Roadmap › Industrial Automation — PLC, SCADA, Modbus and OPC UA › Module: PLC Programming
Lessons in this course (10)
5. PID control loops
IntermediateMediumLesson 5 of 10
Closed-loop control: measure the process variable (PV), compare with the setpoint (SP), and adjust the output (CV/MV) to reduce the error.
text
SP ──►(+)──error──► PID ──CV──► valve/heater ──► process ──► PV
▲(−) │
└──────────────────── sensor ◄───────────────────────┘| Term | Effect |
|---|---|
| P — proportional | Output proportional to current error; too high → oscillation; alone leaves steady-state offset |
| I — integral | Accumulates past error; removes offset; too much → overshoot, windup |
| D — derivative | Reacts to rate of change; damps overshoot; sensitive to noise |
Practicalities: anti-windup, bumpless transfer between manual and auto, output limits, filtering noisy signals, tuning methods (Ziegler–Nichols, step-response, auto-tune in the PLC). Examples: temperature of an oven, tank level, pressure, motor speed.