The method for automatic tuning automatically determines the value of the parameters listed in table 4-1 in the image above. The 2208e and 2204e uses a “one-shot” tuner in which works by switching the output on and off to induce an oscillation in the measured value. From the amplitude and period of the oscillation, it calculates the tuning parameter values.

If the tuning process cannot tolerate full heating or cooling being applied, then the level of heating or cooling can be restricted by setting the heating and cooling power limits in the Output list. However, the measured value must oscillate to some degree for the tuner to be able to calculate values.

A one-shot Tune can be performed at any time but normally, it is performed only once during the initial commissioning of the process. However, if the process under control subsequently becomes unstable (because its characteristics have changed), you can re-tune again for the new conditions.

It is best to start tuning with the process at ambient temperature. This allows the tuner to calculate more accurately the low cutback and high cutback values that restrict the amount of overshoot or undershoot.