Playground · Feedback control

PID playground

A controller compares what you want (set-point) with what the sensor reads (process variable) and moves the actuator. Choose a process, move the three gains, and watch what each term does.

Process

A normalised process like most slow industrial loops. The set-point steps to 1 at t = 1 s; at t = 15 s a disturbance knocks the output down by 0.3.

Controller gains

Kp1.20

Ki0.50

Kd0.00

Try a preset

Real-world effects

Anti-windup

Stops the integral growing while the actuator is at its limit. Turn it off and push the actuator into saturation to see the overshoot it prevents.

Derivative on measurement

Differentiate the measurement instead of the error, so a set-point step gives no spike.

Measurement noiseoff

Real sensors are noisy. Watch what noise does to the D term.

Derivative filter τoff

Low-pass filter on the D term. Needed as soon as there is noise.

Extra dead timeoff

More transport or communication delay. Delay is what makes loops unstable.

Controller sample timeoff

A PLC or drive computes the PID every few milliseconds, not continuously. Slow sampling adds delay.

Actuator rate limitoff

A VFD ramps speed; a valve takes time to move. 0 means no limit.

The machine

Performance

Rise time (10–90 %): 2.44 s
Overshoot: 0.0 %
Settling time (±5 %): 3.81 s
Error before disturbance: 0.002
IAE: 1.994

Process variable and set-point

Set-point
Process variable

Controller output and the share of each term

Controller output
P term
I term
D term

Time30.0 s

Try this

Choose "P only". The output settles below the set-point. Now add a little Ki and watch the gap close.
Raise Kp slowly until the response starts to ring. Then add Extra dead time: the same Kp becomes unstable.
Turn on noise, then add Kd. The controller output becomes jumpy. Add a derivative filter to calm it.
On the tank or pump, turn anti-windup off and use large gains. Compare the overshoot with it on.