In physiology the Nernst equation is used for finding the electric potential of a cell membrane with respect to one ion.

Not all installations require automatic temperature compensation.  In fact, most of our industrial customers do not require ATC for stable pH control of their systems. 

Almost all controllers and transmitters today, have a manual temperature compensation setting.  This permits you to "dial in" the actual operating temperature pf the water you are monitoring.  The electronics in the controller will make the appropriate temperature compensation for the setting that you select, and correct for any error.

If you have a system where the temperature of the water changes significantly over time, you may want to consider using the auto temp comp capability of your controller.  Any Sensorex pH electrode can be matched with the appropriate ATC element.

When connected to your new (or existing) controller or transmitter, it will provide the auto temp comp that you need.  The temperature element is usually incorporated into the matching cable assembly (electrode holder).  When it is time to replace the pH electrode cartridge, the ATC element remains behind, sealed in the cable assembly, waiting for a fresh pH electrode. 

To determine if Automatic Temperature Compensation is required for your installation, see the table below.

The need for automatic compensation depends on three variables:

1.The changes in temperature

2.The pH value being measured

3.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.  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 GRAY colored temperature/pH combinations have zero error due to temperature effects and the light blue 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 accuracy is 0.5 pH unit, then automatic compensation is not needed.

In a process liquid where pH varies from 3 to 11 and the temperature varies 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 need Automatic Temperature Compensation in your pH electrode system, select the appropriate cable assembly (for submersion) or flow cell-cable (for in-line) or ATC Insertion assembly.

Note: Values in light blue are less than .1 error and may not require temperature compensation. 

Values in gray are temperature and pH in which there is no error in pH from temperature.