the packet in your sump is adequate enough (should result in less than 0.1ppt error) as long as your temperature does not exceed 79 degrees during calibration. Outside of that the temperature buffering effect of the calibration vs the temp compensation algorithm can cause a noticeable error.

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    So I calibrated just as you've stated. My Vee Gee refractometer is reading 1.024 and the probe is fluctuating between 32.7 and 34.1. Can you take a peak at my graph to see if this appears right? Should I try lowering temperature compensation? I calibrated with it at 2.2. Screen Shot 2017-06-21 at 6.06.08 PM.jpg

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    Try 1.1 for the temp compensation. I think it might be a bug in the firmware making it compensate based on F instead of C like it's supposed to. Someone else had the same problem recently.

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    Quote Originally Posted by zombie View Post
    Try 1.1 for the temp compensation. I think it might be a bug in the firmware making it compensate based on F instead of C like it's supposed to. Someone else had the same problem recently.

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    I'll try that. Do I have to recalibrate?

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    If your temp was within a degree of 77F when you calibrated the error should be small enough recalibration won't be necessary. Any more than that and it wouldn't hurt.

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    Quote Originally Posted by zombie View Post
    If your temp was within a degree of 77F when you calibrated the error should be small enough recalibration won't be necessary. Any more than that and it wouldn't hurt.

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    Changing it to 1.1 caused the salinity to read higher than with the 2.2. I'll stick to the original calibration and recalibrate in a few weeks.

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    Play around with the compensation value in the meantime until you get a variance of 0.2 or 0.3 as temp fluctuates. That way you know it will be right when you calibrate next.

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    I just posted this in another thread, but its also something to keep in mind while you are calibrating:

    I thought this would be a good example to show something. I don't have anything electrical (pumps, powerheads, etc) around my probes because it causes interference, but I do have my wires neatly zip tied together as they make their way along the back of my sump. Last night I had to add a new wire to the mix and simply cut all the zip ties so the existing wires are hanging loosely. See the pic of my graph and what a difference this alone makes. For accurate readings it really is important to keep the probes and wires isolated.

    S.PNG

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    Quote Originally Posted by Scott.h View Post
    I just posted this in another thread, but its also something to keep in mind while you are calibrating:

    I thought this would be a good example to show something. I don't have anything electrical (pumps, powerheads, etc) around my probes because it causes interference, but I do have my wires neatly zip tied together as they make their way along the back of my sump. Last night I had to add a new wire to the mix and simply cut all the zip ties so the existing wires are hanging loosely. See the pic of my graph and what a difference this alone makes. For accurate readings it really is important to keep the probes and wires isolated.

    S.PNG
    I recalibrated again and this time I'm ranging between 32.4-33.2. Again, my actual PPT is approximately 32.5 as tested by my refractometer. I guess this isn't too bad. I don't have my probe wires zip tied together but they are in the same chamber as my return pump (red dragon 150 DC) and heaters. I may trying moving the salinity probe to another chamber. I'm not too worried about it since I'm going to rely on my refractometer and not my probe but it would be nice to get a solid reading.

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    With that range it's just as likely that the refractometer (or your perception of where the half mark is) is off just a tad. Every refractometer I have ever used is nearly impossible to spot a difference between a reading of 35 vs 34.5 and 35.5

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    Quote Originally Posted by zombie View Post
    With that range it's just as likely that the refractometer (or your perception of where the half mark is) is off just a tad. Every refractometer I have ever used is nearly impossible to spot a difference between a reading of 35 vs 34.5 and 35.5

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    Yeah, I suppose you are correct. I've been trying to have the probe deviate less than .3-.4 but cannot manage that. I'm going to just let it be now and only pay attention when it drops or rises too much.

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    One thing that just crossed my mind...do you have your temp probe in the PM2? Unless they changed the firmware, temp compensation for the probe only works when the temp probe is in the PM2 that could explain why it's still deviating even though you changed the compensation value.

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    Quote Originally Posted by zombie View Post
    One thing that just crossed my mind...do you have your temp probe in the PM2? Unless they changed the firmware, temp compensation for the probe only works when the temp probe is in the PM2 that could explain why it's still deviating even though you changed the compensation value.

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    I only have a temperature probe plugged into a 2016 head unit. Should I disable? Do I need to recalibrate? I calibrated at precisely 73.3F in sump.

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    I would either get a second temp probe (more relaible since heaters still work if PM2 gets disconnected) or move it to the PM2. If you move it make sure your heaters and whatnot get their code adjusted so they use the different port.

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    But make sure you get the temp compensation dialed in before calibrating. Start at 2.2 if the relationship between temp and cond is proportional then bump it up 0.1, If the relationship is inverse bump it down 0.1 until it stays relatively constant.

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    Quote Originally Posted by zombie View Post
    But make sure you get the temp compensation dialed in before calibrating. Start at 2.2 if the relationship between temp and cond is proportional then bump it up 0.1, If the relationship is inverse bump it down 0.1 until it stays relatively constant.

    You might be an engineer if...You have no life and can prove it mathematically.
    Are you saying I need to buy a PM2? I thought the whole purpose of the new model was the ability to measure salinity with the head unit.

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