pH calibration 4.00 - 7.00 is FUBAR

Lifeguard™ - Reports key tank parameters
Edward
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pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sat Sep 20, 2014 7:04 am

I just tried to calibrate the pH probe using new Milwaukee 4.01 & 7.01 buffer solutions. The process apparently thinks the second one is pH 10. I repeated the calibration a second time. Same result. I also have a Milwaukee SMS120 pH meter. It confirms the buffers are ~4.0 and ~7.0. (Yes, I know. The calibration procedure should presume the second buffer is pH 7.00 regardless. That's ll the more reason to be concerned the Lifeguard has something seriously wrong.)

At this point, the Lifeguard pH meter is unusable. I'll try cycling the power, repeating the calibration.

Edward
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sat Sep 20, 2014 9:20 am

The device apparently thinks the pH 4-7 and pH 7-10 calibration buttons are both for pH 7-10 calibrations. At least for the unit I've got, this seems to be the case. Anybody else able to say they've successfully calibrated a Lifeguard v2.0 using the pH 4-7 calibration sequence? The product's been out for a couple years at least, so it's hard to believe this could be a generic fault to these devices without somebody noticing.

I've sent a note to DA's support email address. I'll follow-up to describe how this plays out.

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n2585722
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby n2585722 » Sat Sep 20, 2014 4:48 pm

I think you have to change the 10 to read 4 when calibrating. They are setup for saltwater which is 7 and 10. I have not tried to calibrate one with 4 and 7 just 7 and 10.
thanks,
Danny

Edward
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sun Sep 21, 2014 6:34 am

Danny,

Thanks for the reply. I'm hoping somebody can confirm they've actually managed to get a unit to calibrate using the pH 4 - pH 7 procedure.

On your "change the 10 to read 4 when calibrating," there's nothing in the documention, no switch on the device, no configuration option in the web interface. The only apparent differentiation is the two calibration buttons in the web interface. Left one is for pH 7-10. Right one is for pH 4-7. Clicking the right one provides a simple instruction:

Step 3 - Rinse and clean your probe
Rinse your pH probe in the cup of RODI water and make sure the tip is clean of objects.

Step 4 - Next, place the pH probe in the 4pH calibration solution. It is often beneficial to allow your probe to stabilize in the solution for a couple of minutes before calibration is started. When you are ready to proceed, hit the "Start" button below.

These are strightforward instructions, right? Rinse. Put the probe in a pH 4 buffer solution, give it a few minutes to settle, then click the "start" button. The problem is, when I do so, the device then calibrates to 7.00, using the pH 4.001 buffer solution. Second calibration step, in the pH 7.001 buffer solution, calibrates to 10.00. This produces a unit that reads pH 6.4 water as pH 9.4.

Edward

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n2585722
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby n2585722 » Sun Sep 21, 2014 7:21 am

I have one I will try an calibrate it to 4 and 7. I will have to round up everything an try.
thanks,
Danny

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n2585722
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby n2585722 » Sun Sep 21, 2014 10:17 am

OK, it tried calibrating using 4 and 7. After calibration the 7 solution was reading 10. After some trial and error it seems that even though it ask for pH 4 solution it is calibrating it at 7. When it ask for pH 7 solution it is calibrating to 10. So it tried a calibration when ask for 4 I used pH 7 solution. When it ask for 7 I used 10 solution. I did this twice and it is now reading 10 in the 10 solution, 7.02 in the 7 solution and 4.01 in the 4 solution. So the maximum error is .02 at pH 7. I may not. Have left it in the 7 solution long enough when rechecking. Until DA can look into this I would recommend calibrating at pH 7 and jpH 10 then check it in the pH 4 solution to see how close the reading is. I will report this issue to Eric.
thanks,
Danny

Edward
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sun Sep 21, 2014 11:43 am

Danny,

Thanks for going through the trouble of trying it out. You've confirmed the product generally has this fault.

Yes, I agree. The work-around is to only use the pH 7 .. pH 10 procedure. I've ordered enough packets of pH 10.001, to match what I've got left of the pH 7.001. (Anybody want to buy my extra 10x Milwaukee pH 4.001 buffer packets? Expiration dates are all 03/2019)....

Edward

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n2585722
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby n2585722 » Sun Sep 21, 2014 12:44 pm

You can use the pH 4 to confirm the calibration is OK for your use.
thanks,
Danny

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DaveMorris
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby DaveMorris » Sun Sep 21, 2014 2:22 pm

Just out of curiosity, why are you trying to calibrate it with 4 and 7 solutions? Is it a freshwater tank? If it is a saltwater tank, you should be calibrating it with 7 and 10. You want your calibration points on either side of your expected normal reading and as close to it as possible. I know a while back there was a known issue with calibrating probes below 6.0, but I thought it had been fixed. Maybe that fix was missed in the LifeGuard.
Dave
My tank: http://www.sdreefs.com/forums/showthread.php?103096-My-300g-to-120g-Upgrade
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Edward
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Re: pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sun Sep 21, 2014 6:38 pm

DaveMorris,

Yes, it's a planted freshwater tank. Typical range on any given 24 hour day is about pH 6.6 to 7.0. And, yes, I understand a calibration typically produces a linear formula straddling the intended range of use. It's the basis for estimating the intermediate points. So accuracy is best near either of the two samples. And, since the actual behavior of a probe is ordinarily better modeled as a curve, not a line, having to resort to a pH 7 - 10 calibration will produce a somewhat less accurate meter for my situation.

Edward

Edward
Posts: 8
Joined: Sat Sep 13, 2014 6:58 am
How many years have you been in the hobby?: 45

Re: pH calibration 4.00 - 7.00 is FUBAR

Postby Edward » Sun Sep 21, 2014 6:52 pm

n2585722,

Yes, after I get it calibrated via the pH 7 - 10 procedure, I can check how closely it reads a pH 4.001 sample. However, since I only have pH 4.001 and 7.001 solutions at the moment, I can't complete the pH 7 - 10 calibration. The procedure fails after the first sample, which leave the meter completely dysfunctional. It thinks everything is ~pH 7.00. So until I receive the pH 10.001 buffer solution packets, the meter is useless.

Edward


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