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 GREY coloured temperature/pH combinations have zero error due to temperature effects and the light blue coloured 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 you 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 grey are temperature and pH in which there is no error in pH from temperature.