🔍 Key Concepts
• PID controller basics – what each term (P, I, D) actually does to the control signal
• The difference between error, output, setpoint, and input in a control loop
• How a proportional relationship is normally defined in control theory
💭 Think About
• For each choice, ask: in a standard PID loop, what is this component mathematically based on – the error, the integral of error, or the derivative (rate of change) of error?
• Focus on what a derivative term responds to: is it changes in the output, or changes in the error signal?
• Think about the proportional term: when we say something is proportional, which two quantities are directly related in basic control action?
✅ Before You Answer
• Be clear that in most textbook PID definitions, all three terms act on the error (setpoint – measured value), not directly on the process output itself
• Verify which option correctly describes a linear/proportional relationship between two variables, without swapping which is input and which is output
• Check that the description of the integral term involves accumulation over time, not an instantaneous one-to-one proportionality