# PH Controller Calibration



## zuker (Jan 3, 2005)

For those that have decided to use the SMS 122 PH Controller by Milwaukee Instruments, it is important that the meter is calibrated correctly. I recently spoke to a rep from the company who offered the following calibration proceedure. He stressed the importance of this due to the fact that the dial on the front of the meter is NOT a precision dial.

Prior to beginning, ensure that your meter has been properly calibrated by emersing the probe in the appropriate solution. In this case, use of the 7.01 PH solution is appropriate. Once the probe is calibrated, follow the poceedure below:

-Begin by turning the dial, on the front of the meter, to the lowest setting.
-Make sure the instrument is on.
-Place the PH probe in a glass of tap water and allow reading to stabilize.
-Slowly start adding lemon juice, one drop at a time, stirring after each drop. This will make the water acidic and PH will start to drop.
-After each drop is added, allow the PH reading to stabilize.
-Continue adding lemon juice until the PH is where you want it. This is the PH that you want the CO2 to shut off at. For example, when your lights and CO2 come on in the morning, and PH starts to drop with the addition of the CO2, the PH Controller will turn the valve off once the set point is reached. In a balanced system, however, the CO2 will most likely never shut off. This is because you have achieved equlibrium in the absorption rate of CO2 by the plants and PH is remaining fairly stable. This is where the SMS 122 really shines...for example, if your solenoid valve should be stuck open and too much CO2 is being injected into the tank, the SMS 122 will override the valve and shut it off completly, thus, preventing a CO2 overdose.
-Finally, move the (black) dial on the front of the meter until the red alarm light activates.

Your meter is now calibrated and ready for use. I hope this has been useful to those that are using the SMS 122.


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## joshjv (Oct 6, 2004)

Thanks for that info!
I recently bought a used SMS122 controller... I used calibration fluids, but with either the 7.0 or 4.0, I see no change in the reading, would that mean my probe is bad??

Thanks!


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## zuker (Jan 3, 2005)

Ya, that could indeed indicate you have a bad probe. I'm not sure what the life of the probes are, but I have had mine up and running for just under four years. What you might try is using a probe cleaining solution; I have had good results with it and from what I'm told, it extends the life of the probe. What I usually do is gently scrub the tip with a soft toothbrush then put it in the cleaning solution for a couple of minutes. Here is the part number from Milwaukee:

MA9016 Cleaning solution in 220ml bottle

And the link to the website:

http://www.milwaukeetesters.com/

Before you throw away the probe, I would try to clean it. Then again, if you do everything above and it still doesn't work, at least you will have everything you need to clean and maintain the new probe. Let me know how it works out.


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## rcalzadilla (Aug 27, 2007)

zuker:
How often do you calibrate yout controller?
Do you know where the best price is at?
tks


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## zuker (Jan 3, 2005)

Regarding calibration, I will usually compare the results of a PH test to what the meter (probe) is reading. If the two differ significantly, then I will calibrate the probe. Usually however, the probe stays calibrated for awhile. I usually clean and calibrate twice a year. Although, this could vary, depending on what my crosscheck testing indicates.

Pertaining to cleaning solution and calibration fluid, I get my supplies from a local hydroponics store where I live. I really haven't shopped online for these items.


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