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...

Disturbance Dynamics Recomendations Tips

If there were no unmeasured disturbances, feedback control would not be necessary. Process engineers and operators could home in on the best PID output and just leave it at this value. In fact many process engineers are much more comfortable with setting a stream flow per a process flow diagram...

Effect of Disturbance Dynamics Perspective Tips

Much of the differences in approaches to controller algorithms and tuning can be traced back to assumptions made about the type and importance of disturbances. Each method has merits based on the disturbance frequency, location, and time lag.

The Root Causes of Slow Oscillations Tips

Slow oscillations can be difficult to recognize especially when the period is beyond the typical time frame of the trend chart or there are intervening disturbances or recycle. Slow oscillations can be more detrimental to product quality because the large period means the amplitude is less attenuated by intervening volumes.

A Unified Approach to PID Control Steps 1-5 Tips

A unified approach to PID Control has been found that enables a common and simplified method for setting PID tuning parameters. Key features can be used to eliminate the need for retuning to deal with different dynamics and objectives.

How to Avoid a Common PID Tuning Mistake Tips

The process variable has slow decaying oscillations. Control theory text books indicate decreasing the PID gain should make the loop more stable. You decrease the PID gain. The oscillation gets worse. You decrease the gain again. The amplitude and the period get bigger. You repeatedly decrease the PID gain.

Processes with no Steady State in PID Time Frame Tips (Part 2)

We are aware that too high of a PID gain can cause excessive oscillations and even instability. The ultimate gain for processes with no steady state on PID horizon is usually much higher than our comfort level.

Processes with no Steady State in PID Time Frame Tips (Part 1)

Many of the most important process variables, such as vessel and column composition, pressure and temperature, do not reach a steady state in the time frame of PID action. Batch composition, pH and temperature and, of course, level have no steady state.

Basics of PID Control Modes Tips

The PID is by far the most prevalent controller in the process industry. Here we step back for a view of the basics of the proportional, integral, and derivative modes. These PID controller modes have distinct advantages and disadvantages and consequences if one mode dominates.