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pH and Conductivity (EC) Meters

What is pH Measurement?

pH is a measure of acidity or alkalinity. The amount of hydrogen ions (H+) causes a liquid to be acidic (high concentration of hydrogen ions) or alkaline (low concentration of hydrogen ions).  The pH range is measured from 0 to 14.  The pH scale is derived from the dissociation constant of water in the following equation:


                                                                H2O -> H+ + OH- = 1 x 10-14 (mol/L)2 = Kw
                                                                      (Kw is the dissociation constant of water).


A pH meter takes the input from the pH glass (high impedance mV) and the input from the reference sensor and compares these 2 values to get a resulting millivolt reading.  The reading in mV is converted to pH by the following guidleine:

                 Zero mV = pH 7

                 59.2mV per pH unit change

                 mV are + for pH <7 and mV are - for pH >7

What is Conductivity (Electrical Conductivity Meter or EC Meter) Measurement?

An electrical conductivity meter (EC meter) measures the electrical conductivity in a solution. Commonly used in hydroponics, aquaculture and freshwater systems to monitor the amount of nutrients, salts or impurities in the water. Electrical conductivity of water samples is used as an indicator of how salt-free, ion-free, or impurity-free the sample is; the purer the water, the lower the conductivity (the higher the resistivity). Conductivity measurements in water are often reported as specific conductance, which is the conductivity of the water at 25 °C.

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