I'm looking to get a pH meter. I understand everyone has their preference and am looking for objective opinions on sub $30-$40 pen style meters.
I'm not looking for the supreme accuracy and precision of the more expensive units but would like something that can confirm my Bru'n water predictions with better accuracy than strips.
Any suggestions would be welcome.
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The best $41.00 pH meter is the HI98100 Hanna Checker pH meter.
http://hannainst.com/hi98100-checkerr-plus-ph-tester.html
Has: auto-two point calibration, replaceable pH electrode, stability indicator and low battery level indicator.
Does not have: ATC, temperature readout
The probe supplied is an open junction design. Make sure you place storage solution in the cap when not in use. An open junction is susceptible to drying out since it is a hard gel layer. Do not use above 50 oC since the gel (agar like) will melt. The open junction should provide a good response time in water. Just calibrate at the saem temperature the water is. The packets of buffer have a chart that will tell you the solution pH at a particular temperature (not ATC). This is the value to use for calibration.
The Checker is supplied with carrying case, pH 4 and 7 sachet, and cleaning solution sachet.
The Cadillac of testers is the pHep 5 HI98128. That is approaching $100.00. The HI98128 is the same electronics found in some portables. The main difference will be the probe. A small cartridge style and compared to traditional field probe (12mm x 160mm) with BNC connector.
The best portable on the planet is the HI98191but at $565 it is out of the reach of most hobbyist. Too many features to list but basically a professional portable meter.
But for $41 dollars the HI98100 Checker pH meter is good meter.
The trick to long life is in the maintenance. Rinse between measurements, periodically cleaning and using a storage solution.
This was the meter that made me post. As discussed in this thread though, the accuracy is poor.
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It would be surprising to see if anyone actually achieves the accuracy as stated by a meter. The accuracy statement is the the mV accuracy of the meter itself and not the complete system. To obtain a high level of accuracy +/- 0.05 pH the following would be needed:
1) pH probe with an offset +/- 15 mV and slope >95%
2) Calibrated in fresh buffers
3) pH probe is properly hydrated
4) Use of a magnetic stirrer for mixing
5) Proper temperature equilibration time for the pH and reference cells to match sample temp.
Since most people do not monitor offset and slope or use best practices it is very likely that a high level of accuracy is realized. We recently did a study on measuring pH of cheese, dough and meat with at least 3different probes for each sample (direct and slurry readings). Overall with new probes there was variation of up to 0.2 pH units. It was found that has more DI water was added to a sample (1 part product to 2, 10 parts water) that the readings drifted away from a direct measurement. It could be due to a decrease in conductivity of the sample (i.e. next time use 0.1M KCl for water to mix with). Either way there was some variation. I have seen this many times in which two probes read the same in a buffer but differ slightly in actual sample.
As far as three point calibration I would not use that as a determining factor when deciding on a pH meter. Most meters use a segmented slope in which the readings are based on the buffers that bracket it. For example, i calibrate to pH 4 , 7 and 10 and measure pH 5.2. The slope that he meter uses to calculate the reading is pH 7 and 4. The slope from pH 7 to 10 is not used. A meter can display an average slope which would be the average of the two but the meter should use the actual slope of two points since error would be introduced by the average slope. Basically slope A (7 & 4) for a pH electrode can be different than slope B (7 & 10).
For users of the pHep 5 place a small piece of sponge (portion of Scotch Brite pad)in the well and wet with solution. This will maintain the hydrated layer. Another advantage of the pHep 5 is that it does have a extractable junction. If the readings are drifting then pull out 1/8" of the junction to expose new surface. The flow rate from the junction will be like new providing for fast response time.
Topic: pH Meter: Balancing cost and quality (Read 8503 times)
