Control Talk Blog

Cascade Control Recommendation Tips

Given that cascade control loops are everywhere without much consideration as to dynamic requirements, what can we do to make the implementation effective? Here are some specifics by the way of detailed recommendations on the sequence, speed, and setup for tuning PID and digital valve controllers.

Cascade Control Perspective Tips

Did you know all loops today use cascade control? Do you understand how cascade control can correct for lower loop disturbances before they affect the upper loop and can make the upper loop faster? Do you know what to do to keep the system from oscillating if the lower loop...

Interactions Recommendations Tips

How do you know when interaction is going to be a problem? Why would the control loop design need to be changed? Are there hidden loops? What can you do with tuning to mitigate the problem? When do you need to move on to Model Predictive Control? Hopefully, this blog...

Effect of Interactions Perspective Tips

Since most unit operations have multiple loops and streams, interactions can exist where the PID output of one loop affects the PID process variable of another loop and vice versa. Interactions can cause loops to confusingly burst into oscillations.

pH and Temperature Measurement and Control Tips

Here is an opportunity to learn how to improve pH and temperature control systems and support ISA as well. Registrants for these web seminars receive a free copy of the respective book and free follow-up answers to questions that can be shared with ISA Mentor Program participants.

Extending Process Control Benefits Analysis Tips

What can be done besides the typical analysis for control benefits that show a setpoint can be moved closer to a constraint by reducing variability? Here we take a quick look at five things that can be done to extend this analysis to unknown effects and recognize and seek benefits...

Nonlinearities Recommendations Tips

We conclude our review of nonlinearities with an overview of applications and a detailed list of simple solutions to minimize the adverse effects of this everyday problem in nearly all control loops. It is impressive how setting lambda equal to 3x the largest deadtime value helps to solve most nonlinearity problems. Lambda...

Effect of Nonlinearities Perspective Tips

Here we use the broader definition of linearity to mean constant dynamics. A linear control loop has a constant total loop dead time, constant primary and secondary time constants, and a constant open loop gain. This perspective reviews the sources of dynamics and causes of nonlinearity.

Plant Speedup Stability Tips

The speedup of a plant’s response can cause loops to go from a smooth to an oscillatory response. In actual plants, the faster rate of change of a process variable important for product quality such a temperature or composition occurs for various changes in operating conditions.

The Primary Source of Disagreement in Process Control Tips

The primary reason why there are so many and so different schools of thought about control algorithms and tuning can be traced back to one parameter in the process response. What PID tuning and what PID structure is pronounced as best and even whether PID control should be used is...