The output voltage of a pH electrode varies with temperature in a manner predicted by theory -- the Nernst Equation. When required, Automated Aquarium Systems can supply electrodes with built-in automatic temperature compensation. The need for automatic compensation depends on the temperature variation, the pH value being measured and the desired measurement accuracy.

As shown in the following table, the pH error due to temperature is a function of both the temperature and the pH value being measured. At a pH of about 7, there is no error due to temperature and, of course, at a temperature of 25 degrees C, there is no error. The more the temperature changes from the ambient calibration temperature and the more the pH departs from 7, the greater is the pH error. The teal colored temperature/pH combinations have zero error due to temperature effects and the plum colored combinations have less than 0.1 pH unit error.

Whether or not automatic temperature compensation is needed is determined by the application's accuracy requirement. For example, a waste water application with pH varying between 5 and 9 and temperature varying between 5 and 45 degrees C has a maximum error of 0.12 pH unit. If the needed acuracy is 0.5 pH unit, then automatic compensation is not needed. However, in a process liquid where pH varies from 3 to 11 and the temperature from 25 to 75 degrees C, the error is 0.6 pH unit and automatic compensation probably is required.

If you decide, after reviewing the table, that you want Automatic Temperature Compensation in your pH electrode system, see the Hanna Literature Page for information about Hanna Automatic Temperature Compensation probes for your pH system.