# milwaukee sms122 setpoint question (again)



## gmaniac (Mar 12, 2004)

Hi All
I have read all the posts on this SMS 122 controller and I finally got mine in the mail today! I consider myself to be somewhat smart...but after calibrating it, I CAN'T figure out (from the inadequate directions) how to set a high point and a low point on the controller. I can turn the black knob in the center, and put the arrow on a pH value, but there are no buttons or instructions on setting a set point. Maybe it is something small that I am missing because I just don't see how to do it.

please help...really appreciate it

thanks in advance!!

GM


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## Splash (Feb 18, 2004)

gmaniac,

I'm not sure from your post whether you first calibrated your controller. As a minimum, you first need to adjust the "offset" calibration trimmer on the front of the controller using a pH 7 calibration solution. You should have received a little screwdriver with the controller with which to make this adjustment.

Once your offset is adjusted to pH 7.0, you really ought to adjust the "slope" calibration trimmer on the back of the controller using a pH 4.0 calibration solution. Milwaukee Instruments might have included a note with your controller that says you can skip this step, but see the hyperlink below for why you should do it anyway. (Basically, it allows you to better track the drift and deterioration of the probe over time.)

Once your controller is calibrated, you set a single "set point" with the black knob on the front. When the pH rises about 0.05 pH above that set point, the controller opens the solenoid on your CO2 regulator and lets CO2 into your diffuser. When the pH then drops about 0.05 pH below your set point, the solenoid closes, and CO2 stops flowing. The set point is the "optimal" pH you want for your tank.

Two things you ought to know ahead of time. (1) There is a fair bit of "play" in the black knob, so don't assume you can set the set point by lining the knob marker with the surrounding numerals. That gets you in the right ballpark, but you should monitor the digital meter carefully for a few hours as you tweak the knob back and forth a bit to get the desired set point. (2) The set point response is not exact. No matter how much you fiddle with the black knob, your digital pH reading will wander over a range of about 0.1 pH. (Example: Mine wanders between 6.8 and 6.9.)

Here is a link that has good information on how to calibrate a pH meter and do maintenance on a pH probe: http://www.digital-analysis.com/Tarticles.htm.

Cheers!
splash




gmaniac said:


> Hi All
> I have read all the posts on this SMS 122 controller and I finally got mine in the mail today! I consider myself to be somewhat smart...but after calibrating it, I CAN'T figure out (from the inadequate directions) how to set a high point and a low point on the controller. I can turn the black knob in the center, and put the arrow on a pH value, but there are no buttons or instructions on setting a set point. Maybe it is something small that I am missing because I just don't see how to do it.
> 
> please help...really appreciate it
> ...


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## gmaniac (Mar 12, 2004)

Thanks a ton, Splash....very helpful info!!!

I understand the setpoint now..that really helps...I got the impression from reading the posts that there was the ability to set a high and low setpoint for the SMS122. I have calibrated at 7 and will obtain a 4 standard solution to calibrate at the low end 

This is the scenario as I understand it.... for the SMS 122:

There is only one setpoint (not a separate high and low one) and if I set the setpoint (black knob ) to 6.8, and my tank is at 7.3..... the alarm light on the unit will blink and CO2 will flow until the 6.8 pH is reached, then the alarm shuts off and the CO2 stops flowing?

Is that an accurate assessment? It is basically reiterating what you have said

thanks again

GM


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## Splash (Feb 18, 2004)

Yep; you got it. 



gmaniac said:


> Thanks a ton, Splash....very helpful info!!!
> 
> I understand the setpoint now..that really helps...I got the impression from reading the posts that there was the ability to set a high and low setpoint for the SMS122. I have calibrated at 7 and will obtain a 4 standard solution to calibrate at the low end
> 
> ...


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## ricoishere (Jan 26, 2009)

This is an old string, But I'm going through the same issues. The instructions are less than adequate.


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