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I believe you're supposed to use the PH calibration fluid, 7.01 (NOT 4.01), and adjust the screw on your (sms122?) to 7.0 (not 7.1, b/c something about atmosphere or something fancy)
 

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The instructions on the SMS122 say *not* to use the 4.01 fluid if doing freshwater tanks, only the 7.01....search around, seems to be backed
 

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for reasons why *not* to use the 4.01 fluid to calibrate, see this thread:
http://www.plantedtank.net/forums/e...libration-solution.html?highlight=sms122+7.01

Also, yes, the instructions that come with the SMS122 *DO* say to use both the 4.01 and the 7.01...HOWEVER, there is also a 'new' (apparently new, responding to criticism as found in the above thread) flyer saying not to use 4.01 to calibrate for fresh water setups.

To quote the flyer exactly: "Please Note: Because the SMS122 is used primarily in an aquarium environment we strongly recommend that your unit be calibrated at the ph7.0 position only. We have included just a starter pack of ph calibration solution 7.01. If your application needs require calibration solution for the Acid or Alkali ends of the ph scale please let us know and we will provide the proper calibration solution."
 

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I have two of the Milwaukee SMS 122 controllers. I calibrated mine with only the 7.01 buffer solution and they work fine. There's only a 0.2 pH swing from it's start point until it's endpoind. My suggestion to you is to calibrate them just like Nbot has been telling you, Orlando.
 

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You calibrate your SMS122 to 7.0 (using the 7.01 fluid and the adjustment screw on the *FRONT* of the SMS122). If it is calibrated like this, then, when you stick the SMS122 probe into your tank, it will tell you what the tank's ph is. Theoretically the controller and the AP kit should say the same thing, but there might be some difference, I assume for the "slope" of things, or one tool being more accurate than the other.
 

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Ditto on just using the 7.01 buffer to calibrate. That is the standard practice and don't bother with the 4.01 as it might throw off the calibration. Also, I often get a range when comparing a SMS probe to a handheld Hanna pHep 4. Maybe .2 difference or so. I don't know this, but suspect the age of the probe and the "alchemy" of testing pH explain the difference. I suppose it its that close, who cares.

PS, remember to replace the SMS ( or any probe) about once a year as they give wacky readings once their lifespan is coming to a close.
 

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I have in the past compared an AP test to my Hanna pHep4 to my SMS122. Both digitals were recently calibrated. All were within (well eye test is subjective) about 3/10 of a unit.

But to answer your question, I would think if you tested your meter to a different "known" buffer, it should read fairly close. One thing that is said to throw off readings are ballasts from lights being on. But my light on or off doesn't seem to affect it. Nonetheless, I rarely get the exact same reading from two different digital meters. But they are usually fairly close.
 

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ok, definitely do what the manufacturer recommends. they obviously know best and i completely agree with that recommendation. BUT... if you adjust using only one calibration solution, do you use another one or two 'known' solutions to determine it's working accurately? basically, i should be able to use a pH4 solution and it should read pH4, right? if you want to evaluate the accuracy of measurement, you can measure either a) against a sufficiently more accurate test method or device, or b) the known 'truth' of the thing you are measuring. specifically, using another test kit or pH measuring device as 'truth' is only valid if it has significantly better accuracy than the monitor under test.
-snafu
"A man with a watch knows what time it is. A man with two watches is never sure."
I know what your are saying, but as near as I can tell, it's very close. I'm not having any problems with them. I don't know why Milwaukee says to only use a 7.01 buffer solution for use in our aquariums. A two or three point calibration would be better, it seems, but I just follow the directions. I have some of all three pH buffer solutions. I might try them the next time that I calibrate my probes to 7.0 just to see what they read.

I meant to add this. I remember reading about several people that used the slope adjustment (4.01) and really messed the unit up. I've also read about a few people that have used the 7.01 and the 4.01 buffer solutions and didn't have any problems. I'm going to continue with what I am doing now. As the old expression says, "If it isn't broke, don't fix it."
 

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Snafu...I'm with you, it doesn't make any sense why you calibrate only the 7 and not the 4, no sense at all....something about a 'slope' but I won't pretend to understand, just following the directions on this one:)
 

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Discussion Starter · #15 ·
The monitor I own is from Florida drift wood. It measures 7.00, instead of 7.0
The directions it came with are translated in the worst English. I still don't know what kind of controller it is. I got a sweet deal on it because the guy wants me to be a wholesale distributor. So he gives me these deals. check out the site and look at the controller, any idea what kind it is?
 

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look at the response of the electrode (aka probe) in the following reference (graph in the lower right).

http://www.4oakton.com/TechTips/TT_ph.pdf

you'll notice that the pH response is fairly linear. also note that the electrode outputs 0mV at a pH7 regardless of temperature. sometimes when you are measuring a pH7 solution, the output is not 0mV, so you have to provide an offset (or shift the line down or up). this is known as the 'offset' adjustment. you 'offset' the curve up or down.

the electrode will generally output a constant mV per unit pH at a constant temperature (or in other words - a straight line as shown in the graph). sometimes the slope isn't correct and requires adjustment (possible a higher slope or lower slope). in order to do this, you need to use a solution other than 7, like pH4 or pH10 as an example. this is known as the slope adjustment. there is probably a recommended procedure for calibrating the monitor. for example, it will tell you to adjust the offset first before the slope, because if you did the reverse you'd never get it right. this might be the reason people aren't able to get the correct calibration.

to reiterate, it really depends on how the electronics are designed. so, always follow the recommended calibration procedure from the manufacturer.

-snafu
I have some comments.

1) I agree with what you are saying, but you are using directions from Oakton. I had an Oakton pHTestr 20 up until a year ago. You can do two or three point calibrations with it. The pH testers that we use in our biotechnology have two or three point calibrations as well. We are talking about the Milwaukee unit. Your concern should be directed to the Milwaukee Instruments company. My two units work fine just the way the are. There's only a pH swing of 0.2 like I mentioned earlier. Maybe Milwaukee adjusts the slope prior to shipment so that we only need to calibrate it with a 7.01 buffer solution for our aquariums. I don't know if they do or not, it's just a guess. I really don't know why Milwaukee only advises to do the one point calibration. I have drop checkers made with a known KH solution in those same tanks and they are in agreement with the pH level that the Milwaukee controller shows.:icon_smil

2) Orlando, who started the thread, doesn't even have a Milwaukee controller. It's an unknown brand pH monitor.:icon_lol:

3) How did the Milwaukee controller get tangled up in this?:hihi:
 

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it's true the said reference is from oaktron. the graph is a general one for a typical pH electrode. it has nothing to do with any particular type of monitor or controller. if you pull up a response curve from another electrode/probe vendor you will see a similar profile, roughly 59.2mV per unit pH. i was merely explaining what a probe typically produces and what is meant by offset and slope.

lastly, if it's still not clear... what i have said and will reiterate yet again is that each manufacturer will have a different electronic design and therefore will have different calibration procedures. you should follow the calibration procedures provided by the manufacturer.
-snafu
Snafu,

I have already told you that I agree with what you are saying about pH controller calibration several times already! I have been using electronic pH monitors and testers for over 30 years now. I certainly know how to calibrate them and how to use them. You've driven your point into the ground.

I've also told you several times that I don't have any problems with my controllers and their calibration settings.

Why in the world do you keep dragging this around? The person that started this thread, orlando, doesn't even have a Milwaukee controller. Address your responses to orlando's question and not me.

I'm sure that I don't like this comment, "lastly, if it's still not clear... " I can tell you what's clear but I won't!

This should be the end of these comments directed at me in this thread!!
 
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