Do not get caught up in accuracy of a pH meter. The accuracy statements are for the meter and not the probe and meter. It is very difficult to achieve better than 0.1 pH accuracy. It would require knowing how to use and an understanding of offest/slope.
The following are features in pH meters:
1) Replaceable electrode
. The pH electrode will last 1-2 years based on use. Being able to replace allows you to invest in a meter with nicer features knowing that you will only replace the probe in the future
- Waterproof meters tend to cost more but can be easily washed completely in fresh water.
3) Automatic Temp compensation
- If you are measuring mash at 140-150 oF then ATC will be necessary to correct for the change in the pH membrane potential
4) Automatic calibration
- Auto-calibration can be useful but be warned that with automatic calibration the meter will look for two criteria before accepting a calibration point. One is stability in that the readings are not stable then it will not lock on. The other is the voltage response of the electrode. If the voltage is outside a window +/-60-80 mV in pH 7 (Inside tip of pH probe is pH 7 solution, pH 7 on inside and outside = theoretically 0 mV) or slope is less than 85% then calibration will not be able to be performed. Not necessarily a bad thing since a bad offset and slope will lead to huge errors in readings. To be waterproof a meter will typically also have auto-calibration. Hard to have a meter that is waterproof with manual trimmers.
5) Automatic shut-off
: With auto shut off the meter will turn itself off automatically after a set time. Other meters have a switch. Leave the switch on and the batteries will drain.
6) Battery % level indicator:
Shows battery percentage remaining. Ensures not using batteries with low power that could impact the readings.
7) Temperature readout
: Useful to know temp of a solution. Most meters will use a thermistor based sensor that offers pretty high accuracy. Stability indicator
: Shows when a reading is stable. Good for those that have a 0.01 resolution meter and have a hard time deciding between 0.01 and 0.03 pH. It is nice to have but not that important.
Because I work for a mfg I am not going to reference models. The features above are common among mfg's in the market.
One thing to note is that the readings are only as good as the calibration solution and maintenance.
1) Depending on usage. sachets of buffers for 1 time use. Good for the person that might use 1x/month. Bottles are for the frequent user. A small jar can be used for daily calibration and refreshed periodically (weekly).
2) Rinse probe in DI (purified) water before placing storage solution (ideally storage. If no storage is available then use pH 4). Either place a small sponge in the cap and soak with solution or place solution in a glass that the meter is then placed in. It is important that the bulb/junction remains damp.
3) Temperature kills pH probes! At 25 o
C a probe will last 1-2 years. For every 25 o
C increase cut that in half. So at 50 o
C expect 6 month to 1 year. Be aware of pH probe limitations. Make sure that it is being used within operating specs (i.e. < 60 o
C). There are pH electrodes that have a different glass and design for high temperatures. If you come to depend on pH then a portable might be the investment in the future.