Ph meter question from a newb

[beerisyummy]

I appreciate in advance any comments by those more knowledgeable than myself!

I'm no scientist. My Dad was a physicist, but I became a musician. So when I try to read formulae, they just blur in fronta me eyes. But, I have a general grasp of processes and "big picture stuff."

So I bought a ph meter. It's a Dr. Meter PH-100, which has 0.01 accuracy and temp compensation; and since I only brew once a month, I didn't see any reason to spend over $100. Hopefully I will not regret the decision.

I bought the standard 4, 7, and 10 calibration solutions. Then I open up the instructions, and it says to calibrate to 6.86, 4.00 and 9.18.

wtf .... is this an issue or a non-issue?

 

[ajdelange]

There are plenty of reasons to spend ca. $100 the main one being that you get a meter which works for more than 6 months.

You have bought a meter that calibrates to NIST buffers rather than the standard NIST traceable operational buffers. To use this meter you will have to buy a set of the NIST buffers or rather the 6.86 one as the 4 buffer is, AFAIK, the same and you do not need the 10 buffer in brewing. Your best bet would be to write off the $50 you paid for this meter as a learning experience and get one that used the standard buffers. There are hundreds of posts here that talk about which ones these are.

There are workarounds. You can probably calibrate this meter with standard pH 7 buffer and correct the readings but they will be a little shaky and you will probably have to dispense with ATC. If you don't like formulas you aren't going to like the correction procedure.

I note that no one sells this meter any more. Probably because of the buffer issue.

 

[beerisyummy]

There are plenty of reasons to spend ca. $100 the main one being that you get a meter which works for more than 6 months.

You have bought a meter that calibrates to NIST buffers rather than the standard NIST traceable operational buffers. To use this meter you will have to buy a set of the NIST buffers or rather the 6.86 one as the 4 buffer is, AFAIK, the same and you do not need the 10 buffer in brewing. Your best bet would be to write off the $50 you paid for this meter as a learning experience and get one that used the standard buffers. There are hundreds of posts here that talk about which ones these are.

There are workarounds. You can probably calibrate this meter with standard pH 7 buffer and correct the readings but they will be a little shaky and you will probably have to dispense with ATC. If you don't like formulas you aren't going to like the correction procedure.

I note that no one sells this meter any more. Probably because of the buffer issue.

AAARRRGGHHH. Thank you for the info.
Did I mention AAARRRGHHH

 

[ajdelange]

I thought about it a bit more and perhaps the situation isn't so dire. The 6.865 buffer is available (https://www.labsource.com/51350054-nist-ph-buffer-6-865-250ml). With that you will be able to calibrate and use your meter as it was intended to be used. The catch is that the buffer is about half the cost of the meter and you have already invested in the NIST traceable buffer. The less expensive meters tend to fail sooner than the more expensive ones but this is a probalistic thing and the particular one you have in hand may last appreciably longer than average (or not nearly as long). When it dies think about replacing it with one of the meters recommended here.

Were I in your position I think I would try to calibrate the meter with the buffer you have. It will think the slope is 102.4% which it should allow. Do the calibration at room temperature and cool all sample to room temperature before reading. The important thing is that buffer and sample temperatures are the same.This effectively turns ATC off and I don't think you want to rely on ATC using this scheme. Five degrees or so difference should be OK. Subtract 4 from the meter's reading for each sample and multiply the result by 0.471. Add that to the meter reading. Example: You check the 4 buffer. The meter should read 4. Subtract 4 from that to get 0. No correction as the meter was calibrated using 4 buffer. Now check the 7 buffer. The meter will read 6.865 (or would if it were perfect and displayed 3 decimal places). Subtract 4 to get 2.865. The correction is then 0.0471*2.865 = 0.134942. Adding that to the reading of 6.865 gives 6.865 + 0.134942 = 6.99994 which, as this is actually 7.00 buffer, is the right answer. No formulas.

 

[beerisyummy]

I am all about simplicity. I'm returning the funky ph meter to Amazon, keeping the buffer solutions and just gonna trot over to my lhbs and get the Milwaukee with ATC for $135. Should be the last ph meter I'll ever need

I do appreciate your thoughts!