Control Talk Blog

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.

Steps to Better Process Control Tips (Part 2)

We continue this series with the steps for designing control strategies. Simple rules of thumb will be offered for setting up cascade, composition, flow, level, pH, pressure, and temperature control systems. Examples of common unit operations will help provide understanding of the steps involved.  The objective is to set the...

Steps to Better Process Control Tips (Part 1)

We start this series with the steps for the selection and installation of the field measurements and control valves or variable speed drives to enable the control system to meet plant objectives. The measurement is the essential window into the process and manipulating a flow is the essential way to...

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

We conclude this series with a look at how to tune a controller when the objective is to maximize the absorption of variability rather than tight control of the process variable. The details for the most common case of surge tank level control are provided.

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.

Checklist for PID Migration Tips

Older Distributed Control Systems (DCS) and analog controllers tended to have different tuning setting units and methods of implementing integral and derivative action. A lack of understanding of the difference between the old and new PID features and tuning settings can lead to poor and even unstable control when migrating...

When do I Use MPC instead of PID for Advanced Regulatory Control - Tips?

For advanced regulatory control, when do I use Model Predictive Control (MPC) instead of PID control? There are many PID techniques for dealing with batch operations, abnormal operation, startups, and transitions. Feedforward, ratio control, and override control are a main stay for PID control.  If desired, PID dead time compensators...

When do I Use PID, MPC, and FLC for Basic Control - Tips?

For basic control, when do I use Fuzzy Logic Control (FLC) and Model Predictive Control (MPC) instead of PID control? The automation and integration of FLC and MPC into distributed control systems makes these a more viable choice. Surprisingly, there may be less decisions and expertise required than for PID control.