Control Engineering and Automation Technology
Core concepts
Understand open-loop versus closed-loop control, the control loop elements (setpoint, controller, actuator, plant, sensor, disturbance), and standard controller types: P, I, D, PI, PID. Know how proportional gain affects speed of response and steady-state error, how integral action removes offset, and how derivative action damps overshoot. Be familiar with step response characteristics: rise time, overshoot, settling time, steady-state error. In automation, cover PLC programming (ladder, function block, structured text), sensors, actuators, fieldbus systems and safety functions.
Traps in questions
- Saying P-control removes steady-state error (it does not; I-action does).
- Increasing gain to fix everything; high gain causes oscillation.
- Confusing a disturbance with a setpoint change.
- Ignoring scan time and sensor delay in PLC logic.
- Mixing up normally open and normally closed contacts in ladder logic.
Worked example
A temperature loop with pure P-control has gain K = 4 and a process with steady-state gain 0.5. For a setpoint of 100 °C, the steady-state error is e = setpoint/(1 + K·process gain) = 100/(1 + 2) ≈ 33 °C. Adding integral action drives this error to zero over time. Rule of thumb: tune P first for stable response, then add I to remove offset, then D only if overshoot remains.
Practical competence
Be able to read a control loop diagram, identify the controlled variable and disturbance, and describe how a PLC program executes cyclically. Understand safety-related control (emergency stop, safety relays) as distinct from standard control.