Editing PH meter (section)

===Calibration and operation===
[[File:PH Meter 01.jpg|thumb|5.739 pH/Ion at 23 °C temperature shown on photo. pH 7110 pH meter manufactured by inoLab]]
The [[German Institute for Standardization]] publishes a standard for pH measurement using pH meters, DIN 19263.<ref name="DIN">{{cite web|title=pH Measurement - pH Measuring Chains|url=https://www.beuth.de/de/norm/din-19263/96105863|website=Beuth publishing DIN|publisher=Beuth Verlag GmbH|access-date=28 March 2017}}</ref>

Very precise measurements necessitate that the pH meter is calibrated before each measurement. More typically calibration is performed once per day of operation. Calibration is needed because the glass electrode does not give reproducible [[electrostatic potential]]s over longer periods of time.<ref name="Galster" />{{rp|238–239}}

Consistent with principles of [[good laboratory practice]], calibration is performed with at least two standard [[buffer solution]]s that span the range of pH values to be measured. For general purposes, buffers at pH 4.00 and pH 10.00 are suitable. The pH meter has one calibration control to set the meter reading equal to the value of the first standard buffer and a second control to adjust the meter reading to the value of the second buffer. A third control allows the temperature to be set. Standard buffer sachets, available from a variety of suppliers, usually document the [[temperature dependence]] of the buffer control. More precise measurements sometimes require calibration at three different pH values. Some pH meters provide built-in temperature-coefficient correction, with temperature [[thermocouples]] in the electrode probes. The calibration process correlates the voltage produced by the probe (approximately 0.06&nbsp;volts per pH unit) with the pH scale. Good laboratory practice dictates that, after each measurement, the probes are rinsed with [[distilled water]] or [[deionized water]] to remove any traces of the solution being measured, blotted with a scientific wipe to absorb any remaining water, which could dilute the sample and thus alter the reading, and then immersed in a storage solution suitable for the particular probe type.<ref name="all-about-pH">{{cite web|title=How to perform a pH meter calibration|url=http://www.all-about-ph.com/ph-meter-calibration.html|website=all-about-pH.com|access-date=14 December 2016}}</ref>