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Old 12-22-2011, 09:08 PM   #31
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Quote:
Originally Posted by ryclo View Post
Hanna Temp/PH pen for $69.95 with free shipping is hard to beat!

Hanna HI 98127 pH Tester - Mitchell Instrument Company
Is there any advantage to ordering with the 'NIST' calibration certificate for $13 more?
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Old 12-22-2011, 10:06 PM   #32
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I'm not sure what NIST calibration would do for you with a pH meter. That might be valid for a short while. But as the probe ages, the calibration goes out the door. You really have to perform calibration checks on a daily basis to make sure that the meter electronics haven't shifted and the probe chemistry and function is still correct.
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Old 12-22-2011, 11:11 PM   #33
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Quote:
Originally Posted by kincade View Post
Is there any advantage to ordering with the 'NIST' calibration certificate for $13 more?
What does 'NIST' stand for? Nice Idea for Skinning the Turkeys? I'd stay away from this outfit. I have never seen NIST calibration offered for a pH meter and to even suggest such a thing for a device with 0.1 pH specified accuracy seems a cruel joke. And I can't imagine what it would even mean. A pH meter is basically a sensitive volt meter but one doesn't need to have an absolute voltage calibration on the thing because the user must calibrate it himself before every use. It is recommended that he use NIST traceable buffers and so I can only imagine that it means they do a calibration using NIST buffers before shipping which would be worthless because you would have to recalibrate it yourself the first time you used it.

 
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Old 10-03-2012, 09:19 PM   #34
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NIST stands for National Institute of Standards and Technology. Its third party proof that the tester is meeting the accuracy claims by the manufacturer. If you are an ISO9000 facility you are required to have this on any equipment you use, if you dont know what it is you do not need it as it does not do anything to the accuracy of the instrument.

 
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Old 10-03-2012, 11:01 PM   #35
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That's not true. I don't know what the NIST calibration standard calls for but I would assume that a check on the accuracy/linearity of the RTD and a check on the linearity of the A/D are involved (offset isn't so important here because that would get calibrated out). Both of those effect the accuracy of pH meter readings. But on an 'instrument' with an 0.1 pH accuracy spec?

[Edit] Another thing I'd really like to see verified is the isoelectric pH of electrodes. I wonder if they do that in NIST certification (of real meters which costs about $150 - not the ridiculous $19 'NIST certification' for the $69 meter). The reason I'm hard over on it is that I once bought an expensive electrode that had an isoelectric pH way out of spec. The electrode is perfectly useable (I've had it for years) but I have to do cal/pH/ATC in my own software which works with arbitrary pHi.

 
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Old 10-04-2012, 12:53 AM   #36
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How do you feel about an $83 NIST cert on a $75 meter?

http://www.mitchellinstrument.com/ha...ph-tester.html
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Old 10-04-2012, 02:19 PM   #37
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If you are worried about accuracy, you would not buy a $75 ph meter in the first place. NIST traceability is simply comparing the readings of the ph meter to a calibration standard (this standard is traceable all the way back to the gov't NIST labs) and verifying that the instrument is as accurate as the specs say its supposed to be. There is no standard accuracy that the NIST labs say all PH testers must meet. A NIST cert is not a calibration of the device.

 
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Old 10-04-2012, 02:33 PM   #38
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Yoop, did you end up getting that Milwaukee 56? How do you like it? Seem to work well for you?
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Old 10-04-2012, 02:40 PM   #39
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Yoop, did you end up getting that Milwaukee 56? How do you like it? Seem to work well for you?
Well, I like it, in that it's easy to use. But I have had some troubles with it. They've replaced the electrode twice, and I sent it in once to them. They haven't charged me, but it came back last week and I used it. I calibrated it, and within a couple of minutes it was drifting again, pretty badly. I calibrated it again, and it seemed ok then. If I had it to do over, I would have chosen a different meter.
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Old 10-04-2012, 02:43 PM   #40
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I was thinking about buying one, but I'm not sure how much of an improvement it would be over the ColorpHast pH strips I have now. I know Kai's done some work showing that the strips aren't all that accurate, but I'm not sure if any of the meters in this price range are much better.
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