Calibrating electronic Ph meter

Netlist · 13th April 2007, 04:14 PM

Is there a way to calibrate an electronic Ph meter?
A liquid with a known stable Ph value would do the trick, only what should I look for?

/Hugo

SY · 13th April 2007, 04:38 PM

You want two buffer solutions at pH values which are 3 or 4 apart (for example, pH = 5 and pH = 8). Any chemical supply place will have them.

Netlist · 13th April 2007, 04:51 PM

Thanks, I know a few in town.
As for the trimming, there's only one pot so both liquids will only be able to make me adjust indicatively.

/Hugo

RDL2004 · 13th April 2007, 08:12 PM

You need what is called "buffer solutions". They are made specifically for calibrating pH meters.

They come in many pH values. For better meters with 2 point calibration you usually use something like 4 and 10.

For meters with only 1 point calibration (which it seems yours is) it is usually best to pick a buffer value near the pH which you will be measuring.

Also, temperature will affect the pH reading, more expensive meters will have built in temperature compensation.

I think the buffers must be at a certain temperature to be the specified pH, probably 25C.

Juergen Knoop · 13th April 2007, 08:21 PM

afaik, one point trimming is better done with a pH 7 buffer
because the probe change their asymmetry far more, than their slope
I have had several used probes, even really cheap ones, with nearly perfect 57-59mV/pH at room temperature, but asymmetry up to hundreds of mV in one case

I think you can also use pH 4 or 6,81 buffers, this shouldn't matter with a simple pH-stick
just don't use dest. water as some people recommend
it has not pH 7 and the probe will give no reliable readings with such unbuffered water
regards

SY · 13th April 2007, 08:50 PM

That's exactly it- "buffer" is the key word. Because pH is logarithmic, a deviation of 1 pH unit on either side of neutral (ph= 7) is a very, very tiny change in hydronium/hydroxyl ion concentration. Purified water will NOT work. As with amplifiers driving a load, a buffer is called for.

XEAGLEKEEPER · 13th April 2007, 11:27 PM

A company called Hach sells the buffer solutions
http://www.hach.com/

Dave

Netlist · 14th April 2007, 06:46 AM

Thanks a lot everyone.
That's a wealth of useful information.

/Hugo

13th April 2007, 04:38 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	You want two buffer solutions at pH values which are 3 or 4 apart (for example, pH = 5 and pH = 8). Any chemical supply place will have them. __________________ If there's a sucker born every minute, where do the rest of them come from?

13th April 2007, 08:50 PM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	That's exactly it- "buffer" is the key word. Because pH is logarithmic, a deviation of 1 pH unit on either side of neutral (ph= 7) is a very, very tiny change in hydronium/hydroxyl ion concentration. Purified water will NOT work. As with amplifiers driving a load, a buffer is called for. __________________ If there's a sucker born every minute, where do the rest of them come from?

13th April 2007, 11:27 PM	#7
XEAGLEKEEPER diyAudio Member Join Date: Jan 2006 Location: central Iowa	A company called Hach sells the buffer solutions http://www.hach.com/ Dave __________________ Ret. USAF... AKA- Avionic * Solder slinger for hire...*

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13th April 2007, 04:51 PM	#3
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	Thanks, I know a few in town. As for the trimming, there's only one pot so both liquids will only be able to make me adjust indicatively. /Hugo

13th April 2007, 08:12 PM	#4
RDL2004 diyAudio Member Join Date: Oct 2004	You need what is called "buffer solutions". They are made specifically for calibrating pH meters. They come in many pH values. For better meters with 2 point calibration you usually use something like 4 and 10. For meters with only 1 point calibration (which it seems yours is) it is usually best to pick a buffer value near the pH which you will be measuring. Also, temperature will affect the pH reading, more expensive meters will have built in temperature compensation. I think the buffers must be at a certain temperature to be the specified pH, probably 25C.

13th April 2007, 08:21 PM	#5
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	afaik, one point trimming is better done with a pH 7 buffer because the probe change their asymmetry far more, than their slope I have had several used probes, even really cheap ones, with nearly perfect 57-59mV/pH at room temperature, but asymmetry up to hundreds of mV in one case I think you can also use pH 4 or 6,81 buffers, this shouldn't matter with a simple pH-stick just don't use dest. water as some people recommend it has not pH 7 and the probe will give no reliable readings with such unbuffered water regards

14th April 2007, 06:46 AM	#8
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	Thanks a lot everyone. That's a wealth of useful information. /Hugo

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