Biggest Opportunities for Process Control Improvement – Controller Tuning – Part 2

Oscillations are indicative of a controller that is tuned too fast unless the oscillations are very slow or are limit cycles caused by valve stick-slip for any type of process or valve dead band for an integrating process (e.g. level). The amplitude of fast oscillations that are not limit cycles can be reduced by decreasing the controller gain. Oscillations in the process variable may upset other loops and show up as off spec product if there are insufficient blend volumes downstream. Oscillations in the controller output may cause similar problems by affecting other process variables. Also, such oscillations make it more difficult to see patterns in process behavior either visually or by data analytics. Loops with a dead time approaching or exceeding the process time are often tuned too fast.