What is a PID?
A PID controller (Proportional-Integral-Derivative) is a control algorithm used to keep a process variable, such as temperature, pressure or flow rate, constant at a desired value (the Setpoint). PID controllers are widely used in PLCs, DCS systems and field instrumentation in industry.
PID is the standard for accurate and stable process control.
🎯 What does a PID control?
A PID continuously compares the measured value (PV - Process Value) with the desired value (SP - Setpoint) and, based on this, drives an output signal (MV - Manipulated Variable) to an actuator such as a valve, motor or pump.
🔍 What do the PID components mean?
| Element | Full name | Effect on control |
|---|---|---|
| P | Proportional | Reacts to the difference between measured value and setpoint (the error) |
| I | Integral | Corrects slow, persistent errors (adds memory) |
| D | Derivative | Anticipates changes in the error (prevents overshoot) |
In formula form:
Output(t) = Kp·e(t) + Ki∫e(t)dt + Kd·de(t)/dt
Where:
e(t)= error (SP - PV)Kp,Ki,Kd= tuning parameters
🏭 Examples of PID applications
| Application | Controls… | Actuator |
|---|---|---|
| Temperature control | Temperature in a tank or oven | Heater or cooling valve |
| Pressure control | Pressure in a pipe or vessel | Control valve or compressor |
| Flow control | Flow rate of liquid or gas | Control valve or variable-frequency drive |
| Level control | Liquid level in a tank | Pump or drain valve |
| Speed control | Motor speed on a conveyor belt | Variable-frequency drive (VFD) |
⚙️ PID in OT systems
| System | Role in PID |
|---|---|
| PLC | PID blocks in the program execute the control |
| DCS | Central tuning and monitoring of PID loops |
| SCADA | Visualisation of SP, PV, MV and tuning parameters |
| Historian | Logging of PID performance and trend analysis |
🔧 PID tuning: why it matters
A poorly tuned PID can cause:
- Overshoot (the value goes past the setpoint)
- Slow response or instability
- Oscillations (values swing around the setpoint)
Tuning is done either manually or automatically using methods such as Ziegler-Nichols or model-based tuning.
📌 In summary
A PID controller keeps process variables automatically at the desired value through smart correction of deviations. It is an essential part of virtually all industrial control processes — reliable, flexible and universally applicable.