- •Distributed Control Systems (DCS)
- •Fieldbus control
- •Practical PID controller features
- •Manual and automatic modes
- •Output and setpoint tracking
- •Alarm capabilities
- •Output and setpoint limiting
- •Security
- •Digital PID algorithms
- •Introduction to pseudocode
- •Position versus velocity algorithms
- •Note to students
- •Proportional plus integral control action
- •Proportional plus derivative control action
- •Full PID control action
- •Review of fundamental principles
- •Process dynamics and PID controller tuning
- •Process characteristics
- •Integrating processes
- •Runaway processes
- •Lag time
- •Multiple lags (orders)
- •Dead time
- •Hysteresis
- •Before you tune . . .
- •Identifying operational needs
- •Identifying process and system hazards
- •Identifying the problem(s)
- •Final precautions
- •Quantitative PID tuning procedures
- •Heuristic PID tuning procedures
- •Features of P, I, and D actions
- •Tuning recommendations based on process dynamics
- •Tuning techniques compared
- •Tuning a liquid level process
- •Tuning a temperature process
- •Note to students
- •Electrically simulating a process
- •Simulating a process by computer
- •Review of fundamental principles
- •Basic process control strategies
- •Supervisory control
- •Cascade control
- •Ratio control
- •Relation control
- •Feedforward control
- •Load Compensation
- •Proportioning feedforward action
- •Feedforward with dynamic compensation
- •Dead time compensation
- •Lag time compensation
- •Lead/Lag and dead time function blocks
- •Limit, Selector, and Override controls
- •Limit controls
Chapter 30
Process dynamics and PID controller tuning
To tune a feedback control system means to adjust parameters in the controller to achieve robust control over the process. “Robust” in this context is usually defined as stability of the process variable despite changes in load, fast response to changes in setpoint, minimal oscillation following either type of change, and minimal o set (error between setpoint and process variable) over time.
“Robust control” is far easier to define than it is to achieve. With PID (Proportional-Integral- Derivative) control being the most common feedback control algorithm used in industry, it is important for all instrumentation practitioners to understand how to tune these controllers e ectively and with a minimum investment of time.
Di erent types of processes, having di erent dynamic (time-dependent) behaviors, require di erent levels of proportional, integral, and derivative control action to achieve stability and robust response. It is therefore imperative for anyone seeking to tune a PID controller to understand the dynamic nature of the process being controlled. For this reason, the chapter begins with an exploration of common process characteristics before introducing techniques useful in choosing practical P, I, and D tuning parameter values.
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