(a) Proportional Action:
Proportional action, also known as “P” action, is the fundamental component of a PID controller. It directly adjusts the controller output based on the error between the desired setpoint and the measured process variable. The output change is proportional to the error magnitude, with a higher error leading to a larger output change. This creates a corrective effect, driving the process variable closer to the setpoint.
(b) Integral Action:
Integral action, also known as “I” action, aims to eliminate steady-state errors. It continuously integrates the error over time and adds this accumulated value to the controller output. This means that even small, persistent errors contribute to the output, eventually forcing the process variable to reach the setpoint even if the proportional action alone is insufficient.
(c) Excessive Integral Action:
While beneficial for correcting steady-state errors, excessive integral action can have drawbacks:
- Overshoot: The integral term’s influence might grow too large, causing the controlled variable to rapidly overshoot the setpoint before settling down. This can lead to oscillations and instability in the system.
- Slow Response: Excessive integral action can slow down the system’s response to transient changes. The integrator focuses on accumulated errors, potentially neglecting sudden changes requiring quicker adjustments.
(d) Derivative Action:
Derivative action, also known as “D” action, anticipates future changes in the error based on its rate of change. It adds a component to the controller output proportional to the derivative of the error signal. This helps the controller react quickly to changing trends in the error, preventing large deviations from the setpoint.
(e) Excessive Derivative Action:
Excessive derivative action can also cause problems:
- Noise Sensitivity: The derivative term amplifies high-frequency noise in the error signal, leading to erratic controller output and control instability.
- Chattering: If the derivative action is too strong, it can cause the controller output to oscillate rapidly around the setpoint, even in the absence of significant errors. This phenomenon is known as “chattering”.